A validational study of programmable time-locked actigraphy as an instrumented test of fatigue

The proposition that general ambulatory activity, as well as nocturnal motility, are affected by fatigue was tested experimentally in a sample of 24 healthy male college students. An actigraph programmed to record in 1-minute epochs was worn by each subject--at the waist during waking hours and transferred to the nondominant wrist for sleep--for 19 consecutive days and nights of continuous activity measurement. Subjects completed a longitudinal experimental course that included 1 week of baseline measurements, followed by 2 experimental weeks during which their sleep was restricted on separate weekends. Thus, intrasubject replication was employed. The experimental fatigue-induction manipulation required the subject to get no more than 5 hours sleep on Friday, Saturday, and Sunday nights. Parameters of daily distributions of 1-minute activity scores post-fatigue were compared to subjects\u27 own baselines measurements. Mean activity was found to decrease while the frequency of low-activity scores simultaneously increased (which was reflected in a measure of skewness) on days, as well as nights, post-fatigue-induction. As a conservative estimate, fatigue effects appeared to last for one day and three nights. Thus, support was found for the hypothesis that fatigue influences activity. Alternative explanations concerning the potential operation of other influences on subjects\u27 activity were explored. The finding of a relationship between activity and fatigue from restricted sleep has implications for actigraphy investigations generally in that future investigators and clinicians may wish to control for or monitor the influence of this variable. This finding also suggests the potential utility of activity measurement for naturalistic assessment of the frequency and duration of fatigue within clinical populations