Figure 1. Study outline.

Each 21-day study period consisted of 4 days/3 nights of acclimation (Days 1-4), then a 14-day/14-night experimental phase (Days 5-18), followed by a 3-day/3-night recovery (Days 19-21). Participants completed both sleep restriction and control sleep conditions in randomized order, after a >3-month wash-out. Gray bar indicates 9 hours of time in bed (from 22:00 to 7:00), while red bar indicates 4 hours of time in bed (from 00:30 to 4:30).