Introduction: Cycling underwater is a low impact exercise and become an important component of therapy, patients in orthopedic or neurological disabilities, elderly people and injured athletes. Currently, the power output is not available to measure during cycling underwater and to increase the intensity; subjects need to increase the revolutions per minute (RPM). Moreover, blades connected to the bottom bracket of the stationary bicycle increases the frontal surface area (FSA) against the water. Therefore, the aim of this study was to determine the physiological responses during incremental cycling test underwater in a stationary bicycle that has a possibility to change the length of FSA