Biorhythm
A biorhythm is a hypothetical cyclic pattern of alterations in physiology, emotions, and/or intellect. "Bio" pertains to life and "rhythm" pertains to the flow with regular movement.  Critics assert that there is no conclusive evidence to back its claims, and that as such it is a form of pseudoscience.

# Basic theory
The theory of biorhythms claims that one's life is affected by rhythmic biological cycles, and seeks to make predictions regarding these cycles and the personal ease of carrying out tasks related to the cycles. These inherent rhythms are said to control or initiate various biological processes and are classically composed of three cyclic rhythms that are said to govern human behavior and demonstrate innate periodicity in natural physiological change: the physical, the emotional, and the intellectual (or mental) cycles. Others claim there are additional rhythms, some of which may be combinations of the three primary cycles. Some proponents think that biorhythms may be potentially related to bioelectricity and its interactions in the body.
- Physical cycle (23 days; Circavigintan)
coordination
strength
well-being
- coordination
- strength
- well-being
- Emotional cycle (28 days; Circatrigintan)
creativity
sensitivity
mood
perception
awareness
- creativity
- sensitivity
- mood
- perception
- awareness
- Intellectual cycle (33 days; Circatrigintan)
alertness
analytical functioning
logical analysis
memory or recall
communication
- alertness
- analytical functioning
- logical analysis
- memory or recall
- communication
Basic rhythms follow certain facets of physiological cycles, though they may include others, and the details may vary depending on the source. The three classical cycles of biorhythms are endogenous infradian rhythms.  The theory's basis lies in physiological and emotional cycles. They are often represented graphically as either symmetric or asymmetric waveforms, though most theories rely on symmetric forms. The most commonly used form is the sinusoidal waveform, which is thought to be a plausible representation of a bioelectric activity cycle. Due to this sinusoidal nature, the cyclical flow of bioelectric activity undergoes periodic reverses in direction.  Each cycle oscillates between a positive phase  and a negative phase , during which bioelectric activity strengthens and weakens. The waveforms start, in most theories, at the neutral baseline (0%) at the time of birth of each individual.  Each day that the waveform again crosses this baseline is dubbed a critical day, which means that tasks in the domain of the cycle are far more erratic than on other non-critical days. The purpose of mapping the biorhythmic cycles is to enable the calculation of critical days for performing or avoiding various activities.
The classical definition (derivatives of the original theory exist) states that one's birth is an unfavorable circumstantial event, as is the day about 58 years later when the three cycles are again synchronised at their minimum values.  According to the classical definition, the theory is assumed to apply only to humans.  In the classical theory, the value of each cycle can be calculated at any given time in the life of an individual, and there are web sites that do exactly that.

# Related terminology

## Biological rhythm cycles

# Application
In the workplace, railroads and airlines have experimented the most with biorhythms. A pilot describes the Japanese and American attitudes towards biorhythms. He acknowledges, researching his pilot logbook, that his greatest errors of judgment occurred during critical days, but concludes that an awareness of one's critical days and paying extra attention is sufficient to ensure safety. A former United Airlines pilot and user of the  Biorhythms for Windows program confirms that United Airlines used biorhythms until the mid-1990s, while the Nippon Express air freight still used biorhythms.
Charting biorhythms for personal use was popular in the United States during the 1970s; many places (especially video arcades and amusement areas) had a biorhythm machine that provided charts upon entry of date of birth.

# History
The classical theory originated at the turn of the 19th century,  between 1897 and 1902, from observational research.
Hermann Swoboda, professor of psychology at the University of Vienna, who was researching periodic variations in fevers, looked into the possibility of a rhythmic change in mood and health.  He collected data on reaction to pain, outbreak of fevers, illnesses, asthma, heart attacks, and recurrent dreams. He concluded that there was a 23-day physical cycle and a 28-day emotional cycle.
Wilhelm Fliess, a nose and throat specialist and reportedly a numerologist, was independently researching the occurrences of fevers, recurrent illnesses and deaths in his patients. He too came to the conclusion that there was a 23 and a 28-day rhythm. Fliess' theories were of great interest and importance to Sigmund Freud during his early work in developing his psychoanalytic concepts.
Alfred Teltscher, professor of engineering at the University of Innsbruck, observed that his students' good days and bad days followed a rhythmic pattern of 33 days. Teltscher found that the brain's ability to absorb, mental ability, and alertness ran in 33 day cycles. In the 1920s, Dr. Rexford Hersey (psychologist; Pennsylvania, America) also reportedly made contributions to the classical theory.
These three biorhythms compose the classical theory. The classical theory has been studied, especially in Germany, Japan, and the United States, with conflicting results. Various modern derivatives exist of the classical theory.

# Plausibility
Proponents of biorhythmics call it an established interdisciplinary area of scientific endeavor which is still speculative, alternatively, a protoscience. Critics state that biorhythms are based only upon numerological associations. The plausibility of biorhythmics is contested by mathematicians, biologists and other scientists. The most basic assertion is that, even if physiological rhythms do exist, why would they begin precisely on the day of our birth?
Biorhythms have echoes of chronobiology, the study of circadian and other rhythms. Through medical research, doctors have found that there are periodicity and rhythms in a person's lifespan, although few doctors believe they correspond to those described as "biorhythms". Biochronometry has shown that rhythm and cycles such as the circadian (from Latin circa diem; literally, "about a day") exist. To proponents, these discoveries (among others) demonstrate that people are affected by physiological, emotional and intellectual rhythms (though the exact relationships to the biorhythm cycles are not precisely understood). Studies regarding the effects of biorhythm on the human condition are still conducted.
The Biorhythm theory is often treated as falsely claiming scientific validity. Biorhythm critics' responses range from opposing it as harmful to ignoring it or treating it as entertainment. Some of the criticisms of the various theories in the category of biorhythmics are:
- The choices of periodical function, frequency and phase are arbitrary.
- The assumption is made that the cycles are the same for everyone.
- The frequency is assumed to be constant.
- Evidence tends to be anecdotal.
- Arguments are made based in ignorance of number theory.
- Tests of the hypothesis have basic flaws.
- The quantitative generalizations of complex human behavior are inadequate.
- Hypotheses are not formulated precisely.
- Experimental data fail peer review.
- Experiments cannot be replicated.
- Some unscrupulous practitioners resemble professional fortune-telling fraud artists.
Some biorhythm critics say that biorhythms can be thrown off by such occurrences in the calendar as the beginning of the new year, holidays, or something as simple as the start of the week.
There have been some three dozen studies supporting biorhythm theory but all of them have suffered from methodological and statistical errors (Hines, 1998). An examination of some 134 biorhythm studies found that the theory is not valid (Hines, 1998). (Hines, Terence M. "Comprehensive Review of Biorhythm Theory," Psychological Reports, 1998, 83, 19-64.)

# Calculation
The formulae for the curves are
- physical: \sin(2\pi t/23),
- emotional: \sin(2\pi t/28) and
- intellectual: \sin(2\pi t/33),
where t indicates the number of days since birth.

# Patents
- U.S. Patent 4,960,980 - Bioclock calculating device for human body
- U.S. Patent 4,625,732 - Apparatus for measuring the actual psychophysiological condition
- U.S. Patent 4,551,620 - Biorhythms analog computer-calendar
- U.S. Patent 4,465,077 - Apparatus and method of determining fertility status
- U.S. Patent 4,184,202 - Biorhythm computer
- U.S. Patent 4,101,962 - Electronic calculator for determining biorhythm data