Sleep-wake cycle in shift workers on a "clockwise" and "counter-clockwise" rotation system.

The present study investigated the effects of a 5-day rotating work schedule in the advance, or "counter-clockwise", vs. delay, or "clockwise" direction, on subjective and objective measures of sleep-wake cycles. Twenty-two workers (mean age 27.5 +/- 4.6 years) were studied in the counter-clockwise direction, and 11 workers (mean age 29.83 +/- 5.93) were studied in the clockwise direction. Each worker was studied for a complete rotation cycle (20 days). Sleep-wake cycles were measured by wrist-worn actigraphs in 1-min bins. The clockwise direction was associated with significantly earlier sleep times during the night shift, and with a better synchronization of workers' sleep-wake cycles during night and evening shifts. The present results provide support to the claim that rotating shiftworkers can better adapt to clockwise than counter-clockwise rotations.