WORK HOURS, SLEEPINESS AND THE UNDERLYING MECHANISMS

Severe subjective and physiological sleepiness occur in night work, af flict almost all individuals and are associated with a performance imp airment severe enough to explain night-work accident data. The alertne ss deficit is caused by the displacement of work to the circadian phas e which is least conducive to alert behaviour, by extension of the tim e spent awake and by the reduction of sleep length (due to circadian i nterference with sleep). Sleepiness will be extreme when the three cau ses are operative simultaneously. The three factors may be used quanti tatively to predict sleepiness.