The assessment of human dynamic muscular function: a comparison of isoinertial and isokinetic tests

This investigation compared the relationship of isokinetic and isoinertial tests of muscular function to dynamic upper body performances. The electromiyographic activity of each of the tests of muscular function, as recorded by surface electrodes, were examined to determine whether neural differences underlie the ability of the test to relate to performance. Twenty four subjects performed isokinetic and isoinertial tests of muscular function in a bench press movement. The isokinetic tests were performed at velocities of 60, 90 and 120 deg/s while the isoinertial tests were performed at loads of 30%, 60% and 130% of the one repetition maximum. Subjects also performed the following tests of dynamic performance: a maximum one repetition bench press (1 RM), a seated shotput throw and two drop bench press throws from a height of 0.25 m at various loads. Forces/torques, displacement and electromyographic data were recorded from the isoinertial and isokinetic tests. Both the isoinertial and isokinetic parameters were related to the various measures of upper body performance (r = 0.33-0.94), however, neither was superior at predicting performance. Further, the relationship between the tests of muscular function were consistently high (r = 0.75-0.88). This was the case, even though the magnitude of the EMG signals were significantly higher in the isoinertial, as compared to the isokinetic tests. It is postulated that structural considerations, such as a specific testing position, rather than neural factors, underlie the observed results. These results support previous research which has reported the existence of a generality of strength across dynamic testing modalities.