Concurrent validity of the FSL JumpMat for assessing leg extensor muscle function under stretch-shortening cycle conditions

The force plate has been the most commonly used device to assess leg extensor muscle function under stretch-shortening cycle conditions and is regarded as the gold standard in the measurement of vertical jump performance. Nonetheless, the cost and technical complexities of such a device precludes its routine use within many sporting environments spawning the development of many proposed alternatives. However, of these alternatives only contact mat devices can assess the full spectrum of muscle function due to their ability to quantify both jump height and ground contact time. PURPOSE: To determine the concurrent validity of the FSL JumpMat using a force plate as a criterion reference. METHODS: Four men (body mass 74.4±10.7 kg), competing in power sports (athletics, basketball, rugby) performed ten squat (SJ), countermovement (CMJ) and drop jumps (DJ) on the contact mat which was placed on a force plate. A force threshold of 5N was used to determine flight and contact phases. To ensure that measurements were not influenced by the weight of the contact mat the force plate was zeroed with the contact mat placed on the force plate. Flight time was used to quantify jump height using standard methods and the reactive strength index (RSI) was calculated as jump height divided by contact time. To examine the validity of the FSL JumpMat, the method of comparison as described by Bland and Altman was used. Differences were calculated by subtracting force plate measurements from those of the FSL JumpMat. RESULTS: Systematic bias was evident for all measures of jump performance (p0.05) between the absolute differences in jump height and the means revealed no evidence of heteroscedasticity for both SJ and CMJ. The resulting error interval was 1.93±1.87 cm and 1.92±2.09 cm for SJ and CMJ heights, respectively. A significant correlation (r=0.44; p