Reliability and Validity of the Omnitron Hydraulic Resistance Exercise and Testing Device

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Abstract
This study assessed the measurement reliability and validity of the Hydra-Fitness Omnitron, a microprocessor-controlled isokinetic ergometer that provides concentric resistance for dynamic extension and flexion movements as well as resistance for isometric contractions. Maximal peak torque output measured by the Omnitron and strain gauge devices connected to the apparatus were compared in 26 physically active males who were tested over 3 days for isometric knee extension and isokinetic knee flexion/extension at two resistance levels. Maximal torque outputs remained stable on days 2 and 3 (p < 0.05), and in-traclass reliability yielded r = 0.94 to 0.98. There was no difference between the slopes of the regression lines for the different experimental conditions (p > 0.05). There was significant improvement between day 1 and days 2 and 3 that corresponded to a combination of a training and learning effect. Thus, one practice session was necessary to obtain reliable individual differences. The validity correlations between peak torque output measured from the Omnitron and strain gauges were greater than r = 0.94. There was a small discrepancy (0.44 to 0.88 Nm) between the two measuring devices that can be explained by the difference in shank pad positioning that accomodates for different segment lengths. We conclude that reliability and validity were excellent over a wide range of torque outputs measured during maximal isometric and maximal dynamic double concentric flexion and extension movements.