Two commonly used measures to calculate exercise intensity (*exercise intensity*) are oxygen intake (*oxygen intake*) and heart rate (*heart rate*). Oxygen intake is the amount of oxygen that enters the body during respiration. Oxygen intake per kilogram of body weight per minute (referred to as VO2) can be used to calculate exercise intensity. The measurement of VO2 requires expertise and complex and large tools. Heart rate (*heart rate*; HR) is also often used to calculate exercise intensity. Heart rate measurement is easy to do with a smaller and easier to do device, so the use of the heart rate formula is more often used for lay use. One formula that is often used is the Karvonen formula. This formula is often used in the field of physical exercise and medical rehabilitation.

One of the variables in the Karvonen formula is the maximum heart rate (HR max), which is a certain heart rate that a person reaches when he pushes his body to the limit of his physical endurance. Measurement of HR max directly on a person will cause a heavy physical burden for a person, so it is necessary to use a certain formula to estimate HR max.

The formula commonly used is: HR max = 220 – age

The above age is the patient’s age. The formula above is only an approximation, does not always precisely determine HR max. In addition to the formula above, there are several other formulas with varying accuracy. In general, the weakness of such formulas is that they are too age dependent, and do not take into account the situation of the general population.

She, J., Nakamura, H., Makino, K. et al. Selection of suitable maximum-heart-rate formulas for use with Karvonen formula to calculate exercise intensity. int. J. Autom. Comput. (2015) 12:62. https://doi.org/10.1007/s11633-014-0824-3