**Abstract**

Sarcopenia is currently defined as a progressive and generalized skeletal muscle disorder that occurs with advancing age and is associated with an increased likelihood of adverse outcomes. Low levels of measures for muscle strength, muscle quantity, and physical performance define sarcopenia. In this chapter, we will see that the prevalence of a low value of physical performance will be different according to the method used to measure this parameter, and thus, it would be foreseeable to think that the prevalence of sarcopenia will also be different according to the method used. However, despite the differences found in physical performance, we will show that the prevalence of sarcopenia appears to be regardless of the method used for physical performance, and therefore, how is it possible that having a significant difference in the prevalence of physical performance depending on the method chosen, the prevalence of sarcopenia has an almost perfect agreement? To answer these questions, a new simplified model is studied, defining sarcopenia as low muscle strength and low muscle mass and without taking physical performance into account. Finally, we will see that, indeed, physical performance does not seem to be decisive or necessary for the diagnosis of sarcopenia.

**Keywords:** aging, prevalence, diagnosis, sarcopenia, EWGSOP
