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The purpose of this study was to quantify the rate of force development (RFD) and maximum force in isometric, concentric, and stretch-shorten cycle contraction modes and to determine their relationships to sprint running performance. Fifteen athletic subjects performed a series of isometric, concentric, and stretch-shorten cycle RFD tests in an upright squat position using a modified Smith machine positioned over a force platform. The concentric and isometric tests were performed at both 110° and 150° knee angles. From the force data recorded, the maximum force, maximum RFD, force at 30 ms, and impulse at 100 ms were used as test variables. Subjects also ran a 30-m indoor sprint from a crouched start. Of the 20 force-time variables calculated, the concentric tests were the only ones significantly correlated to performance and able to effectively discriminate between good and poor performers. Isometric tests were unrelated to dynamic performance. This was suggested to be due to the large neural and mechanical differences between isometric and dynamic muscular actions. The results are strongly supportive of the use of concentric RFD tests but not isometric ones.
Wilson et al. (Tue,) studied this question.