In 30 seconds
- A single night without sleep reduced muscle protein synthesis by 18% the next day, with 21% more cortisol and 24% less testosterone.
- Five nights of 4 hours in bed lowered muscle protein synthesis by 19%. With three interval sessions, it was maintained.
- A week of sleeping less than 5 hours lowered testosterone by 10-15% in young men.
- Deep sleep, linked to growth hormone, fell from 18.9% of the night between the ages of 16 and 25 to 3.4% between 36 and 50.
While you sleep, your muscles keep working. Sleeping little or not at all slows muscle protein synthesis, raises cortisol, lowers testosterone and makes you perform worse the next day. This is what has been measured, with the figures and the nuances.
What happens in your muscles while you sleep
Deep sleep is the time for growth hormone: its release is linked to that phase 8. In 149 healthy men, the amount of growth hormone was associated with deep sleep, regardless of age 4.
And the body asks for it after hard work. In six marathon runners, total sleep time rose over the 4 nights after the race, and deep sleep over the first two 8.
The night is also a long fast. What you eat before bed counts, and we look at it in protein before bed.
Level of evidence by outcome
| Outcome | Evidence | What the data show |
|---|---|---|
| Less muscle protein synthesis with short sleep | Moderate | 18-19% less after a sleepless night or five nights of 4 hours, in two trials. |
| Higher cortisol and lower testosterone | Moderate | Changes of 10 to 24% in several small trials. |
| Performance the next day | High | 7.56% lower on average in 77 studies; maximal strength is the least affected. |
| Growth hormone and deep sleep | Moderate | Its release is linked to deep sleep, which falls sharply in middle age. |
| Recovery of strength after muscle damage | No clear effect | 48 hours without sleep did not delay the recovery of strength in one trial. |
| Training to compensate | Preliminary | Interval training maintained protein synthesis with 4 hours of sleep in one trial. |
The rating is our own, based on the number of studies, their quality and the consistency of the results.
The key studies
| Study | Type | Sample | Outcome |
|---|---|---|---|
| Lamon et al., 2021 | Crossover trial | 13 young adults (7 men and 6 women) | One night without sleep: 18% less muscle protein synthesis, 21% more cortisol and 24% less testosterone. 1 |
| Saner et al., 2020 | Trial | 24 young men | Five nights of 4 hours in bed: myofibrillar protein synthesis of 1.24% a day, compared with 1.53% with 8 hours and 1.61% with 4 hours plus intervals. 2 |
| Leproult and Van Cauter, 2011 | Laboratory study | 10 men aged about 24 | Eight nights sleeping less than 5 hours: testosterone 10-15% lower, especially between 14:00 and 22:00. 3 |
| Van Cauter et al., 2000 | Analysis of sleep studies | 149 men aged 16 to 83 | Growth hormone was associated with deep sleep, which fell from 18.9% of the night to 3.4% between youth and middle age. 4 |
| Dáttilo et al., 2020 | Crossover trial | 10 men | 48 hours without sleep after 240 eccentric contractions: strength recovered in the same way, but IL-6 and cortisol rose. 5 |
| Craven et al., 2022 | Meta-analysis | 77 studies | Short sleep lowered performance by 7.56%: maximal strength by 2.85% and strength endurance by 9.85%. 6 |
One night without sleep
What changed the next day
One sleepless night
In a trial with 13 young adults, 7 men and 6 women, each person spent one night without sleep and another sleeping normally. The day after the sleepless night, muscle protein synthesis after eating was 18% lower 1.
The hormonal environment also changed: cortisol rose by 21% and testosterone fell by 24%. The markers of muscle breakdown did not change 1.
The authors conclude that a single night is enough to create anabolic resistance, that is, a muscle that responds less to food, and an environment that favours catabolism 1.
Several short nights
This is the closest thing to a bad week at work. In one trial, 24 young men spent five nights in one of three groups: 8 hours in bed, 4 hours, or 4 hours with three high-intensity interval sessions 2.
- 8 hours: myofibrillar protein synthesis, that of the fibres that contract, was 1.53% a day.
- 4 hours: it fell to 1.24%, around 19% less.
- 4 hours with intervals: it stayed at 1.61% 2.
Training does not replace sleep, but in that trial it maintained protein synthesis despite short sleep 2. A good reason to keep training during a week of short nights.
Testosterone feels it too. In 10 men aged about 24, eight nights of sleeping less than 5 hours lowered it by 10-15%, especially between 14:00 and 22:00. That is the drop that corresponds to ageing 10 to 15 years, since it falls by 1-2% a year with age 3.
And the recovery of strength?
There is a nuance here. In one trial, 10 men did 240 eccentric contractions of the quadriceps, an effort designed to damage the muscle. They then spent 48 hours without sleep or three normal nights 5.
Strength and creatine kinase, a marker of muscle damage, followed the same course in both cases. What changed was the environment: without sleep, IL-6, a signal of inflammation, and cortisol rose 5.
In other words: in that study, short sleep did not delay the recovery of strength, but it did alter hormones and inflammation. More studies are needed to know what happens with weeks of short sleep.
77 studies
How much performance fell after short sleep
Performance does suffer
Where there is no doubt is performance. In 77 studies, short sleep lowered next-day performance by 7.56% on average 6. This is how it affected what you train most:
- Maximal strength: 2.85% lower, the capacity that suffers least.
- Strength endurance: 9.85% lower.
- Anaerobic power: 6.26% lower.
- Skill and accuracy: 20.9% lower 6.
And each hour awake before training took away around 0.4% 6. You will find all the data in sleep deprivation and performance.
From 35: less deep sleep
This figure matters if you are over 35. In 149 men, deep sleep fell from 18.9% of the night between the ages of 16 and 25 to 3.4% between 36 and 50 4.
At the same time, growth hormone secretion fell by 372 µg per decade between youth and middle age, and then kept falling, more slowly 4. With less deep sleep as standard, looking after the amount and regularity of your sleep counts even more.
Hours of sleep
Aim for 7-9 hours and adjust it to you
How much to sleep to recover
The expert consensus on sleep in athletes notes that many usually sleep less than 7 hours, with awakenings. It considers that a single figure, such as 7-9 hours, is not ideal for everyone, and recommends tailoring it to each person 7.
- Aim for 7-9 hours and adjust according to how you recover. Our sleep test helps you see your ideal number of hours 7.
- Keep training during a week of short nights. In the trial with five short nights, interval training maintained protein synthesis 2.
- Watch what takes away deep and REM sleep, such as alcohol with dinner: we look at it in alcohol and sleep.
- Use naps when the night falls short. We explain how long and when in napping and performance.
If you sleep poorly on an ongoing basis, talk to your doctor.
Frequently asked questions
Do your muscles recover while you sleep?
Sleep is part of recovery. In one trial, a night without sleep lowered muscle protein synthesis by 18% the next day, and in another, five nights of 4 hours lowered it by 19%.
Does lack of sleep make you lose muscle?
What has been measured is that it slows muscle protein synthesis and creates a less favourable hormonal environment, with more cortisol and less testosterone. The authors see this as a step towards losing muscle mass if the lack of sleep continues.
How many hours of sleep do you need to recover from training?
The general reference is 7 to 9 hours, but the expert consensus on sleep in athletes recommends tailoring it to each person, according to how they feel and recover.
Is it true that growth hormone is released during sleep?
Yes, especially during deep sleep. In 149 men, its release was associated with the amount of deep sleep, which falls sharply between the ages of 25 and 50.
Sources
- Lamon S, Morabito A, Arentson-Lantz E, Knowles O, Vincent G, Condo D, Alexander SE, Garnham A, Paddon-Jones D, Aisbett B. The effect of acute sleep deprivation on skeletal muscle protein synthesis and the hormonal environment. Physiol Rep. 2021;9(1):e14660. View publication
- Saner N, Lee M, Pitchford N, Kuang J, Roach GD, Garnham A, Stokes T, Phillips S, Bishop D, Bartlett JD. The effect of sleep restriction, with or without high-intensity interval exercise, on myofibrillar protein synthesis in healthy young men. J Physiol. 2020;598(8):1523-1536. View publication
- Leproult R, Van Cauter E. Effect of 1 week of sleep restriction on testosterone levels in young healthy men. JAMA. 2011;305(21):2173-2174. View publication
- Van Cauter E, Leproult R, Plat L. Age-related changes in slow wave sleep and REM sleep and relationship with growth hormone and cortisol levels in healthy men. JAMA. 2000;284(7):861-868. View publication
- Dáttilo M, Antunes HKM, Galbes NMN, Mônico-Neto M, Souza HDS, Quaresma MVLDS, Lee KS, Ugrinowitsch C, Tufik S, Mello MT. Effects of sleep deprivation on acute skeletal muscle recovery after exercise. Med Sci Sports Exerc. 2020;52(2):507-514. View publication
- 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;52(11):2669-2690. View publication
- Walsh NP, Halson SL, Sargent C, et al. Sleep and the athlete: narrative review and 2021 expert consensus recommendations. Br J Sports Med. 2021;55(7):356-368. View publication
- Halson SL. Sleep in elite athletes and nutritional interventions to enhance sleep. Sports Med. 2014;44(Suppl 1):S13-S23. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
