The benefits of good sleep come into particular focus for athletes. Post-exercise recovery with extra sleep accelerates the building of muscle, strength, and endurance.
Research shows that athletic performance improves with sufficient sleep. Rested athletes are faster, more accurate, and have a quicker reaction time. Mild sleep deprivation does not negatively affect aerobic capacity, but it does affect reaction time.
The Stanford Sleep Disorders Clinic and Research Laboratory has attempted to quantify the effect of sleep on athletic performance. A study of swimmers asked to sleep 10 hours a day for six to seven weeks found notable improvements. This involved forcing the athletes to sleep longer than most people do to see if extra sleep in athletes undergoing heavy training had a benefit. Swim times were faster, and reaction times and turn times in the water improved. Kick stroke count increased as well.
A similar regimen (10 hours of sleep per day during heavy training) for football players also produced improvements. Sprint times declined and mood as measured by the POMS (Profile of Mood States) test (an indicator of physiological stress) increased. In addition to the swimming and football athletes Stanford has studied athletes from basketball, track and field, tennis, golf, and cross country. The evidence, usually based on small sample sizes, suggests more sleep results in improved physical performance.
Researchers have conjectured that long, heavy sleep impacts athletic performance due to the fact that growth hormones are released during deep sleep and the extra sleep encourages more hormone production.
Trainers recognize the benefits of sufficient and even long sleep for athletes in heavy training. Short sleep is likewise detrimental. Cutting two hours from the normal sleep time degrades athletic performance roughly the same as drinking enough to produce a blood alcohol level of 0.05. Competitive athletes often have sleep onset insomnia before an important event, due to nervousness.
Some top-level athletes attempt to cheat by taking supplements of human growth hormone. Natural increase of HGH can be promoted by both exercise and sleep. Physiologists speak of exercise-induced growth hormone response, which resistance training is known to cause. The load and frequency of the resistance influence the amount of hormone released.
Does exercise make you sleep better? There is evidence that growth hormone (GH)-releasing hormone stimulates NREM sleep. Very heavy exercise experienced by world-class athletes shifts the sleep architecture. The REM latency – which is to say the time period after the person goes to sleep before REM starts – is longer, and the sleeper has less REM during the first half of the night than normally.
The stress hormone cortisol seems to promote REM sleep and exercise reduces cortisol levels.
The English Institute of Sport measured sleep parameters of some athletes at the 2012 London Olympics and found slightly worse sleep efficiency and fragmentation index than non-athletes in the same age range, although the difference was not dramatic and on the whole the athletes had numbers in the normal range.
Muslim athletes who fast during daylight hours during Ramadan are known to take a performance hit. It is not clear whether the change in eating patterns affect sleep duration, time, and quantity enough to make a difference in athletic performance.
Women endurance athletes are known to have menstrual irregularities, but we do not know of any attempt to explicitly work out the relationship among intense training, sleep patterns, and menstruation.
One way endurance athletes train involved sleeping in low air pressure environments to encourage the formation of red blood cells. The bed is inside a tent that simulates the atmosphere in the mountains. Altitude insomnia is known to affect people who travel to the mountains and there has been concern among sports medicine people that this practice may lower sleep efficiency so much as to outweigh any blood-building benefits. A study by Sports Medicine Australia found that although the effect on sleep was measurable, it varied greatly from person to person and was not great enough to cause the practice to be halted.