Pulse oximetry is used to determine the percentage saturation of oxygen in blood. Its main feature is that it is a noninvasive and relatively inexpensive. There are few studies relating physical activity and pulse oximetry with most abundant studies are clinical trials. The authors review the definition of pulse oximetry, the grounds upon which it is based. We review the application of pulse oximetry to maximum exercise testing, and the behavior of oxygen saturation in the blood for testing of maximum effort. In addition, different studies on the oxygen saturation values in blood during physical exercise and its correlation with other ventilatory variables. We analyze the consequences of the use of pulse oximetry in tests of maximal effort.