Humans, like almost all living things, follow biological rhythms and cycles that have proven to be vital in the course of development. The relationships are explored by a fairly young scientific discipline, chronobiology. Particularly well known is the day-night rhythm, which regulates work and rest phases and is closely related to the distribution of light during the day in prehistoric times.
The inner clock as a clock generator
The same is true for summer and winter time, which influence the human body through the different lengths of time the sun shines on it – long periods of rest in winter minimize energy requirements and ensured survival even before prehistoric times. For this reason, it used to be thought that the organism reacted to an externally imposed rhythm.
In the meantime, however, we know that we have our own clock, the inner clock. Although it reacts to external influences, it continues to tick even when environmental factors such as light are switched off. It is controlled by processes such as the release of the hormone melatonin.
Biorhythms: Circulation of the body
The natural fluctuations of bodily functions as continuous changes in the organism occurring in recurrent cycles are called biorhythms. Important biorhythms in humans are:
- The sleep-wake rhythm
- The activity cycle
- The food intake and drinking rhythm
- The body temperature rhythm
- Endocrine rhythms
Other forms of a biological periodicity are the female cycle, the heartbeat and the renewal of blood cells.
These examples make it clear that humans are not only subject to a 24- to 25-hour daily rhythm controlled by the internal clock (circadian rhythm), but that other shorter (ultraradian rhythm) or longer-lasting cycles (infraradian rhythm) also play a role.
Biorhythmics as a pseudoscience
The term biorhythm is also used in the context of biorhythmics, a pseudoscience that assumes that life is wave-like subject to three rhythms of varying duration (between 23 and 33 days) – physical, emotional, and intellectual. Based on the date of birth and gender, models are used to calculate good and bad days.
This speculative form of regularities were propagated by the physician Wilhelm Fleiß at the beginning of the 20th century and lack scientific basis.
