The restoration theory of sleep suggests that during the day, wear and tear on our bodily tissues and organs leads to damage, then at night during sleep, the body repairs these damaged tissues and cells (Adam & Oswald, 1983). Evidence from empirical research, however, suggests that only non-REM sleep is involved in restoring the body. According to Hartmann (1973), there is an increase in the amount of time devoted to nREM sleep following periods of intense exercise and this has been demonstrated in several species of animal.

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Functions of Sleep: Ongoing Study Continues to Show That Extra Sleep Improves Athletic Performance A new peice of research has provided evidence that may help psychologists understand the functions of sleep.