Fig. 1.

Sleep and circadian timing. Average timing of sleep episodes (boxes), melatonin onset (black upward triangles), and melatonin offset (black downward triangles). Error bars are SEM. P values are calculated by mixed model ANOVAs. Melatonin onset significantly delayed in the 5-h condition (P < 0.01 versus BL and 9 h), whereas melatonin offset was similar for conditions (P = 0.77). Durations between melatonin onset and bedtime and between melatonin onset and melatonin offset were similar for conditions (both P > 0.39), whereas duration between melatonin offset and wake time was significantly longer in the 5-h condition (P < 0.001 versus BL and 9 h).