Differences in force production on various isotonic loading devices

The purpose of this study was to compare the force required to lift a given weight throughout the range of knee extension on the N-K Table, Nautilus, and Universal knee extension machines. A static measurement was taken with a force gauge and chart recorder at every 5 deg throughout the machine's range of motion using a 20-lb weight. Results revealed significant differences between the forces on each machine at each angle that was measured (p < 0.0001). The Nautilus machine's force curve ascended throughout the range from 9.7 to 20.2 lbs. The Universal machine's force curve descended from 41.1 to 27.9 lbs. The force curve of the N-K Table ascended from 8.8 to 27.5 lbs and then descended to 15.4 lbs, with an offset angle of 64 deg. Clinicians are advised to consider the differences in these machines in order to optimize the efficiency of available equipment and minimize the risk of injury.