Relationship of isokinetic strength, power and ankle flexibility on underwater dolphin kick speed in competitive collegiate swimmers

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Background Several factors can contribute to increasing dolphin kick speed that muscle activation and simulation studies have been conducted. Although driving force can be generated by lower extremity strength and power, the relationship of isokinetic strength and power on dolphin kick speed remains unclear. Therefore, to examine a cause-and-effect relationship whether isokinetic strength and power, and ankle flexibility can contribute to increasing dolphin kick speed. Objective Twenty-one competitive collegiate male swimmers participated in this study. Methods The isokinetic strength (peak moment, Nm/kg) and power (time to peak moment, sec) of lower extremity, and ankle plantarflexion and dorsiflexion range of motion (ROM) were measured. Dolphin kick speed was measured by underwater video cameras (m/s). Results Underwater dolphin kick speed was affected by lower extremity strength and power of knee flexion, knee extension, and ankle dorsiflexion. Moreover, time to peak moment of knee flexion, knee extension, and ankle plantarflexion were also influencing factors. Conclusions This study suggests that velocity-based training could be suitable for improving strength and power for swimmers as the fast contraction speed of knee and ankle measures appeared to affect the dolphin kick speed in this study.