Does the 'forbidden zone' for sleep onset influence morning shift sleep duration?

Shiftwork researchers have concentrated on the problems on the night shift, and have tended to neglect the truncation of sleep that can occur before morning, or 'early', shifts. We examined the sleep timing and duration between morning shifts of shiftworkers on a variety of shift systems. The extent of morning shift sleep truncation depended very largely on the time at which individuals had to leave home. Further, there was some suggestive evidence that the failure of individuals to compensate by going to sleep earlier was not simply due to social pressures to stay up. Rather it would appear to have depended, at least in part, on the biological clock determined 'forbidden zone' for sleep that occurs shortly before habitual sleep onset.