A biorhythm is one of three cyclic rhythms that are supposed by some to govern human behaviour.
The physical cycle lasts 23 days, the emotional cycle lasts 28 days and the intellectual cycle lasts 33 days. All three cycles are drawn, apparently arbitrarily, as sinusoidal curves that start with their minimum values at the birth of each individual. (This is one of its dubious assumptions.) Therefore the value of each cycle can be calculated at any given time in the life of an individual, and there are web sites that do exactly that.
The purpose of biorhythms is to enable the calculation of auspicious days for performing or avoiding various activities. By definition, one's birth is an extremely inauspicious event, as is the day about 58 years later when the three cycles are again synchronised at their minimum values! The theory is assumed to apply only to humans.
wikipedia.org dumped 2003-03-17 with terodump