ABSTRACT
Farm work has always been associated with long working hours, starting at sunrise and ending at sunset. In the waking hours, the body is naturally ready for physical and mental work; during the night, it relaxes and sleeps. Flexible working hours are a form of work organization. The control of the number of working hours, and their scheduling, is on the individual; the overriding requirement is to get work done on time. The regulation of alertness, wakefulness, sleepiness, sleep, and many physiological functions appears to be under the control of two internal clocks of the body: one controls sleep and wakefulness; the other, physiological functions, such as body temperature. The brain and the muscles are the human organs that show the largest changes from sleep to wakefulness: their electrical activities have allowed for well-established techniques of observation. The amplitude of electroencephalography signals is measured in microvolts; the amplitude rises as consciousness falls from alert wakefulness through drowsiness to deep sleep.
