INTRODUCTION: It has been reported that the transversus abdominis (TrA) activity precedes the agonistic muscle during movements of the limbs. The nature of the TrA activity during sports, however, has yet to be examined. The purpose of the present study was to clarify the activity pattern of the abdominal muscles during standing jump using wire electromyography.
METHODS: Thirteen healthy males participated in this study. Wire electrodes were inserted into the left TrA with the guidance of ultrasound imaging, surface electrodes were attached to the left rectus abdominis (RA) and external oblique (EO). The electromyographic activities and video images were recorded while each subject was performing standing jump at a distance equivalent to his own height. The experimental task was divided into the following 3 phases: from 200 ms prior to heel‐off to heel‐off (preparation phase); from heel‐off to toe‐off (push‐off phase); from toe‐off to 200 ms after toe‐off (jumping phase). For each muscle, reaction time relative to the toe‐off (0 s) and muscle activity level (%MVC) in each phase were determined, and evaluated using analysis of variance (ANOVA, p<.05).
RESULTS: The reaction times of the TrA, EO and RA were ‐349•} }64 ms, ‐279• }61 ms and ‐207• }70 ms, respectively. The onset of the TrA activation was earlier than that of the RA and EO activities. The activity level in all the muscles was significantly greater during the push‐off phase than the other phases.
DISCUSSION: These results imply that the TrA was activated first to enhance trunk stability, and the RA and EO were subsequently activated to generate the torque for a jumping movement. They also suggest that the abdominal muscles involving standing jump increase their activity levels during the push‐off phase.