Fig. 1
The blue dashed curve represents sleep pressure (process S), which increases during wakefulness and decreases during sleep, and the orange curve represents circadian rhythms (process C), which regulate the sleep-wake cycle. The gray shaded area represents optimal sleep duration, which occurs when high sleep pressure coincides with circadian rhythms that promote sleep onset. This figure illustrates the temporal alignment of sleep pressure and circadian rhythm, which is central to this study’s hypothesis about how the timing of physical activity affects sleep efficiency.
