A Monark cycle ergometer is used in physiological studies to measure work done and power. In this paper, the accuracy of a Monark rope-braked cycle ergometer was examined for a Wingate anaerobic test (WAnT). The traditional method of determining brake torque fails to take into account rope-brake theory and, as the brake torque is used to determine the moment of inertia of the flywheel, a second error is introduced into the calculation to determine the work done or power. In this study, the rope tensions were measured to determine the actual brake torque. A deceleration test was carried out to determine the moment of inertia of the system. The work done by subjects of different masses was calculated for various accelerations and it was found that the traditional calculations overestimate work done and power by between 12% and 14.7%.