Sleep and muscle growth

Muscles grow not during training but during recovery, and the most important part of that recovery falls at night. The editorial team examined which physiological processes during sleep support hypertrophy, what happens to protein synthesis and hormones with sleep deprivation, and which simple steps really help.

Why sleep is part of the training process

Strength training is a stimulus, and hypertrophy is the adaptive response to it. Between these two events a series of processes takes place: repair of damaged structures, synthesis of new contractile proteins, replenishment of glycogen stores, and ‘remodelling’ of the neuromuscular system. A significant part of these processes is most active precisely when the body is at rest, that is, during sleep.

Sleep is not uniform. Over the course of the night a person goes through 4–6 cycles, in each of which light sleep, deep slow-wave sleep and the rapid eye movement (REM) phase alternate. In the first half of the night deep sleep predominates, in the second — REM. Deep sleep is especially important for physical recovery, and REM for learning motor skills and emotional regulation.

The hypothesis about the role of sleep in muscle recovery was formulated in a review by Dattilo and co-authors (2011): the authors noted that sleep deprivation creates a catabolic hormonal environment — lower levels of anabolic hormones and higher cortisol — and thereby can slow recovery after exercise. Subsequent experimental studies have largely confirmed this logic.

It is important to understand the scale: sleep does not ‘build’ muscle by itself, without a training stimulus and sufficient protein. But its chronic deficit can noticeably reduce the return from even a perfectly designed programme. That is why we regard sleep as the third element of the triad, together with training load and nutrition.

The hormonal night: somatotropin, testosterone, cortisol

The largest release of growth hormone over the day in healthy adult men falls during the first episode of deep slow-wave sleep, shortly after falling asleep. This link was described by Van Cauter and colleagues: suppression of deep sleep is accompanied by a decrease in nocturnal somatotropin secretion. Growth hormone stimulates lipolysis and the synthesis of insulin-like growth factor-1 (IGF-1), although its direct contribution to hypertrophy in adults is often overestimated.

Testosterone in men has a circadian rhythm with a maximum in the morning, and its nocturnal rise depends on sleep. In a small study by Leproult and Van Cauter (2011), restricting sleep to 5 hours a night for a week lowered daytime testosterone levels in young healthy men by 10–15% — comparable to the effect of ageing by several years.

Cortisol, on the contrary, shifts with sleep deprivation: its evening level remains higher than usual. Cortisol is a catabolic hormone that promotes the breakdown of proteins and, with chronic elevation, hinders recovery. The combination of lower testosterone and higher cortisol is what creates the ‘catabolic environment’ that Dattilo and co-authors wrote about.

At the same time hormones should not be overestimated. Fluctuations within the physiological norm have a moderate effect on hypertrophy compared with training volume and protein intake. The problem of sleep deprivation lies rather in the totality of effects — hormonal, metabolic and behavioural.

Muscle protein synthesis and sleep deprivation

Direct evidence of the link between sleep and muscle anabolism was obtained by Lamon and co-authors (2021). After a single night of total sleep deprivation, postabsorptive muscle protein synthesis in young people fell by about 18% compared with normal sleep, plasma cortisol rose and testosterone fell. This was a one-off intervention, but it shows how quickly metabolism responds.

Sleep deprivation also worsens insulin sensitivity, and hence the uptake of nutrients by muscles. A few nights of shortened sleep are enough for signs of insulin resistance to appear in healthy people. For an athlete this means worse glycogen recovery and less efficient use of carbohydrates after training.

An indirect route is the quality of training itself. A review by Knowles and co-authors (2018) showed that insufficient sleep more often impairs the performance of high-repetition strength exercises and submaximal loads than a one-rep maximum. Fewer quality sets means a weaker stimulus for growth, even if recovery afterwards proceeds normally.

Finally, sleep deprivation affects behaviour: appetite for high-calorie food increases, motivation decreases, and missed training sessions become more frequent. All of this imperceptibly ‘eats up’ progress over weeks and months.

• Direct effects:lower muscle protein synthesis, a shift in the balance of testosterone and cortisol.
• Metabolic effects:worsening of insulin sensitivity and glycogen recovery.
• Training effects:a smaller working volume, worse technique, a higher subjective level of effort.

Sleep during a calorie deficit: muscle or fat

For those who are ‘cutting’, the study by Nedeltcheva and co-authors (2010) is especially telling. Participants kept the same calorie deficit for two weeks, but in one phase they slept 8.5 hours and in the other 5.5 hours. Body weight decreased by roughly the same amount, yet the composition of the lost weight differed dramatically.

With short sleep the proportion of fat lost decreased by about 55%, while the loss of fat-free mass increased by about 60% compared with full sleep. In other words, on the same diet, sleep deprivation forced the body to ‘burn’ more muscle tissue and preserve fat. Participants also reported a stronger feeling of hunger.

The study was small and lasted only two weeks, and the participants did not perform strength training. Nevertheless it illustrates the principle well: during a deficit, when anabolic signals are already weakened, sleep becomes one of the main protectors of muscle mass.

The practical takeaway for athletes and bodybuilders preparing for competition: cutting sleep for the sake of extra cardio or work is a bad bargain. It is better to fall a few hundred kilocalories short on expenditure than to lose muscle.

What can be done in practice

First and most important is duration. Most adult athletes need at least 7–9 hours of sleep, and during periods of high loads — more. A stable time of going to bed and getting up, including at weekends, helps to synchronise circadian rhythms and deepen sleep.

Second is protein before bed. A study by Res and co-authors (2012) showed that 40 g of casein taken before sleep after an evening workout increased nocturnal muscle protein synthesis. In a 12-week study by Snijders and co-authors (2015), a protein supplement before bed combined with strength training was accompanied by greater gains in muscle mass and strength than placebo. Importantly, in these works the protein also increased total daily intake.

Third is sleep hygiene: a cool (about 18–20 °C), dark and quiet bedroom, limiting bright screen light an hour before sleep, and avoiding caffeine in the second half of the day. For those who train late in the evening it is useful to give yourself time to ‘cool down’ — a warm shower and a calm routine speed up falling asleep.

Fourth — do not try to compensate for chronic sleep deprivation with supplements. Melatonin can help with a change of time zones, but it does not remove the causes of poor sleep. If sleep problems are persistent — snoring, awakenings, daytime sleepiness — it is worth seeing a doctor: sleep apnoea occurs in athletes too, especially in strength sports with a large body mass.

Editorial conclusions

Sleep is directly linked to muscle growth: the main release of growth hormone occurs during deep sleep, night sleep maintains testosterone levels, and its deprivation reduces muscle protein synthesis after just one night.

During a calorie deficit, sleep deprivation forces the body to lose more muscle mass and less fat, so during ‘cutting’ periods sleep becomes even more important.

The most effective steps are simple and free: 7–9 hours of sleep, a stable schedule, protein in the evening and comfortable conditions in the bedroom.

We also advise reading our materials on how much an athlete should sleep, on daytime sleep for recovery, and on casein protein before bed.

References

1. Dattilo M, Antunes HKM, Medeiros A, et al. Sleep and muscle recovery: endocrinological and molecular basis for a new and promising hypothesis. Med Hypotheses. 2011;77(2):220–222.
2. Lamon S, Morabito A, Arentson-Lantz E, et al. The effect of acute sleep deprivation on skeletal muscle protein synthesis and the hormonal environment. Physiol Rep. 2021;9(1):e14660.
3. 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.
4. Nedeltcheva AV, Kilkus JM, Imperial J, Schoeller DA, Penev PD. Insufficient sleep undermines dietary efforts to reduce adiposity. Ann Intern Med. 2010;153(7):435–441.
5. Res PT, Groen B, Pennings B, et al. Protein ingestion before sleep improves postexercise overnight recovery. Med Sci Sports Exerc. 2012;44(8):1560–1569.
6. Snijders T, Res PT, Smeets JSJ, et al. Protein ingestion before sleep increases muscle mass and strength gains during prolonged resistance-type exercise training in healthy young men. J Nutr. 2015;145(6):1178–1184.
7. Van Cauter E, Plat L. Physiology of growth hormone secretion during sleep. J Pediatr. 1996;128(5 Pt 2):S32–S37.
8. Knowles OE, Drinkwater EJ, Urwin CS, Lamon S, Aisbett B. Inadequate sleep and muscle strength: implications for resistance training. J Sci Med Sport. 2018;21(9):959–968.