Biorhythm is a popular theory formulated between the late 19th and early 20th centuries by physicians Wilhelm Fliess (Berlin, 1858-1928) and Hermann Swoboda (Vienna, 1873-1963), and later spread by Swiss Alfred Teltscher. It holds that three regular cycles govern the human being: a 23-day physical cycle, a 28-day emotional cycle and a 33-day intellectual cycle, all calculated from the date of birth.
The physical cycle (23 days) describes endurance, strength, coordination: the first half is considered "high", of charge; the second half "low", of recovery. The emotional cycle (28 days) describes mood, sensitivity, emotional creativity. The intellectual cycle (33 days) describes mental readiness, memory, learning ability. All start at birth and repeat indefinitely.
Days when a cycle crosses zero (passage from positive to negative or vice versa) are called "critical": biorhythm supporters consider them moments of greater vulnerability. When two or three cycles are critical on the same day (super-critical) sensitivity would be maximal.
Enter your date of birth and a reference date (today or a future day). The tool calculates the value of each of the three cycles, shows a graph with the three trends, signals any critical days and offers brief advice for the day.
That is the classic biorhythm hypothesis. In real biology we know there are cycles (24-hour circadian, women s ~28-day menstrual, seasonal cycles) but not linearly tied to birth date.
Consider the scientific basis is weak. More reliable cues come from body listening, resting heart rate, sleep quality and personalized training plans.
No. Biorhythm arose in medical-popular field and only refers to birth date as "phase 0". Astrology, instead, refers to planetary positions.