2020 Volume 41 Pages 185-191
The current study investigated the relationships between muscle cross-sectional areas of trunk muscles and dynamic balance ability in the sitting position for 14 healthy young men in order to obtain knowledge about improvement of performance in sit-ski. The cross-sectional images of the erector spinae muscle, the abdominal rectus muscle and the abdominal internal-external oblique muscles were obtained by extended field-of-view ultrasound imaging. Their cross-sectional areas were determined using ImageJ. To evaluate the dynamic balance ability in the sitting position, a floor reaction force meter was fixed on a six-axis motion base used as a disturbance applier, and a chair ski seat was placed on it. Participants sat on the seat, and the following disturbances were applied: 1） disturbances to move the basal plane laterally, 2） disturbances to tilt the basal plane, and 3） disturbances to add both simultaneously. Because the dominant arm of all participants was the right arm, the laterality was first confirmed for all parameters. As a result, there was no laterality in each parameter. When investigating the relationships between the muscle cross-sectional areas of each muscle and the dynamic balance ability in the sitting position, therefore, the left and right mean values were used. There was a significant correlation between the muscle cross-sectional area of the abdominal rectus muscle and the dynamic balance ability. On the other hand, the muscle cross-sectional area of the abdominal rectus muscle was smaller than the others. Consequently, it could not be asserted that the amount of the muscle cross-sectional area of the trunk muscle affects the dynamic balance ability in the sitting position positively.
