Comparison between the endogenous circadian rhythm in PAI-1 and day/night rhythm in PAI-1. Comparison between the endogenous circadian rhythm in PAI-1 assessed during the twelve 20-hour cycles of the FD protocol (A) and the day/night rhythm in PAI-1 assessed during the second 24-hour baseline day including sleep/wake, fasting/feeding, supine/upright, rest/activity, and dark/light cycle (B). Figures are aligned according to the approximate average corresponding clock time of the circadian profile (ie, 0 circadian degrees equates to ∼4:30 am and 3 hours prior to habitual scheduled awakening in these participants). In order to allow comparison of absolute values, subjects’ data were not normalized (in contrast to Figure 1). Timing of meals, sleep, and test battery (gray bars) are indicated for the baseline day (data for FD protocol were all collected during the test battery). B, breakfast; L, lunch; D, dinner; S, snack. M, mental stress test (10-minute computerized serial addition test); T, head-up tilt; E, exercise. Top x-axis (A), corresponding average clock time; top x-axis (B), average clock time. During the baseline day, participants were in semirecumbent posture until T, in varied postures throughout the remainder of the day, and remained lying down throughout the sleep episode. Error bars represent standard error of the mean.