What is a biorhythm?

Biorhythm is the theory that our bodies follow regular biological cycles that influence our physical, emotional, and intellectual state over time.

The Three Main Cycles

According to this theory, there are three cycles that begin at birth and oscillate continuously:

Physical (23 days): influences energy, strength, endurance, and coordination.
Emotional (28 days): affects mood, sensitivity, creativity, and well-being.
Intellectual (33 days): related to memory, reasoning, attention, and learning ability.

Each cycle alternates between positive (high) and negative (low) phases, and critical days (when the cycle crosses the zero line), which are moments of greater instability.

Origin

The theory was developed in the late 19th and early 20th centuries, mainly by physicians Wilhelm Fliess and Hermann Swoboda, and popularized by Friedrich Teltscher.

Is it worth taking seriously?

From a scientific point of view, there is no solid evidence to support the validity of biorhythms as a predictive system. Controlled studies have found no significant correlation between predicted cycles and people’s actual performance. The scientific community considers the theory to be pseudoscience.

This does not mean that biological rhythms do not exist — in fact, they do exist and are well documented, such as the circadian rhythm (a ~24-hour cycle that regulates sleep, hormones, and body temperature). The difference is that these real rhythms are studied by chronobiology, an established science, and do not follow the fixed cycles proposed by the biorhythm theory.

Biorhythms in Depth
How Cycles Work (in theory)

Each cycle is represented by a sine wave that oscillates between +100% and -100%. The formula used is:

sin(2π × days_of_life / cycle_duration)

The “critical days” occur when the curve crosses zero — these would be the moments of greatest risk or unpredictability, as the body would be in transition between phases.

Some proponents of the theory have added extra cycles to the original model:

Intuitive (38 days): perception, unconscious, instincts
Spiritual (53 days): values and purpose in life
Aesthetic (43 days): artistic sensitivity
Historical Context

The theory has roots in the late 19th century. Wilhelm Fliess, a physician and close friend of Sigmund Freud, observed patterns of 23 and 28 days in his patients and believed that these numbers had universal significance. Freud even became interested in the subject for a period. Hermann Swoboda, a psychologist from Vienna, independently reached similar conclusions. Decades later, Friedrich Teltscher identified the 33-day cycle.

The theory gained great popularity in the 1970s and 1980s, with books, calculators, and even software dedicated to charting people’s moods.

Why do people believe this?

Several psychological factors explain the persistence of the belief:

Barnum/Forer effect: we tend to accept vague and generic descriptions as if they were personalized for us.
Confirmation bias: we remember the days when we felt bad and the chart said “low phase,” and we forget when it doesn’t match.
Need for control: the idea of being able to predict how we will feel is very psychologically appealing.
What science really says

Several studies were conducted in the 1970s–90s to test the theory, and the results were consistently negative. None of them found a correlation above chance between predicted cycles and events such as accidents, athletic performance, test results, or mood.

In 1998, psychologist Terence Hines published a comprehensive review of all the literature on the subject and concluded that the theory of biorhythms is without empirical basis.

Real Biological Rhythms

Biology does indeed have rhythms — but they are far more complex and variable than the theory suggests:

Real Rhythm Duration What it regulates
Circadian ~24 hours Sleep, temperature, hormones
Ultradian < 24 hours REM sleep cycles, hunger
Infradian > 24 hours Menstrual cycle, seasonal immunity
Circannual ~1 year Seasonal mood (e.g., seasonal depression)

These rhythms are studied by chronobiology, which is a legitimate and rapidly developing science. Researchers such as Jeffrey Hall, Michael Rosbash, and Michael Young won the Nobel Prize in Physiology in 2017 for unraveling the molecular mechanisms of the circadian clock.

In summary

Biorhythms as a popular theory are a 20th-century cultural product without scientific backing. But the interest they generated helped popularize the idea — scientifically valid — that biological time matters. Today we know that when we sleep, eat, exercise, and take medication can be just as important as how much we do these things.

Possible Indirect Behaviors Reported by Some Users

Important: the following does not represent proven effects of the biorhythm theory. No scientific evidence supports these outcomes. These are informal behavioral patterns some people report when using biorhythm charts as a personal organization tool — not as a medical or psychological resource.

Greater attention to one’s own state The simple act of tracking how you feel day by day — even using a biorhythm chart as a reference — may encourage the habit of paying more attention to one’s physical and emotional state. This type of self-awareness has independent value, and is not a result attributed to the biorhythm theory itself.

Personal planning and organization Some people use cycles as a loose personal reference to distribute tasks throughout the week. Even though the cycles have no scientific validity, the underlying habit of planning with awareness of one’s own energy levels is a broadly recognized organizational practice.

Reduced pressure on difficult days Some users report feeling less self-critical on hard days by attributing them to external factors. It is worth noting, however, that this can also discourage problem-solving and self-improvement, and should not replace professional psychological support when needed.

Note on the placebo effect The placebo effect is a documented psychological and physiological phenomenon studied in controlled clinical settings. Its mention here is purely informational and does not imply that biorhythms produce any validated therapeutic benefit. Biorhythms are not a treatment, therapy, or medical intervention of any kind.

The Risks of Taking It Too Seriously

On the other hand, there are real pitfalls if the theory is used rigidly:

Negative self-fulfilling prophecy: believing it will be a “bad day” can make you act less carefully or with less motivation.
Important decisions based on pseudoscience: avoiding surgeries, interviews, or business decisions based on charts with no scientific validity is genuinely risky.
Substitution of real care: using biorhythms in place of medical or psychological monitoring to understand mood and energy variations can delay important diagnoses.
What Really Works

If your interest in biorhythms stems from a desire to better understand your own energy and well-being cycles, there are scientifically backed approaches that deliver real results:

Mood and energy diary — noting how you feel each day for a few weeks reveals real personal patterns.
Sleep hygiene — respecting your circadian rhythm is one of the most effective interventions for energy and mood.
Applied chronobiology — adapting study, exercise, and meal times to your chronotype (whether you are more of a morning or evening person) has solid scientific evidence.
Psychological support — for more intense mood swings, a mental health professional can identify real patterns and offer appropriate, evidence-based support.

In short, the value of engaging with biorhythms lies less in the theory itself and more in the habit of self-reflection it may encourage in some individuals. The theory lacks scientific foundation, but the underlying intention — to better understand oneself — is a genuinely worthwhile pursuit.