Fig. 3.  Low aerobic capacity runners (LCR) spent more time awake and less time in nonrapid eye movement (NREM) sleep than high aerobic capacity runners (HCR). Asterisks indicate statistically significant differences between HCR and LCR rats. There were no differences in the rapid eye movement (REM) phase of sleep. (A ) Differences in sleep as a function of rat strain were apparent across 24 h of continuous sleep/wake recordings. (B ) There was no significant difference in the amount of time spent asleep or awake during the dark phase of the light-dark cycle. (C ) The sleep/wake differences between LCR and HCR rats resulted from differences in arousal state distribution during the light phase, when these nocturnal animals normally sleep. Data summarize eight 24-h recordings from HCR rats and eight 24-h recordings from LCR rats.