Accuracy of Biodex system 3 pro computerized dynamometer in passive mode

A specific experimental design has been developed to determine the accuracy of the Biodex system 3 pro dynamometer in passive mode. Five cyclic stretching repetitions were imposed to an elastic rubber band at different velocities using the dynamometer, and the torque produced was measured using both the dynamometer and external force and position sensors. Velocity patterns performed by the dynamometer were also characterized and our results show that these patterns were reliable (ICC=1.00). The torque measured with the dynamometer and the sensors were reliable (ICC=1.00), although significant differences were observed between both methods. However, the measured torque standard error was velocity independent and was lower than 0.33 Nm. Moreover, regressions between the two torque measurements were close to the axes-bisector (r=1.00, slope: 1.01+/-0.01, y-intercept: -0.36+/-0.22 Nm). Finally, our results showed decreases in torque during the five cycles, but these decreases were not due to the dynamometer. It can be concluded that the dynamometer performed valid torque measurements in passive mode, and was an accurate tool to determine passive mechanical properties of the musculo-articular system. However, some discrepancies between the programmed and the measured speed profiles have been observed when approaching the speed limit of the system.