Biorhythm (pseudoscience)

The biorhythm theory is the pseudoscientific idea that peoples' daily lives are significantly affected by rhythmic cycles with periods of exactly 23, 28 and 33 days, typically a 23-day physical cycle, a 28-day emotional cycle, and a 33-day intellectual cycle. The idea was developed by German otolaryngologist Wilhelm Fliess in the late 19th century, and was popularized in the United States in the late 1970s.

Source: Wikipedia — Biorhythm (pseudoscience) (CC BY-SA 4.0)