Biorhythm
The biorhythm theory proposes that three biological cycles begin at birth and oscillate regularly throughout life: physical (23 days), emotional (28 days), and intellectual (33 days). Formulated by Wilhelm Fliess and Hermann Swoboda in the late 19th century; the intellectual cycle was added by Alfred Teltscher in 1928.
Scientific status
Controlled studies (Hines 1998; Bischoff 1980) found no correlation between biorhythms and performance, accidents, or health. The theory is classified as pseudoperiodicity in scientific consensus.