Impact of Load Variation on Lower Limb Joint Torque during Overhead Squats

The purpose of this study was to examine the kinematic and kinetic changes in overhead squats (OHSs) with increasing loads and clarify the relationship between OHS movement and shoulder joint flexibility. Fourteen male college students randomly performed OHSs using 20% of their body mass (BM), 40% of their BM, and a plastic pipe (no load). The motion and ground reaction forces during OHSs were recorded. The relative peak torque of the hip under the 20% and 40% BM conditions during both negative and positive phases of the OHS was significantly greater than that under the no-load condition, while the relative peak torque of the knee did not increase. The relative peak torque of the hip was negatively correlated with the angles of the lower trunk at the lowest point of the center of mass (CM). In relation to the movement of the OHS and shoulder joint flexibility, a correlation was observed between the angle of the lower trunk at the lowest point of the CM and the shoulder flexibility test score (r = 0.561-0.598, p < 0.05), suggesting that a flexible shoulder joint could lead to the lower trunk leaning forward during the OHS. These results reveal that in the overhead squat, where the relative load to body weight is smaller compared to the normal squat, an increase in the load leads to an increase in hip torque without a corresponding increase in knee torque. Furthermore, the increase in hip torque is influenced by the angle of the lower trunk.