Abstract
The present study determined the trajectory of center of gravity (COG), joint movement, and muscle activity of the side-step motion for five different side-step lengths (SSLs) in 9 healthy males (mean age, 20.3 ± 0.7 y). The SSLs examined were 25%, 50%, 75%, 100%, and 125% of the distance between the anterior superior iliac spine and the medial malleolus. Electromyograms, the ground reaction force, and the three-dimensional coordinates of the bone index were analyzed during the side-step motion. We calculated the trajectory of the COG, joint movement, muscle activity, and the moment arm (the difference between the COG and the center of pressure positions). It was found that the COG was transferred using different strategies at 25% SSL and 50% SSL, with knee extension and plantar flexion of the ankle joint required to generate propulsion power at 50% SSL. Moreover, moment arm, which acted as a propulsion power toward the side, increased as SSL increased. The activities of gluteus medius and gluteus maximus also indicated high activities during the side-step motion. In conclusion, both the propulsion power generated by extension of the lower extremity and the moment of gravity were important to increase SSL. Moreover, the moment-arm increment with increasing SSL intensified postural instability. Thus, good control of posture is necessary when taking longer side-steps.
