Figure 1.

Study protocol: schematic overview of the study protocol (top); time schedule of sleep interventions for subjects who always go to sleep at 24:00 (middle); and pattern diagram for each trial (bottom). All subjects ate the same meals; dinner was curry and rice; breakfast was a jelly drink. On the day of the experiment, subjects were restricted from caffeine drinks, alcohol consumption, strenuous exercise, and naps, and had restrictions on television and smartphone use from dinner to the end of the experiment the next day.