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Etymology: Gk, bios, life, logos, science, rhythmos
the periodic recurrence of a biologic phenomenon, such as the respiratory cycle, the sleep cycle, or the menstrual cycle. Also called biorhythm.
A hypothetical biologic rhythm, which is said to be set at birth.
The biorhythm theory was first proposed by H Swoboda and W Fleiss, a contemporary and colleague of Sigmund Freud; proponents of the biorhythm theory believe there are three distinct cycles: a physical cycle of 23 days—which corresponds to co-ordination, immunity, self-confidence, and strength; an emotional cycle of 28 days; and an intellectual cycle of 33 days, all of which are defined by a sine wave; “critical periods” are believed to exist as an individual crosses the middle of a cycle, either from a high to a low, or vice versa.
Cyclical variations in physiologic and biochemical function, level of activity and emotional state. Circadian biorhythms have a cycle of about 24 hrs; ultradian rhythms are < 1 day; infradian rhythms are greater than one day and may be up to weeks or months.