The infradian rhythm includes essential biological cycles that last longer than 24 hours. Their frequency is thus below that of one day. The term is derived from the Latin words infra (under) and this (day). These chronobiological rhythms include, for example, the year-long processes of bird migration, the rutting season and the seasonal change of hair and feathers. They are also known as circannual rhythms. This also includes winter rest, the sexual cycle and rhythms that last about a lunar month (circalunar rhythm).
Biological rhythms can be divided into two main types. In addition to the infradins, these are the circadian rhythms, which extend over 24 hours and are the most important for humans. These include the sleep-wake rhythm and, for example, the rhythm of the plant leaf movements.
Ultradian cycles that are shorter than 24 hours are also important. They can be exemplified by the feeding cycles of field mice. The semilunar rhythm, on the other hand, is oriented towards the tides and is important for fish and their spawning habits, for example. It extends over 14.25 days and reaches its middle between two spring tides. The time of 12.5 hours between ebb and flow is called the circatidal rhythm. The people in the Wadden Sea, in particular, follow it.
Thanks to modern chronobiology, infradian rhythms are now being researched very carefully. It is associated with many important questions for people in the social medicine field.The diverse effects of shift work are an example of this. Furthermore, today many psychotropic drugs influence the daily rhythm of humans. Psychiatric clinical pictures have a serious influence on the circadian rhythm.
In general, today's life and work are moving further and further away from the so-called biological clock. In addition to the increasing shift work, a growing lack of light is also a cause of this change. In addition, frequent journeys across time zones have a strong influence on the circadian rhythm. The connection between these developments and psychiatric illnesses such as depression cannot be denied. Chronobiology as a relatively young science tries to research the effects of disturbed natural rhythms and to make them largely controllable.
The circalunar rhythm, which is based on the phases of the moon, has a special meaning. As part of the infradian rhythm, it describes the 29.5 day phase cycle of the moon. The astonishing reactions of some animals to these natural rhythms can be seen in the bristle worms. In the Mediterranean, some species of them mate reliably during a full moon. The palolo worm also follows the circalunar rhythms. Just before the new moon, he sheds his abdomen. This contains the germ cells and moves to the surface of the water, where sperm and egg cells are released for fertilization at sunrise.
The New World Spearfish (Grunion) is also perfectly adjusted to the infradian rhythm. It spawns in the coastal sand shortly after the spring tide. At the next flood, the spawning grounds are flushed and the larvae of the animal get into the open sea water. This process is repeated about every two weeks, depending on the full moon or new moon.
The female sexual cycle of humans and animals with ovulation and periods also represents a typical infradian rhythm. The male rut is geared towards this. In addition, the infradian rhythm of many mammals is also associated with a certain annual rhythm. This in turn cannot be determined in humans.
If the infradian rhythm of humans is interrupted or strongly shifted, this can lead to infertility in women, for example. Studies have shown that high levels of stress from constant shift or night work or extended working hours can make pregnancy more difficult. Women are receptive in periods that are essentially similar to the cycles of the moon and tides. If the infradian rhythm of the woman is intact, she releases the sex hormones in such a way that her fertility is guaranteed to an optimal degree. Any serious disturbance of this rhythm is at the expense of fertility and health in general.
The permanent alternation between tension and relaxation is also integrated into the human infradian rhythm. If this constant change is observed and consciously accepted, it means less stress in the daily work routine. The human metabolism is also used to certain rhythms and reacts with defensive behavior when the usual course of time gets mixed up. According to their “internal clock”, after an active phase (work, sport etc.) of 90 to 120 minutes, every person regularly needs a rest phase of 20 to 30 minutes. If this infradian rhythm is adhered to, long-term performance remains at the best possible level.
The human organism is naturally used to accepting these rhythms. With certain reactions such as yawning, drowsiness and lack of concentration, he draws attention to disturbances in these rhythmic processes. If the desire for a break is ignored, the body develops stress hormones beyond the usual level, which have a more or less negative effect on the circulation and well-being. Viewed over a longer period of time, numerous physical and mental illnesses are favored in this way.