Sleep and Exercise Recovery: What Is Known

Sleep and recovery from exercise (how sleep, naps, caffeine, supplements and trackers relate to training) · also called Sleep and recovery, sleep and exercise recovery, sleep for athletes, sleep and training, sleep extension, napping, sueño y recuperación, recuperación deportiva

Sleep and recovery research asks whether more or better sleep helps people recover from exercise and perform better. Too little sleep lowers performance in pooled studies, and sleep extension and napping were the most helpful strategies in small reviews, but the evidence is limited. Late caffeine reduces sleep. Sleep trackers estimate rather than measure sleep and no study read shows a tracker speeds recovery. Loud snoring with gasping or heavy daytime sleepiness needs a doctor.

General information, not medical advice. Last substantive update October 31, 2026 · Not medically reviewed. A named clinician has not signed off on this page. How this page is made

About Sleep and Exercise Recovery: What Is Known

Too little sleep lowers exercise performance in pooled studies, and sleep extension and napping were the most helpful strategies in small reviews, though evidence quality is limited. Late caffeine clearly reduces sleep. Tart cherry, magnesium, protein before bed and cold water have thin or mixed evidence. Sleep trackers estimate sleep, are weak on sleep stages, and no study read shows they speed recovery. Loud snoring with gasping, heavy daytime sleepiness or long-lasting tiredness needs a doctor.

What sleep and recovery from exercise means, and what this page covers

People often say sleep is the most important part of recovery from training. This page looks at what research shows in athletes and active people, and where it is still uncertain. It is information only, not a training or sleep plan. For everyday sleep habits see our Better Sleep and Sleep Hygiene pages; this page does not repeat them.

A 2020 expert consensus says elite athletes are prone to short, broken sleep, and that one number such as 7 to 9 hours for everyone is unlikely to be ideal. It recommends an individual approach based on the athlete's own sleep needs.

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Sleep loss, sleep extension and napping: what studies found

Going without enough sleep lowers performance. A 2022 review of 69 publications found an average fall of 7.56% in exercise performance after sleep loss, about 0.4% for every hour awake before the task, and a 2024 review of 27 studies in athletes found similar harm, largest after waking much earlier than usual. The effect of a smaller loss over one to three nights, the everyday case, is described as unclear.

Sleeping longer (sleep extension) and napping are the strategies with the most support, but the studies are small. A 2018 review of 10 studies (218 people aged 18 to 24) and a 2023 review of 25 studies found sleep extension and naps the most effective of the sleep strategies tested. A 2021 review could include only two studies and called its conclusion tentative. A 2023 review of 22 trials found naps of 30 to under 60 minutes improved performance and cut tiredness in young men, though trials varied a great deal.

In teenagers, studies link less sleep with more sports injuries: about 1.7 times the odds under 8 hours in one school study, and 1.58 times for chronic poor sleep in a review of seven studies. These are links, not proof.

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Sleep after exercise: evening workouts, cold water, cherry juice, magnesium and protein

A review of 23 studies found that a single evening workout did not harm sleep on average and slightly increased deep sleep, though very hard exercise ending within an hour of bedtime might make sleep worse. The NHS advises people with insomnia not to exercise for at least 4 hours before bed, so the right timing may differ by person.

Cold water immersion gave mixed results: no change in sleep in a trial of 11 cyclists, more deep sleep early in the night after whole-body immersion in 12 runners, and no effect in a 2023 review. Tart cherry juice was linked with longer sleep in two very small trials. Magnesium shortened time to fall asleep by about 17 minutes in older adults with insomnia, in weak trials. Protein before bed raised overnight muscle protein synthesis in a laboratory trial of 36 men, but nobody measured sleep or performance. These are hints, not proven recovery tools.

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Caffeine timing

Caffeine is the clearest sleep problem in this area. A 2023 review of 24 studies found caffeine cut total sleep time by about 45 minutes and sleep efficiency by 7%, and estimated that coffee should be drunk at least 8.8 hours before bed and a pre-workout serve at least 13.2 hours before to protect sleep time. A trial found 400 mg of caffeine disrupted sleep even when taken 6 hours before bed. People differ in how sensitive they are, so these are averages. The FDA cites 400 mg a day as an amount not generally linked with harm for most adults.

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Sleep trackers: the limits of judging recovery with a tracker

Consumer trackers estimate sleep; they do not measure it the way a hospital sleep study (polysomnography) does. In one lab study of seven devices, sensitivity for sleep was high (0.93 or more) but specificity for wake was low (0.18 to 0.54), and sleep stage scores were inconsistent. A 2025 meta-analysis of 24 studies found wrist-worn trackers differed significantly from polysomnography in sleep time, sleep efficiency and time awake, though they can still show general patterns. A 2023 study of 11 devices found stage agreement scores from 0.26 to 0.69.

Whether a tracker proves you have recovered is not established. No study read shows that wearing a tracker, by itself, speeds recovery. A sleep, readiness or recovery score is a company calculation, not a medical measure. Case reports describe orthosomnia, where worry caused by tracker data makes sleep worse; how often it happens is not known.

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Overtraining and when poor recovery needs a doctor

A joint consensus statement describes overtraining syndrome as long-lasting fatigue, falling performance and mood disturbance after too much training and too little recovery. It says other causes such as illness, not eating enough, iron or magnesium deficiency and allergies must be excluded first, and that no single marker meets all the criteria. Poor recovery that does not improve with rest is a reason to see a doctor.

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At a glance

Traditional uses history, not proof

Studied for research

Sleep loss and performance, a harm shown in two large reviews (moderate certainty)
Sleep and injury in teenage athletes, low certainty (observational)
Sleep extension, low certainty
Daytime napping, low certainty
Evening exercise and later sleep, low certainty
Tart cherry juice and magnesium for sleep, very low certainty
Protein before bed, insufficient evidence for sleep or performance
Cold water immersion and sleep, mixed
Late caffeine reducing sleep, moderate certainty
Sleep tracker accuracy compared with a sleep study, moderate certainty
Orthosomnia and overtraining signs, insufficient evidence

Main compounds

Caffeine
Tart cherry juice
Magnesium
Casein and whey protein

Common forms

Daytime naps
Extra time in bed (sleep extension)
Evening exercise
Cold water immersion
Wrist, ring and bedside sleep trackers
Pre-workout and caffeinated products

Research links: 2020 expert consensus: sleep and the athlete · 2022 review: effects of acute sleep loss on physical performance (69 publications) · 2023 review: do sleep interventions help athletic performance (25 studies) · 2023 review: daytime napping and sport performance (22 trials) · 2023 review: effect of caffeine on subsequent sleep (24 studies) · 2025 meta-analysis: wrist-worn sleep trackers compared with polysomnography · NHS: Sleep apnoea · Research Library · Genes & Biomarkers Library

What it is and its history

Accepted scientific name: Sleep and recovery from exercise (a research topic, not a single treatment)
Common names: Sleep and recovery (English); Sleep and exercise recovery (English); Sleep for athletes (English); Sueño y recuperación (Spanish); Recuperación deportiva y sueño (Spanish)
Family or group: Topic overview: how sleep affects performance, injury and recovery after exercise, and what people try (naps, extra sleep, supplements, cold baths, trackers) to improve it.
Look-alikes and adulterants: Name: Sleep hygiene; Note: Everyday habits that support sleep; has its own page in our Wellness section.; Name: Insomnia; Note: A sleep disorder that needs its own assessment; has its own page.; Name: Sleep apnea; Note: A breathing problem in sleep that can look like poor recovery; has its own page.; Name: Recovery scores; Note: Proprietary scores from watches and rings; explained on a separate page.

Traditional use and history history, not clinical proof

Tradition or era	Documented use	Source
Sports science guidance	A 2020 expert consensus on sleep and the athlete (Walsh and colleagues) reviewed sleep problems in elite athletes and produced a sleep toolbox for practitioners. It says a single target such as 7 to 9 hours for everyone is unlikely to be ideal and that napping and sleep extension need more research. No history older than modern sports-science guidance was read for this page.	p33144349

Traditional use shows how it was used. It does not show that it works or is safe today.

What is inside, and how it may work

What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.

Main compounds

Compound	Family	Where it is concentrated	Activity studied	Level of evidence
Caffeine	stimulant	Coffee 107 mg per 250 mL and a pre-workout serve of 217.5 mg in the review; 400 mg in a timing trial; the FDA cites 400 mg a day as a limit for most adults.	Reduces sleep time and efficiency when taken late in the day. ^{10 8 26}	Human data
Tart cherry (Montmorency) juice	fruit juice	Contains melatonin and plant chemicals, according to the trial abstract.	Studied for sleep in two small trials and for exercise soreness in a review. ^{13 16 12}	Human data
Magnesium	mineral supplement	Under 1 g, up to three times a day, in the reviewed trials.	Possible shorter time to fall asleep in older adults with insomnia. ¹⁷	Human data
Casein and whey protein	dietary protein	45 g before sleep in the trial.	Raised overnight muscle protein synthesis in a laboratory trial. ²⁴	Human data

Mechanisms, receptors and pathways

Target or pathway	What was found	Level
Perceived effort	In a trial of six nights of extended sleep, muscle activation did not differ, and the authors think the longer time to exhaustion was due to a lower sense of effort. ¹	Human (small trial)
Body temperature at bedtime	The review of evening exercise found that higher body temperature at bedtime went with poorer sleep efficiency, but that result disappeared when one study was removed. One cold-immersion trial measured lower core temperature after whole-body immersion. ^{23 4}	Human (small trials, fragile result)
Overnight muscle protein synthesis	Protein taken before sleep reached muscle and increased protein synthesis rates in a laboratory trial. This is a marker, not a performance result. ²⁴	Human (laboratory trial)
Tryptophan breakdown (IDO)	In the older-adult cherry juice pilot, cell experiments showed a compound in the juice blocked the enzyme IDO, which breaks down tryptophan. This was proposed as a possible route and was not shown to cause the sleep change. ¹⁶	Cell experiments (background) and human pilot

Isolated compounds versus whole extracts

Most studies tested single strategies (a nap, a night of extension, one juice, one drink) and results for one product or schedule cannot be assumed for another. Real recovery routines combine several things at once, and none of the trials read tested a full package against usual practice.

13benefits and uses looked at

30studies and sources checked

Moderate certaintybest evidence rating found

4lab markers tracked in trials

3 moderate certainty1 mixed findings4 low certainty2 very low certainty3 not enough evidence

What was looked at

The 13 benefits and uses checked for Sleep and Exercise Recovery: What Is Known, each with how strong the evidence is. Tap one to open it.

Sleep loss and athletic performanceModerate certainty
Sleep and sports injury in young athletesLow certainty
Sleep extension (sleeping longer) before or during trainingLow certainty
Daytime nappingLow certainty
Exercise in the evening and the sleep that followsLow certainty
Tart cherry juice and sleepVery low certainty
Magnesium supplements and sleepVery low certainty
Protein before bed for overnight muscle recoveryNot enough evidence
Cold water immersion after exercise and sleepMixed findings
Caffeine timing and the sleep that followsModerate certainty
How well sleep trackers measure sleep compared with a sleep studyModerate certainty
Orthosomnia: worry caused by tracking sleepNot enough evidence
Recognising overtraining and incomplete recoveryNot enough evidence

Lab markers tracked in the studies

Exercise performance testsSports or muscle-and-joint injuryTotal sleep time and sleep efficiencyTracker agreement with polysomnography

What is Sleep and Exercise Recovery: What Is Known good for?

The main things studied for sleep and recovery from exercise, and how strong the human evidence is for each. Many studies are small and in young men. Each result is for the exact study described, and none of it is a training or sleep plan.

Sleep loss and athletic performanceModerate certaintyTwo large reviews found that sleep loss lowers exercise performance, by about 7.6% on average in one, and most clearly after a whole night awake or after waking much earlier than usual. This is a harm of too little sleep, not a treatment. Sleep and sports injury in young athletesLow certaintyTeenage athletes who slept less were more likely to be injured in observational studies (about 1.7 times the odds under 8 hours in one school). It is a link, not proof that more sleep prevents injury. Sleep extension (sleeping longer) before or during trainingLow certaintySleeping longer for several nights was the most useful sleep strategy for later performance in small reviews, but only a handful of small studies exist. A trial in 12 men found a longer hold time, mainly because the effort felt lower. Daytime nappingLow certaintyA 2023 review of 22 trials found that a 30 to under 60 minute daytime nap improved thinking and physical tests and reduced tiredness in young men. Results varied a lot between trials. Exercise in the evening and the sleep that followsLow certaintyA review of 23 studies found a single evening workout did not harm sleep on average, but very hard exercise finishing within an hour of bed might. The NHS is more cautious for people with insomnia. Tart cherry juice and sleepVery low certaintyTwo tiny trials (20 healthy adults, 8 older adults with insomnia) linked tart cherry juice with longer sleep. No athlete sleep trial was read. Magnesium supplements and sleepVery low certaintyThree small trials in older adults with insomnia found a shorter time to fall asleep (about 17 minutes) with magnesium. None involved athletes and the evidence is weak. Protein before bed for overnight muscle recoveryNot enough evidenceProtein taken before sleep raised overnight muscle protein synthesis in 36 young men. That is a laboratory marker; sleep quality and performance were not measured. Cold water immersion after exercise and sleepMixed findingsTwo tiny trials gave different answers, and a review found no effect on sleep or performance. Cold exposure has its own risks. Caffeine timing and the sleep that followsModerate certaintyCaffeine late in the day cut sleep time by about 45 minutes across 24 studies. Even 400 mg taken 6 hours before bed disrupted sleep in one trial. How well sleep trackers measure sleep compared with a sleep studyModerate certaintyTrackers are good at detecting sleep, weaker at detecting wake and only fair at sleep stages. They are not a replacement for a sleep study and no study read shows they speed recovery. Orthosomnia: worry caused by tracking sleepNot enough evidenceCase reports describe worry about sleep that comes from tracker data. How common it is has not been measured. Recognising overtraining and incomplete recoveryNot enough evidenceA 2013 consensus describes overtraining as long-lasting tiredness, falling performance and low mood, and says no single marker or tracker score is reliable. See a doctor to rule out other causes.

Benefits, one by one

Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.

Sleep loss and athletic performance

Moderate certainty

Two large reviews of studies found that going without enough sleep lowers exercise performance, most clearly after a whole night awake or after waking much earlier than usual. Performance in the afternoon fell more than in the morning. What happens after a smaller loss over one to three nights is still unclear.

3 studiesStudies compared sleep of 6 hours or less in 24 hours with normal sle…

Studies, doses and limits

What the trials found

A 2022 review pooled 69 publications and found an average fall of 7.56% in exercise performance after sleep loss, about 0.4% for each hour awake before the task. A 2024 review of 27 studies in athletes found an overall effect size of -0.56, largest for waking early and for high-intensity intermittent exercise. A 2020 expert consensus agrees that a night or more without sleep reduces performance but calls partial restriction over one to three nights unclear.

Results

Sleep loss lowers performance. How much depends on the type of loss, the task and the time of day. This is a harm of too little sleep, not a treatment.

Effect sizes as reported

Mean change -7.56% (95% CI -11.9 to -3.13); effect size -0.56 in athletes.

Why this rating

Moderate because two pooled reviews agree on direction and the consensus statement agrees too, but heterogeneity is very high (I2 98%), most participants were male and tasks were laboratory tests.

Form and dose studied

Studies compared sleep of 6 hours or less in 24 hours with normal sleep, or a full night awake. These are study conditions, not advice.

Who was studied

Mostly young men and athletes, healthy; results are group averages.

Limits

Very high heterogeneity; mainly men; laboratory tasks may not match real competition; says little about a single short night.

Why researchers looked

Athletes often sleep too little because of training, travel and stress, so researchers asked how much a short night costs in performance.

Proposed mechanism Proposed mechanism

Not shown by the reviews read; they measured performance, not mechanisms. Proposed explanations include higher perceived effort and slower reactions.

A proposed mechanism does not show that the effect happens in people.

No harm from the studies, which tested sleep loss. Sleep loss itself raises safety risks such as drowsy driving: see the Safety tab.

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Sleep and sports injury in young athletes

Low certainty

In studies of teenage athletes, those who slept less were more likely to be injured. One school study found about 1.7 times the odds of injury for athletes sleeping under 8 hours a night, and a review of seven studies found 1.58 times the odds for chronic poor sleep. These are links, not proof that more sleep prevents injury.

2 studiesSelf-reported hours of sleep per night, not a product or a programme.

Studies, doses and limits

What the trials found

A 2014 survey of 112 adolescent athletes at one school (mean age 15) linked sleeping under 8 hours with 1.7 times the odds of injury. A 2019 review of 7 studies in people aged 19 or younger found chronic poor sleep went with higher odds of sports and musculoskeletal injury (odds ratio 1.58); the effect of one bad night could not be decided.

Results

A consistent link in observational studies of teenagers; no trial showed that extra sleep lowers injury.

Effect sizes as reported

Odds ratio 1.7 (95% CI 1.0 to 3.0) in the school study; 1.58 (1.05 to 2.37) pooled.

Why this rating

Low because the studies are observational, sleep was self-reported, the pooled analysis has only seven studies and there is no trial of extra sleep and injury.

Form and dose studied

Self-reported hours of sleep per night, not a product or a programme.

Who was studied

Adolescents aged 12 to 19, school and club athletes. Adult athletes were not covered by these two papers.

Limits

Observational; injury and sleep definitions differ; other differences between sleepy and rested students may explain the link.

Why researchers looked

Coaches and parents wanted to know whether tired young athletes get hurt more often.

Proposed mechanism Proposed mechanism

Not studied in these papers. Proposed: tiredness slows reactions and coordination.

A proposed mechanism does not show that the effect happens in people.

Nothing harmful found. Teenagers who are very tired or injured often should be seen by a clinician.

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Sleep extension (sleeping longer) before or during training

Low certainty

Sleep extension means deliberately spending more time in bed for several nights. Two reviews of small studies found it was the most useful sleep strategy for later performance, but the evidence is thin. A small trial in 12 men found longer sleep let them hold a muscle effort about 4% to 8% longer, mostly because it felt easier.

4 studiesStudies added about 26 to 106 minutes of sleep or time in bed; report…

Studies, doses and limits

What the trials found

A 2018 review of 10 studies (218 people aged 18 to 24) found sleep extension had the most beneficial effects on later performance. A 2021 review could include only 2 studies and called its conclusion tentative; six of fifteen measures showed a large effect. A 2023 review of 25 intervention studies again found sleep extension and naps most effective. A 2016 crossover trial of 12 men (9.8 versus 8.2 hours in bed for six nights) found time to exhaustion 3.9% longer, and 8.1% longer after one night without sleep.

Results

Promising but based on very few and small studies, mostly in young adults.

Effect sizes as reported

Time to exhaustion +3.9% and +8.1%; extension added 26 to 106 minutes in the reviewed studies.

Why this rating

Low because the reviews rest on 2 to 10 small studies, risk of bias was high in the randomised trial and quality ranged from very low to moderate.

Form and dose studied

Studies added about 26 to 106 minutes of sleep or time in bed; reported only as what was studied.

Who was studied

Young athletes and healthy young men; not older adults or casual exercisers.

Limits

Few and small studies; tests were short; the trial in men used a single muscle task; it is not clear who can actually sleep longer on request.

Why researchers looked

If too little sleep hurts performance, sleeping longer might help, so researchers tested extra sleep in athletes.

Proposed mechanism Proposed mechanism

A 2016 trial found muscle activation did not differ, and the benefit was probably lower perceived effort. This is a finding of one small trial.

A proposed mechanism does not show that the effect happens in people.

No harms were reported in the abstracts. Needing much more sleep than usual can itself be a reason to see a doctor.

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Daytime napping

Low certainty

A 2023 review of 22 randomised trials found that a daytime nap, especially 30 to under 60 minutes, improved thinking and physical test results and reduced tiredness. All of the 291 participants were young men and the tests were short, so it is not yet clear how far this applies to everyone.

3 studiesSingle daytime naps, most often at 14:00, of 30 to under 60 minutes i…

Studies, doses and limits

What the trials found

The review pooled 22 trials of naps taken between 12:30 and 16:50 (most often 14:00) by trained athletes and active adults aged 18 to 35. After a normal night, naps improved cognitive performance (SMD 0.69) and physical performance (SMD 0.99) and cut perceived fatigue (SMD -0.76). Results were similar after partial sleep deprivation. Naps of 30 to under 60 minutes and a gap of over an hour between waking and the test worked best. The 2023 sleep-intervention review also found naps among the most effective strategies, while the 2020 consensus said napping needs more research.

Results

Large average effects in short tests; heterogeneity is high and only men were studied.

Effect sizes as reported

SMD 0.99 for physical performance (95% CI 0.67 to 1.31); heterogeneity I2 about 70% to 90%.

Why this rating

Low because the pooled effect is large but inconsistent between trials (I2 up to 89%), all participants were men and the trials were small.

Form and dose studied

Single daytime naps, most often at 14:00, of 30 to under 60 minutes in the best results. Reported as studied, not advice.

Who was studied

Men aged 18 to 35, trained athletes and active adults. No women, older adults or children.

Limits

All-male samples; short laboratory tests; does not say whether a late nap harms night sleep; the NHS advises against napping for people with insomnia.

Why researchers looked

Athletes often miss sleep at night, so a nap is a convenient way to try to catch up.

Proposed mechanism Proposed mechanism

Not examined in the review. Proposed: a nap clears tiredness for a time.

A proposed mechanism does not show that the effect happens in people.

The review reported no harm. Needing long naps every day can be a sign of poor night sleep or a sleep disorder: see the Safety tab.

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Exercise in the evening and the sleep that follows

Low certainty

Many people are told not to train late in the day. A 2019 review of 23 studies found a single evening session did not hurt sleep on average and slightly increased deep sleep. Very hard exercise finishing within about an hour of bedtime might still make it harder to sleep. The NHS advice for insomnia is more cautious, so this is not settled.

2 studiesSingle sessions of evening exercise of varied intensity; the review d…

Studies, doses and limits

What the trials found

The 2019 pooled analysis of 23 studies in healthy adults found evening exercise lengthened REM latency by 7.7 minutes, increased slow-wave sleep by 1.3 percentage points and reduced stage 1 sleep by 0.9 points. Sleep onset, total sleep time and sleep efficiency might be affected after vigorous exercise ending one hour or less before bed. The NHS insomnia page advises not exercising for at least 4 hours before bed for people with insomnia.

Results

On average evening exercise did not harm sleep in healthy adults; individual and very hard late sessions may differ.

Effect sizes as reported

REM latency +7.7 min; slow-wave sleep +1.3 points.

Why this rating

Low because sleep changes were small, moderator effects disappeared when one study was removed, and the agency advice differs.

Form and dose studied

Single sessions of evening exercise of varied intensity; the review did not give a recommended time.

Who was studied

Healthy adults in single-session studies.

Limits

Single sessions only; not a hard training block; healthy people; the NHS advice for people with insomnia is more cautious.

Why researchers looked

Training late is common for working adults and athletes, so people want to know whether it harms the sleep that is needed for recovery.

Proposed mechanism Proposed mechanism

Proposed: exercise raises body temperature, which must fall again before sleep. The review found higher temperature at bedtime went with poorer sleep, but this result did not survive removal of one study.

A proposed mechanism does not show that the effect happens in people.

If hard late training keeps you awake, move it earlier. If sleep stays poor for months, see a doctor.

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Tart cherry juice and sleep

Very low certainty

Two small trials found tart cherry juice linked to longer sleep: a one-week crossover trial in 20 healthy adults and a two-week pilot in 8 older adults with insomnia. Both are very small, so this is a hint worth testing, not an answer. A separate review found tart cherry may ease soreness after hard exercise, which is not the same as better sleep.

3 studiesJuice concentrate or 240 mL of juice twice a day, as the trials used.…

Studies, doses and limits

What the trials found

In 20 healthy volunteers, a week of tart cherry juice concentrate raised urinary melatonin and improved time in bed, total sleep time and sleep efficiency by actigraphy. In 8 older adults with insomnia, juice taken for two weeks lengthened polysomnography sleep by 84 minutes, but four of five questionnaires showed no difference. A 2021 review of 14 studies found small to moderate gains in soreness and strength recovery, not sleep.

Results

Hint of benefit in two tiny trials; no trial in athletes with a sleep outcome was read.

Effect sizes as reported

Sleep time +84 minutes in the older-adult pilot (8 completers).

Why this rating

Very low because the trials had 20 and 8 completers, were short, measured sleep differently and did not include athletes.

Form and dose studied

Juice concentrate or 240 mL of juice twice a day, as the trials used. Not advice; juice contains sugar.

Who was studied

Healthy adults and adults over 50 with insomnia.

Limits

Tiny samples; one used actigraphy; no athlete sleep data; juice sugar and calories not addressed in the abstracts.

Why researchers looked

Tart cherries contain melatonin and plant chemicals, and athletes already use them for recovery, so researchers tested sleep too.

Proposed mechanism Proposed mechanism

Proposed: the melatonin in the juice, and in the older adult pilot an effect on tryptophan breakdown shown in cell experiments. Not shown in humans.

A proposed mechanism does not show that the effect happens in people.

Three people with sleep apnea were excluded and referred in the pilot, a reminder to see a doctor if you snore and are always tired.

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Magnesium supplements and sleep

Very low certainty

A 2021 review of three small trials in older adults with insomnia found magnesium shortened the time to fall asleep by about 17 minutes. The trials were weak and none involved athletes, so the review calls the evidence too limited to make firm recommendations. No trial read tested magnesium for sleep in athletes or for exercise recovery.

1 studiesThe authors say trials used less than 1 g, up to three times a day. R…

Studies, doses and limits

What the trials found

Three randomised trials (151 older adults) compared oral magnesium with placebo. Time to fall asleep was 17.36 minutes shorter and total sleep time 16.06 minutes longer, but the sleep-time difference was not statistically significant. Quality was low to very low.

Results

Small possible benefit in older adults with insomnia; unknown for athletes and younger adults.

Effect sizes as reported

Sleep onset latency -17.36 min (95% CI -27.27 to -7.44).

Why this rating

Very low because there were only three small trials at moderate-to-high risk of bias in older adults with insomnia, not athletes.

Form and dose studied

The authors say trials used less than 1 g, up to three times a day. Reported as studied, not advice.

Who was studied

Older adults with insomnia in three countries.

Limits

Three small trials; high risk of bias; a different population from athletes.

Why researchers looked

Magnesium is a popular evening supplement for sleep and cramps, so researchers pooled the few trials.

Proposed mechanism Proposed mechanism

Not examined in the review.

A proposed mechanism does not show that the effect happens in people.

Ask a doctor or pharmacist first if you take medicines or have kidney problems (general guidance, not from a source read). See the Safety tab.

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Protein before bed for overnight muscle recovery

Not enough evidence

In a trial of 36 young men, 45 g of casein or whey protein taken before sleep after evening endurance exercise increased overnight muscle protein synthesis compared with a placebo drink. This is a laboratory marker of muscle building. The trial did not measure sleep quality, soreness or performance, so it does not prove better recovery.

1 studies45 g of protein 30 minutes before sleep, as studied. Not advice.

Studies, doses and limits

What the trials found

Thirty-six healthy young men did an endurance session at 19:45, then took casein, whey or placebo 30 minutes before sleep. Mitochondrial synthesis was 0.087 versus 0.067 %/h and myofibrillar 0.060 versus 0.047 %/h, with no difference between casein and whey.

Results

Raises a lab marker overnight; no performance or sleep result.

Effect sizes as reported

Protein vs placebo: 0.087 vs 0.067 %/h (mitochondrial), 0.060 vs 0.047 %/h (myofibrillar).

Why this rating

Insufficient for recovery or performance because only a laboratory marker was measured, in one night in young men.

Form and dose studied

45 g of protein 30 minutes before sleep, as studied. Not advice.

Who was studied

Healthy young men.

Limits

One night; a marker, not an outcome; the effect on sleep itself was not measured.

Why researchers looked

Sleep is a long fast, so researchers asked whether a drink before bed helps muscles rebuild overnight.

Proposed mechanism Proposed mechanism

The trial shows the protein reached muscle and raised synthesis rates. Whether that changes performance was not tested.

A proposed mechanism does not show that the effect happens in people.

Large protein amounts can matter for people with kidney disease (general guidance, not from a source read); ask a doctor first.

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Cold water immersion after exercise and sleep

Mixed findings

Results are mixed. A trial in 11 cyclists found no change in sleep after evening exercise with or without a cold bath. A trial in 12 runners found that whole-body immersion including the head went with more deep sleep and less movement early in the night, with no change in muscle recovery markers. The 2023 sleep-intervention review found no effect on sleep or performance, based on few studies.

3 studiesCold water at about 13 C for 10 minutes, as one trial used. Not advic…

Studies, doses and limits

What the trials found

In the cyclist trial (11 men, polysomnography) no whole-night sleep measure differed. In the runner trial (12 men, 13.3 C for 10 minutes) whole-body immersion lowered arousals and limb movement and raised the share of slow-wave sleep in the first part of the night, but fatigue and muscle damage markers did not change over 48 hours.

Results

Different results in two tiny trials, and a review that found no benefit.

Effect sizes as reported

No effect size reported in the abstracts.

Why this rating

Mixed because one trial found no effect and the other found changes in some sleep measures, both with 11 to 12 men.

Form and dose studied

Cold water at about 13 C for 10 minutes, as one trial used. Not advice.

Who was studied

Trained male cyclists and runners.

Limits

Eleven and twelve men; one night each; better sleep stages were not shown to improve recovery.

Why researchers looked

Cold baths are popular for recovery, and cooling the body might help sleep, so researchers measured sleep after them.

Proposed mechanism Proposed mechanism

Proposed: cold lowers body temperature, which may help deep sleep. The runner trial measured lower core temperature after whole-body immersion.

A proposed mechanism does not show that the effect happens in people.

Cold exposure carries its own risks; see the Cold and heat exposure page. Do not use it alone in water or with a heart condition without medical advice (general guidance).

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Caffeine timing and the sleep that follows

Moderate certainty

This one is about harm, and it is fairly clear. A 2023 review of 24 studies found caffeine cut total sleep time by about 45 minutes and sleep efficiency by 7%. A trial found 400 mg of caffeine hurt sleep even when taken 6 hours before bed. The review estimated that coffee is best finished about 9 hours before bed and a pre-workout drink about 13 hours before.

3 studiesThe trial used 400 mg; the examples in the review are coffee at 107 m…

Studies, doses and limits

What the trials found

The review pooled 24 studies: total sleep time -45 minutes, sleep efficiency -7%, time to fall asleep +9 minutes, wake after sleep onset +12 minutes and deep sleep -11.4 minutes. It estimated that coffee (107 mg per 250 mL) should be consumed at least 8.8 hours before bed and a pre-workout serve (217.5 mg) at least 13.2 hours before. A randomised trial of 400 mg at 0, 3 or 6 hours before bed found each timing disrupted sleep.

Results

Late caffeine reduces sleep; the review gives timing estimates for the average adult.

Effect sizes as reported

Total sleep time -45 min; sleep efficiency -7%.

Why this rating

Moderate because a 24-study meta-analysis and a randomised trial agree, but doses and timing vary and people differ in sensitivity.

Form and dose studied

The trial used 400 mg; the examples in the review are coffee at 107 mg per 250 mL and a pre-workout serve of 217.5 mg. The timing numbers are model estimates, not advice.

Who was studied

Adults in the studies; the abstracts give few details.

Limits

Timing figures are averages; sensitivity differs; caffeine in pre-workout products varies.

Why researchers looked

Athletes use caffeine to train, and pre-workout drinks are often taken late, so researchers asked what that costs in sleep.

Proposed mechanism Proposed mechanism

Proposed: caffeine blocks the brain signals that build sleepiness. The abstracts did not test this.

A proposed mechanism does not show that the effect happens in people.

The FDA cites 400 mg a day as an amount not generally associated with negative effects in most adults, with wide differences in sensitivity. Ask a clinician if you are pregnant, have a heart condition or take medicines.

^{10 8 26}

How well sleep trackers measure sleep compared with a sleep study

Moderate certainty

Consumer trackers are good at telling that you are asleep but weak at telling that you are awake, and they are only fair at guessing sleep stages. A 2025 review of 24 studies found wrist-worn trackers differ from polysomnography on total sleep time, efficiency and time awake. No study read shows that wearing a tracker, by itself, speeds recovery.

3 studiesWrist-worn, ring, bedside and phone-based devices were tested; no pro…

Studies, doses and limits

What the trials found

A laboratory study of seven devices in 34 healthy young adults found high sensitivity (0.93 or higher) but low specificity (0.18 to 0.54) for wake. A 2025 meta-analysis of 24 studies (798 people) found significant differences from polysomnography in total sleep time, sleep efficiency, sleep latency and wake after sleep onset. A 2023 study of 11 devices in 75 people found stage agreement scores from 0.26 to 0.69.

Results

Useful for rough patterns, not for precise sleep stages or for judging recovery.

Effect sizes as reported

Sensitivity 0.93 or higher, specificity 0.18 to 0.54; sleep-stage macro F1 0.26 to 0.69.

Why this rating

Moderate because three studies of different designs agree on the broad picture, but devices and models change quickly and most users were healthy adults.

Form and dose studied

Wrist-worn, ring, bedside and phone-based devices were tested; no product is recommended here.

Who was studied

Healthy young adults, plus people referred for sleep tests.

Limits

Devices are updated often; study populations are not athletes; scores such as sleep score or readiness are proprietary and were not tested here.

Why researchers looked

Many athletes and people who exercise use a watch or ring score to decide how hard to train, so researchers compared them with a hospital sleep study.

Proposed mechanism Proposed mechanism

Trackers estimate sleep from movement and heart-rate signals; they do not record brain waves the way a sleep study does.

A proposed mechanism does not show that the effect happens in people.

A tracker cannot diagnose sleep apnea or insomnia. See a doctor for loud snoring with gasping or heavy daytime sleepiness.

^{5 15 14}

Orthosomnia: worry caused by tracking sleep

Not enough evidence

Orthosomnia is a name for worry about sleep that comes from looking at tracker data, sometimes leading people to chase perfect sleep and sleep worse. The evidence is a clinic case report series, so we do not know how common it is. The authors suggest bringing trackers into cognitive behavioural therapy for insomnia.

1 studiesNot a product or dose. Advice from the authors is to include trackers…

Studies, doses and limits

What the trials found

A 2017 case report series from a sleep clinic described patients seeking treatment for problems seen on trackers, often trusting the device over validated methods. A later editorial in 2023 discusses the idea but has no abstract to read.

Results

Described in cases, not measured in a study with a comparison group.

Effect sizes as reported

No effect size.

Why this rating

Insufficient because it rests on case reports with no count of how often it happens.

Form and dose studied

Not a product or dose. Advice from the authors is to include trackers in CBT-I.

Who was studied

Clinic patients.

Limits

No prevalence data; no trial of how to prevent or treat it.

Why researchers looked

Clinicians noticed patients arriving with tracker charts and fears about light sleep.

Proposed mechanism Proposed mechanism

Proposed: checking data increases worry and effort to sleep, which keeps people awake.

A proposed mechanism does not show that the effect happens in people.

If checking a tracker makes sleep or training worse, stop for a while and talk to a doctor; CBT-I is listed first for chronic insomnia by guidelines (see our Insomnia page).

Recognising overtraining and incomplete recovery

Not enough evidence

Overtraining syndrome means feeling worse and performing worse for a long time after too much training and too little recovery. It can look like many other problems, so a 2013 consensus statement says other causes must be ruled out first and that no single test or tracker marker meets all criteria.

1 studiesNot a product. Training load, sleep and nutrition are discussed in ge…

Studies, doses and limits

What the trials found

The consensus separates functional overreaching (short dip, then gain), non-functional overreaching and overtraining syndrome. Symptoms named include fatigue, performance decline and mood disturbance. Causes to exclude include infection, organic disease, low energy intake, too little carbohydrate or protein, iron or magnesium deficiency and allergies. Markers such as hormones, performance and psychological tests are used but none is generally accepted.

Results

A definition and a safe approach, not a test: no marker is reliable enough on its own.

Effect sizes as reported

No effect size.

Why this rating

Insufficient for any single sign or tracker score because the consensus states no marker meets all criteria and gives no pooled numbers.

Form and dose studied

Not a product. Training load, sleep and nutrition are discussed in general terms.

Who was studied

Athletes.

Limits

Consensus statement, 2013; abstract-level reading only; sleep is not singled out in the abstract.

Why researchers looked

Athletes and keen exercisers sometimes push through tiredness, so a clear definition and safety net matter.

Proposed mechanism Proposed mechanism

The consensus describes prolonged maladaptation of several biological, nerve and hormone systems but notes the cause is not fully understood.

A proposed mechanism does not show that the effect happens in people.

Long-lasting tiredness, falling performance or low mood is a reason to see a doctor and rule out illness, not to take more supplements.

¹⁸

Connections to the rest of health

How Sleep and Exercise Recovery: What Is Known connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.

Explore every connection: goals, body systems, organs, symptoms, genes

Kind of connection Connected to Search

A. Wellness goals

Connected to	Evidence status	Context	Studies
Better Sleep	Moderate certainty	Sleep loss and athletic performance: Two large reviews of studies found that going without enough sleep lowers exercise performance, most clearly after a whole night awake or after waking much earlier than usual. Performance in the afternoon fell more than in the morning. What happens after a smaller loss over one to three nights is still unclear. Daytime napping: A 2023 review of 22 randomised trials found that a daytime nap, especially 30 to under 60 minutes, improved thinking and physical test results and reduced tiredness. All of the 291 participants were young men and the tests were short, so it is not yet clear how far this applies to everyone.	^{6 11 25 19 7 23 29 17 10 8 26}
Better Sleep	Low certainty	Sleep and sports injury in young athletes: In studies of teenage athletes, those who slept less were more likely to be injured. One school study found about 1.7 times the odds of injury for athletes sleeping under 8 hours a night, and a review of seven studies found 1.58 times the odds for chronic poor sleep. These are links, not proof that more sleep prevents injury.	^{20 9}
Better Sleep	Low certainty	Sleep extension (sleeping longer) before or during training: Sleep extension means deliberately spending more time in bed for several nights. Two reviews of small studies found it was the most useful sleep strategy for later performance, but the evidence is thin. A small trial in 12 men found longer sleep let them hold a muscle effort about 4% to 8% longer, mostly because it felt easier.	^{3 22 7 1}
Better Sleep	Very low certainty	Tart cherry juice and sleep: Two small trials found tart cherry juice linked to longer sleep: a one-week crossover trial in 20 healthy adults and a two-week pilot in 8 older adults with insomnia. Both are very small, so this is a hint worth testing, not an answer. A separate review found tart cherry may ease soreness after hard exercise, which is not the same as better sleep. Cold water immersion after exercise and sleep: Results are mixed. A trial in 11 cyclists found no change in sleep after evening exercise with or without a cold bath. A trial in 12 runners found that whole-body immersion including the head went with more deep sleep and less movement early in the night, with no change in muscle recovery markers. The 2023 sleep-intervention review found no effect on sleep or performance, based on few studies.	^{13 16 12 21 4 7}
Sleep Quality	Not enough evidence	Protein before bed for overnight muscle recovery: In a trial of 36 young men, 45 g of casein or whey protein taken before sleep after evening endurance exercise increased overnight muscle protein synthesis compared with a placebo drink. This is a laboratory marker of muscle building. The trial did not measure sleep quality, soreness or performance, so it does not prove better recovery.	²⁴
Sleep Quality	Moderate certainty	How well sleep trackers measure sleep compared with a sleep study: Consumer trackers are good at telling that you are asleep but weak at telling that you are awake, and they are only fair at guessing sleep stages. A 2025 review of 24 studies found wrist-worn trackers differ from polysomnography on total sleep time, efficiency and time awake. No study read shows that wearing a tracker, by itself, speeds recovery.	^{5 15 14}
Stress Anxiety	Not enough evidence	Orthosomnia: worry caused by tracking sleep: Orthosomnia is a name for worry about sleep that comes from looking at tracker data, sometimes leading people to chase perfect sleep and sleep worse. The evidence is a clinic case report series, so we do not know how common it is. The authors suggest bringing trackers into cognitive behavioural therapy for insomnia.	²
Energy Fatigue	Not enough evidence	Recognising overtraining and incomplete recovery: Overtraining syndrome means feeling worse and performing worse for a long time after too much training and too little recovery. It can look like many other problems, so a 2013 consensus statement says other causes must be ruled out first and that no single test or tracker marker meets all criteria.	¹⁸

B. Body systems

Connected to	Kind of connection	Evidence status	Context	Studies
Sleep Recovery	Biological association	Moderate certainty	Studied for: Sleep loss and athletic performance Studied for: Sleep and sports injury in young athletes	^{6 11 25 20 9 3 22 7 1 19 23 29 13 16 12 17 21 4 10 8 26}
Musculoskeletal System	Biological association	Not enough evidence	Studied for: Protein before bed for overnight muscle recovery	²⁴
Nervous System	Biological association	Moderate certainty	Studied for: How well sleep trackers measure sleep compared with a sleep study	^{5 15 14}
Stress Mood	Biological association	Not enough evidence	Studied for: Orthosomnia: worry caused by tracking sleep	²
Whole Body	Biological association	Not enough evidence	Studied for: Recognising overtraining and incomplete recovery	¹⁸

E. Health conditions

Connected to	Kind of connection	Evidence status	Context	Studies
Sleep apnea		Health agency guidance	Loud snoring, gasping and heavy daytime sleepiness need a sleep test; a tracker cannot rule it out. Loud snoring with gasping and heavy daytime sleepiness need a sleep test, not a tracker. Preparation or compound: Tracker or sleep tip used instead of a sleep test	^{30 27}
Insomnia		Health agency guidance	Long-lasting poor sleep deserves care; CBT-I is the usual first step. Preparation or compound: Tracker-driven worry and sleep aids	^{29 2}

I. Biomarkers

Connected to	Kind of connection	Evidence status	Context	Studies
Exercise performance tests	Biological association	Moderate certainty	Measured in trials: lower after sleep loss; higher after sleep extension and naps in small studies. A lab change is not the same as a health benefit.	^{6 19}
Sports or muscle-and-joint injury	Biological association	Low certainty	Measured in trials: higher in adolescents who sleep less. A lab change is not the same as a health benefit.	^{9 20}
Total sleep time and sleep efficiency	Biological association	Moderate certainty	Measured in trials: lower after late caffeine; mixed or small with tart cherry and magnesium. A lab change is not the same as a health benefit.	^{10 13}
Tracker agreement with polysomnography	Biological association	Moderate certainty	Measured in trials: high for sleep, low for wake, variable for sleep stages. A lab change is not the same as a health benefit.	^{5 14 15}

L. Active compounds

Connected to	Kind of connection	Evidence status	Context	Studies
Caffeine	Biological association	Human	Reduces sleep time and efficiency when taken late in the day.	^{10 8 26}
Tart cherry (Montmorency) juice	Biological association	Human	Studied for sleep in two small trials and for exercise soreness in a review.	^{13 16 12}
Magnesium	Biological association	Human	Possible shorter time to fall asleep in older adults with insomnia.	¹⁷
Casein and whey protein	Biological association	Human	Raised overnight muscle protein synthesis in a laboratory trial.	²⁴

Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 31, 2026).

Evidence at a glance: what the research found for 13 outcomes

3Moderate certainty

4Low certainty

2Very low certainty

1Mixed findings

3Not enough evidence

Each outcome below is one thing researchers measured. Certainty is how far the evidence can be trusted, not how well it works. The full studies are on the next tab.

Sleep loss and athletic performance 3 studies Moderate certainty Sleep and sports injury in young athletes 2 studies Low certainty Sleep extension (sleeping longer) before or during training 4 studies Low certainty Daytime napping 3 studies Low certainty Exercise in the evening and the sleep that follows 2 studies Low certainty Tart cherry juice and sleep 3 studies Very low certainty Magnesium supplements and sleep 1 study Very low certainty Protein before bed for overnight muscle recovery 1 study Not enough evidence Cold water immersion after exercise and sleep 3 studies Mixed findings Caffeine timing and the sleep that follows 3 studies Moderate certainty How well sleep trackers measure sleep compared with a sleep study 3 studies Moderate certainty Orthosomnia: worry caused by tracking sleep 1 study Not enough evidence Recognising overtraining and incomplete recovery 1 study Not enough evidence

The evidence

The research centre for Sleep and Exercise Recovery: What Is Known. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.

Evidence by outcome

Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).

How we rate evidence

High certainty

Several well-run trials or reviews agree; further research is unlikely to change the picture much.

Moderate certainty

Good trials point the same way, but some doubt remains.

Low certainty

Small, short or inconsistent trials. The finding could change with better research.

Very low certainty

Very little or very weak human data. Treat as a possibility only.

Mixed findings

Trials or reviews disagree with each other.

Not enough evidence

Not enough human research to say either way.

Evidence against

Good research found no benefit, or found harm.

We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We searched PubMed, re-read the abstract of every review, trial and consensus statement cited, and read the NHS, NHLBI and FDA pages in full. Full texts of the papers were not read. Certainty ratings are the compiler's own reading. Funding is not stated in most abstracts, and this is noted where relevant.

Study library: every study we checked 30

Design Research type Year from Search

Study	Design	People	Product, dose, length	Result
Arnal 2016 Sleep Extension before Sleep Loss: Effects on Performance and Neuromuscular Function. Med Sci Sports Exerc · PMID 27015382 · DOI	Randomised crossover trial	12 Twelve healthy men (not described as athletes in the abstract)	Six nights of sleep extension at home, followed by one night of total sleep deprivation About 9.8 hours in bed (extended) versus 8.2 hours (habitual) per night Six nights, then 34 to 37 hours awake · vs Habitual sleep (8.2 hours in bed)	Time to exhaustion was longer after the extended nights (+3.9% at baseline and +8.1% after the sleepless night). Performance fell after the sleepless night either way (-7.2% after habitual sleep and -3.7% after extension). Perceived effort was lower after extension following sleep loss. Muscle activation did not differ, so the benefit was probably due to lower perceived effort. Time to exhaustion +3.9% (baseline) and +8.1% (after sleep deprivation) with extension (Not given in the abstract) Methods, limits and funding Outcomes: Time to exhaustion in a knee-extension hold; neuromuscular tests; perceived effort Limitations: Twelve men, one muscle task, laboratory setting; not a sport-specific result. Funding and conflicts: Research support from a non-US-government source is listed in the PubMed record; no conflict-of-interest statement in the record read. Read: abstract
Baron 2017 Orthosomnia: Are Some Patients Taking the Quantified Self Too Far? J Clin Sleep Med · PMID 27855740 · DOI	Case reports	Patients at a sleep clinic who sought treatment for problems seen on a sleep tracker (case reports)	Wearable sleep tracking	The authors describe patients who seek treatment because of light or restless sleep shown on a tracker, and who may chase perfect sleep. These patients often trust the tracker more than validated methods. The authors call this orthosomnia and suggest including trackers in cognitive behavioural therapy for insomnia. Methods, limits and funding Outcomes: Clinical observations of tracker-driven worry about sleep Limitations: Case reports only: no count of how common it is and no comparison group. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Bonnar 2018 Sleep Interventions Designed to Improve Athletic Performance and Recovery: A Systematic Review of Current Approaches. Sports Med · PMID 29352373 · DOI	Systematic review	10 studies, 218 participants aged 18 to 24 (swimming, soccer, basketball, tennis and others)	Sleep extension, napping, sleep hygiene and post-exercise recovery strategies Varied by study Varied by study · vs Habitual sleep or control	Sleep extension had the most beneficial effects on later performance. The review concludes that sleep plays a role in some but not all aspects of performance and recovery. Methods, limits and funding Outcomes: Subsequent performance and recovery Limitations: Small studies in young competitive athletes; study quality was scored on a modified scale; a 2016 search updated to 2017. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Chauvineau 2021 Effect of the Depth of Cold Water Immersion on Sleep Architecture and Recovery Among Well-Trained Male Endurance Runners. Front Sports Act Living · PMID 33870188 · DOI	Randomised crossover trial	12 Twelve well-trained male endurance runners	Cold water immersion at 13.3 C for 10 minutes after evening running (whole body with head, or up to the hip) 10 minutes at 13.3 C Single evening session, then polysomnography · vs Out-of-water rest	Whole-body immersion (including the head) was followed by less arousal, less limb movement and a higher proportion of deep slow-wave sleep early in the night than the other conditions. There were no differences in fatigue or muscle damage markers over 48 hours. Methods, limits and funding Outcomes: Sleep architecture by polysomnography; fatigue and muscle damage markers to 48 hours Limitations: Twelve men; the control group had 10; no evidence that the sleep changes improved recovery; only one night studied. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Chinoy 2021 Performance of seven consumer sleep-tracking devices compared with polysomnography. Sleep · PMID 33378539 · DOI	Validation study against polysomnography	34 Thirty-four healthy young adults (22 women), three nights in a sleep laboratory including a disrupted-sleep night	Seven consumer sleep trackers (four wearable, three nearable) and an actigraph Three nights · vs Polysomnography	The trackers were very good at detecting sleep (sensitivity 0.93 or higher) but poor at detecting wake (specificity 0.18 to 0.54). Stage comparisons were mixed or inconsistent and devices did worse on disrupted nights. Sensitivity 0.93 or higher; specificity 0.18 to 0.54 (Not given in the abstract) Methods, limits and funding Outcomes: Epoch-by-epoch agreement for sleep versus wake, and sleep stages Limitations: Healthy young adults for three nights; devices tested are older models; results may differ in other people. Funding and conflicts: US government (non-NIH) research support is listed in the PubMed record; no conflict statement in the record read. Read: abstract
Craven 2022 Effects of Acute Sleep Loss on Physical Performance: A Systematic and Meta-Analytical Review. Sports Med · PMID 35708888 · DOI	Systematic review meta analysis	69 publications (227 outcome measures); 89% of participants were male	Acute sleep loss (deprivation, early or late restriction, sleep of 6 hours or less in 24 hours) Sleep of 6 hours or less in 24 hours versus more than 6 hours One night or less (acute) · vs Normal sleep (more than 6 hours in 24 hours)	Sleep loss lowered exercise performance on average, in every exercise category. The effect was consistent after total deprivation and after late restriction (waking earlier than normal) but not after early restriction (going to sleep later). Performance fell by about 0.4% for every hour awake before the task. Afternoon and evening tasks were hit consistently; morning tasks were largely unaffected. Mean change -7.56% in performance (95% CI -11.9 to -3.13; I2 98.1%) Methods, limits and funding Outcomes: Percentage change in exercise performance (anaerobic power, speed/power endurance, high-intensity intervals, strength, endurance, strength-endurance, skill) Limitations: Very high heterogeneity between studies; mostly male and mostly laboratory tasks; the abstract gives no funding statement. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Cunha 2023 The Impact of Sleep Interventions on Athletic Performance: A Systematic Review. Sports Med Open · PMID 37462808 · DOI	Systematic review	25 intervention studies (2011 to 2021) in athletes of individual and team sports	Sleep hygiene, naps, sleep extension, light changes, cold water immersion, mindfulness, or combinations Varied by study Varied by study · vs Control conditions in each study	Sleep extension and naps were the most representative and effective strategies for improving sleep and performance. Mindfulness and light changes looked promising but need more studies. Sleep hygiene, removing electronic devices at night and cold water immersion showed no effect on sleep and performance or recovery, based on few studies only. The authors acknowledge limited high-quality evidence. Methods, limits and funding Outcomes: Sleep and an objective performance or recovery outcome Limitations: Abstract gives no pooled numbers; "no effect" findings rest on few studies; registered with INPLASY (INPLASY202250069). Funding and conflicts: PubMed record lists a Portuguese national research funder (Fundacao para a Ciencia e a Tecnologia). Read: abstract
Drake 2013 Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. J Clin Sleep Med · PMID 24235903 · DOI	Randomised controlled trial	Adults sleeping at home (number and details not given in the abstract)	Caffeine, a single fixed dose 400 mg Taken 0, 3 or 6 hours before habitual bedtime · vs Placebo	Caffeine at bedtime, 3 hours before or 6 hours before bedtime each disrupted sleep compared with placebo. Even 6 hours before bed caused an important reduction in total sleep time. Methods, limits and funding Outcomes: Self-reported sleep and sleep measured by a validated portable monitor Limitations: Single 400 mg dose; number and description of participants not given in the abstract. Funding and conflicts: Research support from a non-US-government source is listed in the PubMed record; no conflict-of-interest statement in the record read. Read: abstract
Gao 2019 Lack of Sleep and Sports Injuries in Adolescents: A Systematic Review and Meta-analysis. J Pediatr Orthop · PMID 30888337 · DOI	Systematic review meta analysis	7 studies of adolescents aged 19 or younger	Chronic or acute lack of sleep Definitions varied by study · vs Adolescents who slept well	Five of seven studies found that adolescents who chronically slept poorly were more likely to be injured. Chronic poor sleep was linked with higher odds of injury in the pooled analysis. The effect of acute (one-off) lack of sleep could not be settled: one study found a link and one did not. Pooled odds ratio 1.58 for chronic poor sleep (95% CI 1.05 to 2.37; P=0.03) Methods, limits and funding Outcomes: Sports or musculoskeletal injury Limitations: Only seven studies, mostly observational (level IV review of level II studies); sleep and injury definitions differ; adolescents only. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Gardiner 2023 The effect of caffeine on subsequent sleep: A systematic review and meta-analysis. Sleep Med Rev · PMID 36870101 · DOI	Systematic review meta analysis	24 studies of caffeine and night-time sleep	Caffeine (coffee, pre-workout products and others) Coffee 107 mg per 250 mL; standard serve of pre-workout supplement 217.5 mg Varied by study	Caffeine reduced total sleep time by 45 minutes and sleep efficiency by 7%, increased time to fall asleep by 9 minutes and time awake in the night by 12 minutes, and reduced deep sleep by 11.4 minutes. The authors estimate that coffee should be consumed at least 8.8 hours before bedtime and a pre-workout serve at least 13.2 hours before to avoid reduced total sleep time. Total sleep time -45 min; sleep efficiency -7%; latency +9 min; wake after sleep onset +12 min (Not given in the abstract) Methods, limits and funding Outcomes: Total sleep time, sleep efficiency, sleep onset latency, wake after sleep onset, sleep stages Limitations: Doses and timing varied by study; the timing figures are model estimates for the average adult; sensitivity differs between people. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Gong 2024 Effects of Acute Sleep Deprivation on Sporting Performance in Athletes: A Comprehensive Systematic Review and Meta-Analysis. Nat Sci Sleep · PMID 39006249 · DOI	Systematic review meta analysis	27 studies, 75 indicators; athletes	Acute sleep deprivation (whole night, or partial at the start or end of the night) Not given in the abstract Acute · vs Normal sleep	Acute sleep deprivation clearly lowered athletic performance. Waking early (partial deprivation at the end of the night) hurt most; losing the first part of the night was not significant. High-intensity intermittent exercise and skill tasks were hit hardest, and performance in the afternoon fell more than in the morning. Overall effect size -0.56; whole night -0.23; end-of-night partial -1.17; start-of-night partial -0.25 (not significant); afternoon -1.11 vs morning -0.30 (Not given in the abstract) Methods, limits and funding Outcomes: Overall athletic performance and by ability (high-intensity intermittent, skill, speed, aerobic endurance, explosive power) Limitations: Abstract gives no confidence intervals, population details or heterogeneity; mix of Chinese and English studies. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Hill 2021 Tart Cherry Supplementation and Recovery From Strenuous Exercise: A Systematic Review and Meta-Analysis. Int J Sport Nutr Exerc Metab · PMID 33440334 · DOI	Systematic review meta analysis	14 studies of tart cherry supplements before or after strenuous exercise	Tart cherry supplements Varied by study Varied by study	Tart cherry reduced muscle soreness a little and helped strength and power recover. It did not significantly change creatine kinase or TNF-alpha. The review is about recovery after strenuous exercise, not sleep. Soreness ES -0.44; strength -0.78; power -0.53 (Soreness -0.87 to -0.02; strength -1.11 to -0.46) Methods, limits and funding Outcomes: Muscle soreness, strength, power, creatine kinase, inflammation markers Limitations: Different products and doses pooled; small studies; says nothing about sleep. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Howatson 2012 Effect of tart cherry juice (Prunus cerasus) on melatonin levels and enhanced sleep quality. Eur J Nutr · PMID 22038497 · DOI	Randomised crossover trial	20 Twenty healthy adult volunteers	Montmorency tart cherry juice concentrate Fruit juice concentrate Dose not given in the abstract 7 days · vs Placebo drink	Total urinary melatonin was higher with cherry juice. Time in bed, total sleep time and sleep efficiency were higher than on placebo. The authors suggest it might help with disturbed sleep. Methods, limits and funding Outcomes: Urinary melatonin metabolite; time in bed, total sleep time and sleep efficiency by wrist actigraphy; sleep questionnaires Limitations: Twenty healthy people, one week, product-specific; sleep measured by actigraphy, which is not a sleep study; healthy volunteers, not athletes or people with insomnia. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Lee 2023 Accuracy of 11 Wearable, Nearable, and Airable Consumer Sleep Trackers: Prospective Multicenter Validation Study. JMIR Mhealth Uhealth · PMID 37917155 · DOI	Validation study against polysomnography	75 Seventy-five people at a hospital and a sleep clinic in Korea	Eleven consumer sleep trackers: five wearables (including Apple Watch 8, Oura Ring 3, Fitbit Sense 2), three bedside mats or hubs, three phone apps Overnight recordings (543 hours of polysomnography) · vs Polysomnography	Agreement with polysomnography varied a lot between devices: the best macro F1 score was 0.69 and the worst 0.26. Devices differed in which stage they scored best, and results varied with body mass index, sleep efficiency and apnea-hypopnea index. Macro F1 from 0.26 to 0.69 for sleep staging (Not given in the abstract) Methods, limits and funding Outcomes: Epoch-by-epoch agreement for sleep stages (macro F1 score) Limitations: Participants were people referred for sleep testing, not athletes; devices may have been updated since Funding and conflicts: Research support from a non-US-government source is listed in the PubMed record; no conflict-of-interest statement in the record read. Read: abstract
Lee 2025 Performance of consumer wrist-worn sleep tracking devices compared to polysomnography: a meta-analysis. J Clin Sleep Med · PMID 39484805 · DOI	Systematic review meta analysis	798 24 studies with 798 participants using consumer wrist-worn devices	Fitbit, Jawbone, WHOOP, Garmin, Apple Watch and others Overnight recordings · vs Polysomnography	Wrist-worn trackers differed significantly from polysomnography on total sleep time, sleep efficiency, sleep latency and time awake after falling asleep. The authors conclude they are not as reliable as polysomnography for these key measures, though they can still be useful for tracking general patterns. Total sleep time difference -16.9 min; sleep efficiency -4.7 points; sleep latency +2.6 min; wake after sleep onset +13.3 min (Total sleep time -26.3 to -7.4 min; wake after sleep onset 4.5 to 22.0 min) Methods, limits and funding Outcomes: Total sleep time, sleep efficiency, sleep latency, wake after sleep onset Limitations: Many different devices and models pooled; devices change quickly; mostly healthy adults. Funding and conflicts: Research support from a non-US-government source is listed in the PubMed record; no conflict-of-interest statement in the record read. Read: abstract
Losso 2018 Pilot Study of the Tart Cherry Juice for the Treatment of Insomnia and Investigation of Mechanisms. Am J Ther · PMID 28901958 · DOI	Randomised crossover pilot	8 Adults over 50 with insomnia (11 randomised, 3 with sleep apnea excluded and referred, 8 completed)	Montmorency tart cherry juice Fruit juice 240 mL twice a day 2 weeks, then 2 weeks of placebo with a 2-week washout · vs Placebo drink	Eight people who completed the trial slept 84 minutes longer on polysomnography with cherry juice, and sleep efficiency on one questionnaire (PSQI) improved. The other four questionnaires showed no significant differences. Sleep time +84 minutes on polysomnography (P = 0.0182) (Not given in the abstract) Methods, limits and funding Outcomes: Sleep time and efficiency by polysomnography; five questionnaires; blood markers Limitations: Eight completers; pilot study; most questionnaires showed no difference; juice carries sugar. Funding and conflicts: PubMed record lists US NIH institute grants; no conflict statement in the record read. Read: abstract
Mah 2021 Oral magnesium supplementation for insomnia in older adults: a Systematic Review & Meta-Analysis. BMC Complement Med Ther · PMID 33865376 · DOI	Systematic review meta analysis	151 3 randomised trials in older adults with insomnia, in 3 countries	Oral magnesium supplementation Authors state under 1 g, up to three times a day, in the trials Not given in the abstract · vs Placebo or no treatment	Falling asleep took about 17 minutes less after magnesium than placebo. Total sleep time was about 16 minutes longer but this was not statistically significant. All three trials had moderate-to-high risk of bias and quality of evidence was low to very low. The authors say the literature is too weak for firm recommendations. Sleep onset latency -17.36 min; total sleep time +16.06 min (not significant) (Latency -27.27 to -7.44 min; P = 0.0006) Methods, limits and funding Outcomes: Sleep onset latency, total sleep time, adverse events Limitations: Older adults with insomnia only, not athletes; three small trials with moderate-to-high risk of bias; low-to-very-low quality evidence. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Meeusen 2013 Prevention, diagnosis, and treatment of the overtraining syndrome: joint consensus statement of the European College of Sport Science and the American College of Sports Medicine. Med Sci Sports Exerc · PMID 23247672 · DOI	Consensus statement	Athletes; expert consensus statement of the European College of Sport Science and the American College of Sports Medicine	Training overload without enough recovery (functional overreaching, nonfunctional overreaching, overtraining syndrome)	Overtraining syndrome is described as prolonged maladaptation after too much training and too little recovery, with fatigue, performance decline and mood disturbance. It is hard to tell from non-functional overreaching and is a diagnosis of exclusion, which means other causes such as infection, organic disease, low energy intake, insufficient carbohydrate or protein, iron or magnesium deficiency and allergies must be ruled out first. Several markers are used, but none meets all criteria for general use. Methods, limits and funding Outcomes: Performance, fatigue, mood and hormone markers Limitations: A 2013 consensus; the abstract gives no numbers; many markers lack validation. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Mesas 2023 Is daytime napping an effective strategy to improve sport-related cognitive and physical performance and reduce fatigue? A systematic review and meta-analysis of randomised controlled trials. Br J Sports Med · PMID 36690376 · DOI	Systematic review meta analysis	291 22 randomised trials; 291 male participants (164 trained athletes, 127 active adults) aged 18 to 35	Daytime nap (12:30 to 16:50, most often 14:00) Best results with naps of 30 to under 60 minutes, and more than 1 hour between waking and the test Single naps in each trial · vs No nap	After a normal night of sleep, a nap improved cognitive and physical performance and reduced perceived fatigue. The benefits were also seen after partial sleep deprivation. They were larger for naps of 30 to under 60 minutes and when at least an hour passed between waking and the test. Standardised mean differences: cognitive 0.69; physical 0.99; fatigue -0.76 (Cognitive 0.37 to 1.00; physical 0.67 to 1.31; fatigue -1.24 to -0.28; I2 71.5% to 89.5%) Methods, limits and funding Outcomes: Cognitive performance, physical performance, perceived fatigue Limitations: Men only; mostly short laboratory tests; heterogeneity high; says nothing about how napping affects night sleep. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Milewski 2014 Chronic lack of sleep is associated with increased sports injuries in adolescent athletes. J Pediatr Orthop · PMID 25028798 · DOI	Observational survey with injury records	112 Adolescent student athletes, mean age 15 (range 12 to 18), at one school in the US	Average hours of sleep per night (self-reported) Under 8 hours versus 8 hours or more Retrospective injury records · vs Athletes sleeping 8 hours or more	Hours of sleep and school grade were the best predictors of injury. Athletes sleeping under 8 hours a night were 1.7 times as likely to have been injured as those sleeping 8 hours or more. Each higher school grade added about 1.4 times the odds. Odds ratio about 1.7 for under 8 hours (95% CI 1.0 to 3.0; P=0.04) Methods, limits and funding Outcomes: Injury recorded by the school athletic department Limitations: One school, 112 survey answers (70% of those invited), self-reported sleep, injuries reviewed after the fact: shows a link, not proof of cause. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Robey 2013 Effect of evening postexercise cold water immersion on subsequent sleep. Med Sci Sports Exerc · PMID 23377833 · DOI	Randomised crossover trial	11 Eleven trained male cyclists	Cold water immersion after evening exercise Not given in the abstract Single evening session (about 19:00), then a sleep study · vs Exercise alone, and no exercise	No differences in any whole-night sleep measure between exercise, exercise plus cold water immersion and no exercise. Body temperature changes were seen after immersion, but melatonin and recovery ratings were similar. Methods, limits and funding Outcomes: Sleep stages and timing by polysomnography; temperatures; melatonin; fatigue ratings Limitations: Eleven men, one night per condition, laboratory sleep study. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Silva 2021 Sleep extension in athletes: what we know so far - A systematic review. Sleep Med · PMID 33352457 · DOI	Systematic review	Athletes in 2 included studies (5 of 74 articles were eligible)	Sleep extension (time in bed or total sleep time extended by 26 to 106 minutes) Extra 26 to 106 minutes as studied Varied by study · vs Habitual sleep	The limited evidence suggests sleep extension may improve sports performance, with the size depending on what was measured. Six of fifteen measures showed a large effect; the rest ranged from trivial to medium. The authors call the conclusion tentative. 6 of 15 measures had a large effect size (Not given in the abstract) Methods, limits and funding Outcomes: Sports performance measures (15 measures in 2 studies) Limitations: Only 2 studies could be included. Risk of bias was high for the randomised trial and low for the non-randomised one; quality of evidence ranged from very low to moderate. Funding and conflicts: Research support from a non-US-government source is listed in the PubMed record; no conflict-of-interest statement in the record read. Read: abstract
Stutz 2019 Effects of Evening Exercise on Sleep in Healthy Participants: A Systematic Review and Meta-Analysis. Sports Med · PMID 30374942 · DOI	Systematic review meta analysis	23 studies of healthy adults after a single evening exercise session versus no exercise	One session of evening exercise Intensity and duration varied; moderators analysed Single session · vs No exercise	Compared with no exercise, evening exercise slightly lengthened the time to REM sleep (+7.7 minutes), increased slow-wave (deep) sleep by 1.3 percentage points and reduced light stage 1 sleep by 0.9 points. Sleep efficiency and total sleep time might be impaired after vigorous exercise ending one hour or less before bedtime. A higher body temperature at bedtime and harder exercise were linked to worse sleep, but those effects disappeared when one study was removed. The authors say the studies do not support the idea that evening exercise harms sleep. REM latency +7.7 min; slow-wave sleep +1.3 points; stage 1 -0.9 points (Not given in the abstract (p values 0.001 to 0.041)) Methods, limits and funding Outcomes: Sleep stages, sleep efficiency, wake after sleep onset, sleep onset latency Limitations: Healthy adults, one session at a time, not athletes in a hard training block; moderator results were fragile. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Trommelen 2023 Pre-sleep Protein Ingestion Increases Mitochondrial Protein Synthesis Rates During Overnight Recovery from Endurance Exercise: A Randomized Controlled Trial. Sports Med · PMID 36857005 · DOI	Randomised controlled trial	36 Thirty-six healthy young men after one evening endurance exercise session	Pre-sleep casein or whey protein 45 g, 30 minutes before sleep One night · vs Non-caloric placebo	Protein before sleep raised overnight muscle protein synthesis compared with placebo, and casein and whey did not differ. The trial measured muscle building in the laboratory, not sleep quality, performance or soreness. Mitochondrial 0.087 vs 0.067 %/h; myofibrillar 0.060 vs 0.047 %/h (protein vs placebo) (P = 0.005 and P = 0.012) Methods, limits and funding Outcomes: Overnight muscle protein synthesis rates (mitochondrial and myofibrillar) from muscle samples Limitations: One night, young men, an intravenous tracer method; muscle protein synthesis is a laboratory marker, not a proven gain in performance. Funding and conflicts: No funding or conflict-of-interest statement in the PubMed record read. Read: abstract
Walsh 2020 Sleep and the athlete: narrative review and 2021 expert consensus recommendations. Br J Sports Med · PMID 33144349 · DOI	Expert consensus narrative review	Athletes, mainly elite; review of sleep research plus an expert panel statement	Sleep inadequacy, sleep education and screening, napping and sleep extension (reviewed) Not given in the abstract	Elite athletes are prone to short sleep (under 7 hours) and poor sleep quality. Performance is reduced by a night or more without sleep; the effect of partial restriction over one to three nights is unclear. Athlete sleep studies often have weak experimental control, few females and questions about the sleep tools used. The panel advises an individual approach, not one number such as 7 to 9 hours for everyone, and says napping and sleep extension need more research. Methods, limits and funding Outcomes: Athlete sleep, performance, health; practitioner toolbox Limitations: Consensus and narrative review, not a pooled analysis; the abstract gives no numbers. Funding and conflicts: PubMed record lists a US NIH institute grant; no conflict statement in the record read. Read: abstract
s-fda-caffeine US FDA: Spilling the beans, how much caffeine is too much (content current as of 28 August 2024) · Source	Health agency n/a			Methods, limits and funding Read: full-text
s-nhlbi-sleep-apnea NHLBI: Sleep apnea, what is sleep apnea (last updated 9 January 2025) · Source	Health agency n/a			Methods, limits and funding Read: full-text
s-nhlbi-sleep-deficiency NHLBI: Sleep deprivation and deficiency (last updated 24 March 2022) · Source	Health agency n/a			Methods, limits and funding Read: full-text
s-nhs-insomnia NHS: Insomnia (page last reviewed 19 March 2024) · Source	Health agency n/a			Methods, limits and funding Read: full-text
s-nhs-sleep-apnoea NHS: Sleep apnoea (page last reviewed 11 May 2026) · Source	Health agency n/a			Methods, limits and funding Read: full-text

What we do not know yet

No trial read shows that extra sleep prevents sports injury; the injury evidence is observational and in teenagers.
The effect of losing a little sleep over one to three nights, the common real-world case, is unclear.
Almost all participants in the performance and nap studies were young men; women, older adults and casual exercisers are poorly covered.
No trial read tested tart cherry, magnesium or protein before bed for sleep in athletes.
No study read shows that wearing a sleep tracker, by itself, improves recovery or performance.
No source read says how common orthosomnia is.

How new research is added

New studies are found by a saved PubMed search and placed in a review queue before the page changes.

Lab markers

What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".

Other 4

●

Exercise performance tests

Lower after sleep loss; higher after sleep extension and naps in small studies in trials

Timed or measured tasks such as time to exhaustion, sprint speed, strength or skill scores, used to see whether sleep changes performance.

Moderate certainty

Results and what it means

Why it was measured

To see whether sleep loss, sleep extension or naps change how well people perform.

Statistical vs. clinical meaning

A laboratory test is not the same as winning a match or avoiding injury.

Safety implication

None reported in the abstracts.

Study	Result	People	Product
⁶	Average fall of 7.56% after sleep loss	69 publications, mostly men	Sleep loss
¹⁹	Physical performance improved after a daytime nap (SMD 0.99)	22 trials, 291 men	Daytime nap

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●

Sports or muscle-and-joint injury

Higher in adolescents who sleep less in trials

An injury recorded by a school, club or clinic during sport.

Low certainty

Results and what it means

Why it was measured

To see whether tired athletes get injured more.

Statistical vs. clinical meaning

A real outcome that matters, but the studies are observational.

Safety implication

Injured or very tired young athletes should be seen by a clinician.

Study	Result	People	Product
⁹	Odds ratio 1.58 for chronic poor sleep	7 studies of adolescents	Chronic lack of sleep
²⁰	1.7 times the odds with under 8 hours of sleep	112 adolescent athletes	Under 8 hours a night

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●

Total sleep time and sleep efficiency

Lower after late caffeine; mixed or small with tart cherry and magnesium in trials

How long a person actually sleeps in the night and the share of time in bed spent asleep, measured by sleep study, wrist sensor or diary.

Moderate certainty

Results and what it means

Why it was measured

To see whether late caffeine, a supplement or a habit changes how much sleep you get.

Statistical vs. clinical meaning

Sleep time is a main outcome of sleep, but long-term effects were not studied.

Safety implication

None reported in the abstracts.

Study	Result	People	Product
¹⁰	Caffeine reduced total sleep time by about 45 minutes	24 studies	Caffeine
¹³	Total sleep time and sleep efficiency higher with tart cherry juice	20 healthy adults	Tart cherry juice for 7 days

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●

Tracker agreement with polysomnography

High for sleep, low for wake, variable for sleep stages in trials

How closely a consumer device agrees with an in-lab sleep study, epoch by epoch (every 30 seconds).

Moderate certainty

Results and what it means

Why it was measured

To see whether tracker scores can be trusted.

Statistical vs. clinical meaning

A tracker score is an estimate, not a medical measurement.

Safety implication

A normal-looking tracker result cannot rule out a sleep disorder.

Study	Result	People	Product
⁵	Sensitivity 0.93 or higher, specificity 0.18 to 0.54	34 healthy young adults	Seven consumer devices
¹⁴	Stage-scoring score from 0.26 to 0.69	75 people	Eleven consumer devices

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Safety

What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.

Main points to know 4

Loud snoring with gasping or pauses, and heavy daytime sleepiness, need a doctor, not a tracker. Sleep apnea is when breathing stops and starts during sleep. The NHS lists loud snoring, gasping, snorting or choking noises, waking a lot, feeling very tired in the day, trouble concentrating and morning headaches. It says to see a GP if breathing stops and starts in sleep, if you make gasping or choking noises, or if you always feel very tired in the day. NHLBI says untreated sleep apnea raises the risk of stroke, heart attack and other serious problems. Diagnosis is by a sleep test, usually with devices worn overnight, not by a consumer tracker. Poor recovery that does not improve with more sleep may be a sign of a sleep disorder. Health agency guidance ^{30 27 5}
Do not drive or train when drowsy. NHLBI says sleepiness while driving, not related to alcohol, is responsible for serious car crash injuries and deaths. The NHS tells people with insomnia not to drive when they feel sleepy, and says that anyone with confirmed sleep apnoea and excessive sleepiness must not drive until the sleepiness is under control. After a night of little sleep, very hard training, night travel or a long drive home from an event, the sensible choice is to rest, not to push on. Health agency guidance ^{28 29 30}
Long-lasting tiredness or falling performance is not a reason to add supplements. A joint consensus statement describes overtraining syndrome as fatigue, falling performance and mood disturbance that lasts after too much training and too little recovery. It says other causes must be excluded first, including infection or other illness, not eating enough energy, too little carbohydrate or protein, iron or magnesium deficiency and allergies. Seeing a doctor is the first step, not a longer training block or a new product. No tracker score or blood marker meets all the criteria on its own. Consensus statement ¹⁸
No sleeping-pill advice is given here. This page does not recommend any sleeping pill or sleep aid. The NHS says doctors now rarely prescribe sleeping pills for insomnia because they can have serious side effects and you can become dependent on them, and that pharmacy sleep aids may help for 1 to 2 weeks at most and can make you drowsy. It also says sleeping pills can make sleep apnoea worse and should not be taken unless a doctor recommends them. Talk to a doctor or pharmacist about any sleep medicine. Health agency guidance ^{29 30}

Side effects 4

Effect	How often	Severity and recovery	Evidence
Less and lighter sleep after caffeine taken in the evening Caffeine in pre-workout products can be in the same range as a cup of coffee or more. The FDA lists insomnia or sleep disruption and anxiety among the signs of too much caffeine, and warns that pure or highly concentrated caffeine products can be toxic or even lethal.	Average about 45 minutes less sleep time and 7% lower sleep efficiency across 24 studies	Mild to moderate, depending on the person Not assessed	Systematic review ^{10 8}
Daytime drowsiness from pharmacy sleep aids The NHS says these products can make you drowsy and should not be used longer than 1 to 2 weeks. They are not recommended here.	Not given	Mild to moderate Not stated	Health agency guidance ²⁹
More worry about sleep after watching tracker data (orthosomnia) The authors suggest including trackers in cognitive behavioural therapy for insomnia.	Not known; only case reports	Varies Not assessed	Case reports ²
Very little sleep, then hard exercise: lower performance and, in teenagers, more injuries These are risks of too little sleep, not harms of a treatment.	Average 7.56% lower performance after sleep loss; 1.58 times the odds of injury for chronic poor sleep in adolescents	Varies Not assessed	Systematic reviews ^{6 9}

Medicines and supplements 4

With	Why it matters	Importance	Evidence	What to do
Caffeine and some medicines drug		The FDA says some conditions and some medications can make people more sensitive to caffeine.	Health agency guidance Low certainty ²⁶	Ask a pharmacist whether your medicines change how caffeine affects you, especially before using pre-workout products.
Alcohol, antihistamine sleep aids and other sedating products general	Could add to drowsiness	Not studied in the sources read for this page.	Absence of evidence Not enough evidence ²⁹	The NHS notes pharmacy sleep aids with an antihistamine can cause drowsiness. Mixing sedating products is a reasonable thing to raise with a pharmacist. (General safety guidance, not from a source read.)
Sleeping pills and sleep apnoea condition		The NHS says sleeping pills can make sleep apnoea worse.	Health agency guidance Low certainty ³⁰	If you snore loudly or gasp in sleep, see a doctor before using any sleep aid.
Magnesium supplements and medicines or kidney disease supplement	Not studied in the sources read	No interaction data were read for the magnesium trials.	Absence of evidence Not enough evidence ¹⁷	Ask a doctor or pharmacist before taking magnesium if you take regular medicines or have kidney problems. (General safety guidance, not from a source read.)

Who should check first 7

Situation	Advice	Evidence
Loud snoring, gasping or pauses in breathing at night, or heavy daytime sleepiness	See a doctor for a sleep test before relying on sleep tips, supplements or a tracker. Do not use sleeping pills unless a doctor recommends them.	Health agency guidance ^{30 27}
Pregnancy and breastfeeding	The FDA recommends talking to a health care provider about whether you need to limit caffeine if you are pregnant, trying to become pregnant or breastfeeding. No source read covers the other options on this page in pregnancy.	Health agency guidance ²⁶
Children and teenagers	The FDA says too much caffeine in children and teens can cause a faster heart rate, palpitations, anxiety and sleep problems, and that medical experts advise against energy drinks for them. Teenage athletes who sleep little or get hurt often should talk to a clinician.	Health agency guidance ^{26 9}
Heart conditions, high blood pressure or being sensitive to caffeine	Pre-workout products and energy drinks can contain a lot of caffeine. Ask a clinician before using them. (General safety guidance, not from a source read.)	General safety guidance
Kidney disease	Ask a doctor before using extra protein, protein before bed or magnesium supplements. (General safety guidance, not from a source read.)	General safety guidance
Heart disease or other long-term conditions and cold water immersion	Cold exposure carries its own risks; see our cold and heat exposure page and ask a clinician first. Do not do it alone in open water. (General safety guidance, not from a source read.)	General safety guidance
Taking prescription medicines	Show a doctor or pharmacist every supplement before you start. Do not stop or change a prescribed medicine because of something read on a recovery page. (General safety guidance, not from a source read.)	General safety guidance

Overdose, product quality and regulators

Body	Action	Date
NHS (UK) (United Kingdom)	Describes sleep apnoea symptoms and says to see a GP; says sleeping pills can make it worse; says people with confirmed sleep apnoea and excessive sleepiness must not drive until symptoms are controlled and may need to tell the DVLA. source	2026-05-11
National Heart, Lung, and Blood Institute (NIH) (United States)	Says untreated sleep apnea raises the risk of stroke, heart attack and other problems and that diagnosis is by a sleep study. source	2025-01-09
NHS (UK) (United Kingdom)	Says to see a GP if sleep changes have not helped or trouble sleeping has lasted months; says CBT may be offered, sleeping pills are rarely prescribed and pharmacy sleep aids should not be used longer than 1 to 2 weeks; advises not to drive when sleepy. source	2024-03-19
National Heart, Lung, and Blood Institute (NIH) (United States)	Says sleep deficiency is linked with a higher chance of injury and that sleepiness while driving causes serious crash injuries and deaths. source	2022-03-24
US Food and Drug Administration (United States)	Cites 400 mg of caffeine a day as an amount not generally associated with negative effects for most adults, notes wide differences in sensitivity, advises talking to a provider if pregnant or breastfeeding, and advises against energy drinks for children and teens. source	2024-08-28

When to get medical help

Chest pain, fainting, a very fast or uneven heartbeat or trouble breathing during or after exercise or after a caffeine product: call emergency services (999 in the UK, 911 in the US). General safety guidance, not from a source read.
Falling asleep at the wheel or nearly crashing because of tiredness: stop in a safe place and do not drive until you have slept. See a doctor about the sleepiness. The NHS and NHLBI both warn about driving when sleepy.
Loud snoring with gasping, choking or pauses in breathing, or always feeling very tired in the day: see a doctor soon (NHS).
Tiredness, low mood or falling performance that lasts for weeks despite rest, or thoughts of harming yourself: see a doctor. If you are in danger or thinking of suicide, contact your local emergency number or crisis service (they differ by country, so none are listed here).

Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.

General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.

Frequently asked questions

How much sleep do athletes need?

There is no single answer. A 2020 expert consensus says one number for everyone, such as 7 to 9 hours, is unlikely to be ideal and recommends an individual approach based on the athlete's own needs. It also notes that elite athletes often sleep under 7 hours.

²⁵

Does sleep help recovery from exercise?

Too little sleep lowers performance in pooled studies, and two reviews found that sleeping longer or napping was the most helpful sleep strategy for later performance. The studies are small and mostly in young men, so the size of the benefit for you is not known.

^{6 7}

Does napping help recovery and performance?

A 2023 review of 22 trials found that naps of 30 to under 60 minutes taken in the afternoon improved physical and thinking tests and reduced tiredness in young men. Results varied a lot, women and older adults were not studied, and the review did not look at night sleep.

¹⁹

Does sleep extension work?

It is promising but thin. A review of two studies called its conclusion tentative, a larger review found extension among the most effective strategies, and a trial of 12 men found a longer hold time after six nights of extra time in bed, mainly because it felt easier.

^{22 7 1}

Does missing sleep raise the chance of injury?

In studies of teenage athletes, those who slept less were more likely to be injured (about 1.7 times the odds under 8 hours in one school; 1.58 times in a review). These are links, not proof, and no trial of extra sleep and injury was read.

^{20 9}

Is it bad to work out late in the evening?

A review of 23 studies found a single evening workout did not harm sleep on average. Very hard exercise ending within about an hour of bedtime might make sleep worse. The NHS advises people with insomnia not to exercise for at least 4 hours before bed.

^{23 29}

Do tart cherry juice, magnesium or protein before bed improve sleep or recovery?

The evidence is thin. Two very small trials linked tart cherry juice with longer sleep, three small trials in older adults with insomnia found magnesium shortened time to fall asleep by about 17 minutes, and protein before bed raised a muscle-building marker in one trial that did not measure sleep or performance. Ask a doctor or pharmacist before using supplements.

^{13 16 17 24}

Does cold water immersion improve sleep after exercise?

Results were mixed. Eleven cyclists had no change in sleep, 12 runners had more deep sleep early in the night after whole-body immersion, and a 2023 review found no effect, based on few studies. Cold exposure has its own risks.

^{21 4 7}

When should I stop caffeine before bed?

A 2023 review estimated that coffee should be finished at least 8.8 hours before bed, and a pre-workout serve at least 13.2 hours before, to avoid losing sleep time. A trial found 400 mg disrupted sleep even 6 hours before bed. People vary, so these are averages, not advice.

^{10 8}

How accurate are sleep trackers compared with a sleep study?

They detect sleep well but are weaker at detecting wake, and only fair at sleep stages. In one study sensitivity was 0.93 or higher but specificity for wake was 0.18 to 0.54, and a 2025 review found significant differences in sleep time, efficiency and time awake compared with polysomnography.

^{5 15 14}

Can my watch or ring tell me that I have recovered, and what is orthosomnia?

Whether a tracker tells you that you have recovered is not established. Orthosomnia is worry about sleep caused by tracker data; it has been described in case reports, so how common it is remains unknown. If checking a tracker makes sleep or training worse, take a break and ask a doctor.

What are the signs of overtraining, and when should I see a doctor?

A joint consensus describes long-lasting fatigue, falling performance and mood disturbance. See a doctor if tiredness or low mood lasts for weeks despite rest, or if you snore loudly with gasping, or feel very sleepy in the day. Do not drive when drowsy.

^{18 30}

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Editorial transparency

Written by: AlternativeMed editorial team. Research compiled with AI assistance, then checked against PubMed records.
Medical review: None. This page has not been reviewed by a physician or pharmacist.
First published: 2026-10-31
Last substantive update: 2026-10-31
How we research: We searched PubMed, re-read the abstract of every review, trial and consensus statement cited, and read the NHS, NHLBI and FDA pages in full. Full texts of the papers were not read. Certainty ratings are the compiler's own reading. Funding is not stated in most abstracts, and this is noted where relevant.
How we rate evidence: See "How we rate evidence" in the Evidence tab.
Independence: No product is promoted on this page. No affiliate links are shown.

Sources 30

Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.

Arnal PJ, Lapole T, Erblang M, Guillard M, Bourrilhon C, Léger D, Chennaoui M, Millet GY. Sleep Extension before Sleep Loss: Effects on Performance and Neuromuscular Function.. Med Sci Sports Exerc. 2016. PMID 27015382. DOI 10.1249/MSS.0000000000000925. (abstract)
Baron KG, Abbott S, Jao N, Manalo N, Mullen R. Orthosomnia: Are Some Patients Taking the Quantified Self Too Far?. J Clin Sleep Med. 2017. PMID 27855740. DOI 10.5664/jcsm.6472. (abstract)
Bonnar D, Bartel K, Kakoschke N, Lang C. Sleep Interventions Designed to Improve Athletic Performance and Recovery: A Systematic Review of Current Approaches.. Sports Med. 2018. PMID 29352373. DOI 10.1007/s40279-017-0832-x. (abstract)
Chauvineau M, Pasquier F, Guyot V, Aloulou A, Nedelec M. Effect of the Depth of Cold Water Immersion on Sleep Architecture and Recovery Among Well-Trained Male Endurance Runners.. Front Sports Act Living. 2021. PMID 33870188. DOI 10.3389/fspor.2021.659990. (abstract)
Chinoy ED, Cuellar JA, Huwa KE, Jameson JT, Watson CH, Bessman SC, Hirsch DA, Cooper AD, Drummond SPA, Markwald RR. Performance of seven consumer sleep-tracking devices compared with polysomnography.. Sleep. 2021. PMID 33378539. DOI 10.1093/sleep/zsaa291. (abstract)
Craven J, McCartney D, Desbrow B, Sabapathy S, Bellinger P, Roberts L, Irwin C. Effects of Acute Sleep Loss on Physical Performance: A Systematic and Meta-Analytical Review.. Sports Med. 2022. PMID 35708888. DOI 10.1007/s40279-022-01706-y. (abstract)
Cunha LA, Costa JA, Marques EA, Brito J, Lastella M, Figueiredo P. The Impact of Sleep Interventions on Athletic Performance: A Systematic Review.. Sports Med Open. 2023. PMID 37462808. DOI 10.1186/s40798-023-00599-z. (abstract)
Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed.. J Clin Sleep Med. 2013. PMID 24235903. DOI 10.5664/jcsm.3170. (abstract)
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