Validity analysis of the Biodex System 3 dynamometer under static and isokinetic conditions

Isokinetic dynamometers are frequently used as training devices. They are also regularly employed to measure the characteristics of skeletal muscles under dynamic conditions. The combination of published data of such measurements and the authors' own experience led to the present investigation of the validity of measurements performed using the Biodex System 3 dynamometer. Two individual dynamometers of the same type were used. A calibration technique was used to test the validity of measured torque and the angular coordinate of the position of the lever arm of the dynamometer under static conditions. The results of measurements performed under dynamic (isokinetic) conditions were verified by comparing numerical values of tests provided in the Biodex report and raw data collected directly from the measuring computer of the same isokinetic machine. The shapes of experimentally determined characteristics of torque Mmax(ω) and power P(ω) were also analysed, taking into consideration their conformity with the laws of thermodynamics and known properties of skeletal muscles. The static tests showed that the indications of the Biodex System 3 dynamometer lay within the error range specified by the manufacturer. Therefore, the results of static measurements can be considered accurate. According to the isokinetic tests, the values of angular velocity were also accurate. However, indications of torque and power were much less accurate, justifying the uncertainty over whether they can be considered true results of measurement.