The Correlation between the Muscle Activity and Joint Angle of the Lower Extremity According to the Changes in Stance Width during a Lifting Task

[Purpose] This study examined the correlation between the muscle activities and joint angle of the hip and knee according to the changes in stance width during a lifting task. [Subjects and Methods] The subjects of this study were 15 healthy students. A three-dimensional motion analyzer (SMART-E, BTS, Italy) was used to measure the joint angles of hip and knee during lifting. An 8-channel electromyograph (8-EMG) (Pocket EMG, BTS, Italy) was used to measure muscle activities of the erector spinae, gluteus maximus, rectus femoris, and tibialis anterior during lifting. The collected data were analyzed using the Pearson-test and SPSS 18.0. [Result] The muscle activity of the tibialis anterior was significantly decreased by increasing the stance width (r= -0.285). Muscle activity of the erector spinae was significantly decreased by increasing the knee angle (r= -0.444). The muscle activity of the gluteus maximus was significantly increased by increasing the muscle activity of the tibialis anterior (r= 0.295). [Conclusion] Efficient lifting is possible when stance width and knee flexion are increased, which results in reduced muscle activity of the tibialis anterior and the erector spinae. Lifting is facilitated when the muscle activities of the gluteus maximus and tibialis anterior are correlated.