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.

Physical cycle: 23 days ( coordination, strength, well-being).
Emotional cycle: 28 days ( creativity,sensitivity, mood, perception, awareness ).
Intellectual cycle: 33 days ( alertness, analytical functioning, logical analysis, memory or recall, communication ).