When it comes to fitness, this slow-wave sleep is the most important of the night as this is when growth hormone is released by the pituitary gland at the base of the brain. Studies reveal that when sleep is restricted GH release is reduced. Without adequate levels of GH, recovery from workouts takes longer and fitness building requires more time than would otherwise be necessary. As a result, the sleep-deprived athlete responds poorly to training both in the short term and over the course of a season. On the other hand, training volume has been shown to have an effect on sleep patterns.
Adequate sleep is a necessity for the serious athlete.
It must be a major consideration every day, especially during heavy training and when peaking for important races. Establishing sleep habits that put you in bed at a standard time every night and allow for eight hours or more of sleep will do as much to peak your fitness as will difficult workouts. Mougin, F., et al. 1991. Effects of sleep disturbances on subsequent physical performance. Taylor, S.R., et al. 1997.