The physical biorhythm lasts 23 days and affects our physical factors like: endurance, coordination, strength, speed, resistance to disease and generally sensation of physical well-being. The next cycle is the emotional which is 28 days long. It influences our nervous system and is responsible for: mental health, sensitivity, creativity, mood, perception of the world and generally all emotional states.

The last one is the intellectual biorhythm. It takes 33 days and influences our memory, alertness, receptivity to knowledge, logical function of the mind, speed of learning, accuracy of computation etc.

On the day of birth all three cycles start to raise from zero point and they look like a Sinus curve. At the middle of each cycle they cross zero point again and start to fall. At the end of cycle the point zero is recrossed into a positive phase and the whole process begins again. Generally, on positive days abilities associated with each cycle are high and on negative days - they are low. The most unstable times are the ''critical days'' and ''zero days'' when biorhythm crosses its point zero. The first day of the cycle is called ''the zero day'' and the middle day of the cycle is called ''the critical day''. During those days the abilities vary wildly, from extremely high to extremely low. You must beware of those days! Your system has the lowest efficiency. In that period you are susceptible to accidents and adversity. For people seriously interested in theory of Biorhythms we highly recommend the book by Bernard Gittelson ''Biorhythm - A Personal Science''.