It is known as biorhythm to the cycle of physiological phenomena that repeats periodically and incident on the mood, emotion and feelings of humans. Biorhythms, therefore, influence people’s behavior.

Many times the idea of biorhythm is associated with the concept of biological rhythm: the oscillation of the parameters of biology according to environmental conditions and an internal clock. In the specific case of biorhythm, it refers to behavioral conditioning that comes from physiological cycles that are repeated over time.

This means that some vital questions of people could be predicted according to mathematical cycles. The existence of three biorhythm cycles is generally postulated: an intellectual cycle that lasts 33 days, an emotional cycle that lasts for 28 days, and a physical cycle that lasts 23 days. These cycles oscillate in a sine wave.

Many argue that biorhythms constitute pseudoscience. However, there are those who believe that there are periods of weakness, strength or greater sensitivity and therefore try to determine them using a biorhythmic chart. Thus, in theory, it is possible to know which are the favorable days for the development of certain activities, with the aim of making better use of time and energy.

This arrangement in three well-defined cycles serves many people to try to organize their lives in such a way that stress does not prevent them from moving forward smoothly. Since they believe in a system to predict the best time to carry out each type of activity, they rely on it and avoid failed attempts, minimizing the chances of failure or frustration.

As expressed in a previous paragraph, each of these cycles oscillates between two extremes, the high and the low, drawing a sine wave. Those days in which the line crosses the axis, that is to say when between the values is zero and the sign is inverted, can be considered *critical*; In other words, it is the moment in which the levels of uncertainty and risk reach their peaks, so it is not convenient to act without a well-drawn plan.

Apart from the three cycles mentioned above, experts in the field theorize about the existence of others, which may be longer or shorter, and to find them they rely on the concept of linear combination, a mathematical expression that is obtained by adding products of elements grouped in pairs (for example: taking an element from a set and multiplying it by one from another; this adds to the multiplication of two other similar elements, and so on).

The calculation of the three main cycles is not very complex, although it is necessary to memorize the structure of the equations and to know the way in which it should be taken to the calculator or the computer to avoid order errors. Basically, the sine of the following expression must be calculated: 2πt / d, where *t* is the number of days that have elapsed since the birth of the subject, and *d*, the one that corresponds to the cycle to be calculated (which can have the values 23, 28 or 33). Its use shows us, for example, every few days each cycle is repeated or the combinations that occur between them.

It is important to note that biological rhythms, studied by chronobiology, are recognized by science. Most physicians, however, believe that associating these rhythms with cycles known as biorhythms lacks scientific justification. It is even said that biorhythm is similar to numerology.