The aim of this study was to quantify the muscle activity patterns during bounding movement on a G-ball. Ten male university students, who were unskilled at the bounding movement on a G-ball, were participated in this study. The subjects were required to execute bounding movement in a seated position on a G-ball. Electromyogram (EMG) of erector spine muscle (ES) at L4, which is directly related to the postural control in the bounding movement, and acceleration at C7 were recorded. Difference between peak timing in bounding cycle of acceleration and ES EMG was examined with both mean of inter- and intra-subject. No significant difference between the inter-subject mean of the peak timings was detected. On the other hand, significant difference between the peak timing of acceleration and ES EMG was detected in intra-subject mean of five subjects, and two of the five showed the preceded EMG peak relative to that of the acceleration and the other showed delayed EMG peak. Therefore, in unskilled bounding movement on a G-ball, three patterns of ES activities were identified; preceded peak, delayed peak and simultaneous peak relative to that of acceleration. We concluded that the knowledge of the variety of ES activity pattern in unskilled bounding movement could be a key of appropriate coaching for novice in G-ball exercises.
