The restoration theory of sleep function is carried out by Oswald, who argues that the purpose of sleep is to restore depleted energy reserves, eliminate waste products from muscles, repair cells and recover physical abilities that have been lost during the day.
Evidence for this theory is firstly by Shapiro, who found that people who ran an ultra marathon slept 1.5 hours longer then they did two nights following the race. In addition, stage four occupied a much greater proportion of the total sleep time and the proportion of REM sleep decreased. …
