By the Law of Periodical Repetition, everything which has happened once must happen again and again…. ~ American humorist Mark Twain
The body has biological rhythms, which should not be confused with the pseudoscience labeled biorhythms, which has been around at least since the late 19th century.
According to the biorhythm hypothesis, the human system goes through 3 biological cycles: a 23-day physical strength cycle; a 28-day emotional cycle; and a 33-day intellectual prowess cycle.
As a practice, biorhythms supposedly can be calculated from date of birth to predict susceptibility to accidents, or conversely, opportunities of achievement.
However congruent with the concept of circadian rhythm, biorhythms are to biological rhythms as astrology is to astronomy. Its clockwork cogency may appeal, but biorhythms scientifically flounder for lack of evidence.