Biomechanical Analysis Of A Single-leg Squat With Isokinetic Resistive Force By A Novel Exercise Equipment

Abstract

Increased external knee valgus moment is a major factor in noncontact anterior cruciate ligament injury. Gluteal muscle activity is important for preventing excessive hip adduction motion and external knee valgus moment. To increase gluteal muscle activity during single-leg support, we devised a resistive single-leg squat (RSLS) exercise using a novel isokinetic exercise machine (ERIK ). RSLS is a closed kinetic chain exercise where the support leg performs a single-leg squat while sliding the opposite leg laterally against a resistive force. PURPOSE: To reveal the biomechanical and electromyographic (EMG) characteristics of the support leg during RSLS compared with those of a common single-leg squat (SLS). METHODS: Six asymptomatic female college students participated in this study. Participants performed RSLS and SLS. In RSLS, the movement speed of ERIK was 0.25 m/s and the reaching length was 80% of the SMD(spina malleollar distance). A motion capture system and force plate were used for motion analysis, and the support leg joint moments were calculated. Surface electrodes recorded EMG of support leg muscles. Average EMG amplitude during descent phase in both tasks was normalized by that during maximum voluntary contraction. The Wilcoxon signed-rank test was used for statistical analysis. RESULTS: In RSLS, hip adduction angle was significantly smaller (3.2±2.3° vs. 12.2±3.7°, p<0.05) and hip abduction angle was significantly larger (11.9±2.9° vs. 1.3±4.1°, p<0.05) than those in SLS. Motion patterns of the hip joint differed between RSLS and SLS. As descent motion progressed, hip abduction angle increased in RSLS, while hip adduction angle increased in SLS. External valgus moment occurred in 5 participants during SLS (0.2±0.2 Nm/kg) but in only 1 participant during RSLS. EMG activity of the gluteus medius was significantly higher in RSLS than in SLS (85±17% vs. 60±17%, p<0.05), as was that of the adductor longus muscle (35±18% vs. 23±13%, p<0.05). CONCLUSION: RSLS against isokinetic force with ERIK increased the load on the gluteus medius, and the alternate hip joint motion pattern seemed effective for preventing external knee valgus moment on the support leg. Supported by JSPS KAKENHI Grant No. 25282192.