Short crank cycle ergometry.

The change in knee angle during cycling was mathematically analyzed. It was determined that if the crank length of the cycle ergometer was shortened, the arc of knee motion necessary to cycle could be reduced. A computer program was written to represent the above mathematical model utilizing a patient's lower limb lengths to generate an individualized, range of motion profile. A custom cycle ergometer was built with interchangeable crank lengths of 80 mm, 110 mm, 140 mm, and 170 mm. This device can be adjusted to achieve a desired range of motion for a specific patient. The above custom cycle ergometer can be used on early postoperative knee patients who are unable to ride a conventional cycle ergometer because of a lack of knee motion or on patients who require a limited arc of motion in their postoperative therapy protocol. J Orthop Sports Phys Ther 1991;13(2):95-100.