Individual, phase, and weekly variations in daily cycles of wrist activity in freeliving humans.

Wrist activity was monitored in 17 college students for 11-15 days each. Records of individuals had distinctive patterns, like fingerprints. The subjects all exhibited daily cycles in their activity with activity during the daytime and with period lengths close to 24 h. There was individual variation in average phase (onset 5.3 h, offset 4.5 h, acrophase 6.1 h). Individual subjects all showed 7-day oscillations in their activity patterns associated with the weekly work-leisure schedules. During the leisure weekends, the subjects as a group had a 2.1-h delay in onset, a 1.5-h delay in acrophase, and a 0.8-h shortening in alpha.