What happens during sleep
Most of the growth hormone (GH) is released during deep sleep (slow waves), especially in the first half of the night. GH stimulates protein synthesis, fat mobilization and tissue regeneration. Cortisol falls during sleep, allowing the anabolic process to dominate.
Sleep deprivation and performance
Mah et al. (2011) showed that extending sleep from 8 to 10 h improves sprint performance, reaction time and mood. VanHelder and Radomski (1989) quantified it: 30 hours without sleep reduce VO2max by 3% and muscle strength by up to 5%.
Leproult & Van Cauter, "Effect of 1 Week of Sleep Restriction on Testosterone Levels in Young Healthy Men", JAMA, 2011
Sleep and muscle recovery
A study with elite collegiate athletes found that those sleeping below 8 h were 1.7× more likely to get injured over the season. The muscle repair cycle peaks between midnight and 3 a.m.
Practical strategies
Avoiding screens 60 to 90 minutes before bed reduces the suppression of melatonin by blue light. Bedroom temperature between 18 and 20°C. A consistent schedule routine: the circadian rhythm anchors to a fixed wake-up time. For night training: casein or Greek yogurt before sleep keeps muscle synthesis going during the night.
The landmark study on sleep and sport came from Stanford. Cheri Mah followed 11 players on the university basketball team who spent 5 to 7 weeks aiming to stay at least 10 hours in bed per night. Total sleep time rose by an average of 111 minutes and the effect on the court was objective: the 282-foot sprint dropped from 16.2 to 15.5 seconds, free throw accuracy rose 9% and 3-point accuracy 9.2%. No change in training, just more sleep (Mah et al., 2011).
The link between short sleep and injury has also been quantified. Milewski and colleagues followed 112 adolescent athletes through the season and found that sleeping less than 8 hours per night was associated with 1.7 times more risk of musculoskeletal injury compared with those who slept 8 hours or more. In that work, hours of sleep per night were one of the best independent predictors of injury (Milewski et al., 2014).
Endocrine recovery explains much of the phenomenon. About 70% of growth hormone pulses during sleep coincide with slow-wave sleep, concentrated in the pulse that occurs right after falling asleep (Van Cauter, 1996). That is why elite athletes protect sleep volume as part of training: Federer aims at 11 to 12 hours a day adding night and nap, LeBron James puts sleep as his number one recovery tool and Usain Bolt slept 8 to 10 hours per night during his career.
