Abstract
The quantification of worker performance changes during a shift is critical to establishing worker productivity. This investigation examined the existence of circadian rhythms in response variables that relate most meaningfully to the physiological and neurological state of the body for three subjects maintaining a resting posture for 25 hours on five separate occasions. Significant circadian variation ranging from 3% to 11% of the mean value was detected for elbow flexion strength, physiological tremor, simple reaction time, information processing rate and critical eye-hand tracking capacity.