Biorhythm, inner clock
The research on the human biorhythm is based on two assumptions. Firstly, a human consists of a physical, an intellectual, and an emotional component. Secondly, the entire condition of a human is bound to periodical changes that can be depicted as sine oscillations between two extreme points. All three curves start at birth. The have different durations, so that there are various combinations of highs or lows of one, two, or all three components.