Modifications to hydra-gym equipment provide for clinically useful strength measurements

Modifications were made to the Series III-311 Omnikinetic Hydra-Gym apparatus (Hydra-Fitness Industries Inc., Belton, TX) in an effort to provide relatively inexpensive yet clinically useful isokinetic strength measurements. Signal transmission and processing functions were installed to calculate relevant strength characteristics for knee extension/flexion motions. Results from the modified Hydra-Gym were compared with matched procedures on the Kin-Com (model 500-10, Chattecx Corporation, Chattanooga, TN). Subjects (N = 10) performed three maximal concentric right knee extension/flexion cycles at different resistance settings (2, 4, and 6) on the Hydra-Gym and the corresponding angular velocities on the Kin-Com (190, 125, and 40 degrees/sec, respectively). Each subject completed eight testing sessions, four on each dynamometer. A five-way analysis of variance on the peak torque data revealed no significant difference between dynamometers; however, there was a significant interaction between dynamometer and extension/flexion measurements. The variance in angle of peak torque data was significantly different between dynamometers, with Hydra-Gym showing superior reproducibility (p < 0.005). Mechanical differences between dynamometers produced slightly different, though comparable and consistent, measurement values. Care must be taken when evaluating hamstring/quadriceps ratios from the Hydra-Gym because the interaction noticed between dynamometer and extension/flexion may exaggerate muscle imbalances. In summary, modifications to the Hydra-Gym appear to provide clinicians with a reliable and clinically useful strength testing alternative.