The purpose of this study was to investigate the timing of muscle activities of the trunk and the lower extremities in rapid vertical jumping. [Subjects] Twelve healthy men (mean age 22.3±0.8 (SD) years old) participated in this study. [Methods] The subjects were asked to jump vertically as quickly as possible when a red light placed 2 m ahead of them was turned on. The time from light stimulus to both feet aloft was measured in the gastrocnemius muscle, the biceps femoris muscle, the internal oblique muscle, and the multifidus muscle using surface electromyography. [Results] A high correlation was found only in the internal oblique muscle for the relationship between whole body reaction time and the muscle contraction inception time. No significant differences were found in the contraction inception time among the 4 muscles. [Conclusion] We suggest that a person capable of using his/her internal oblique muscle can start the whole body reaction more quickly. We clarified that muscle activities had almost the same timing among the measured muscles.
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