Effects of Increased Gluteus Muscle Activation on Hip and Trunk Kinematics during Single-leg Landing

Abstract

The gluteus maximus (GM) has a triplanar function at the hip joint. It was hypothesized that increased GM activation before and after foot contact (FC) on landing would affect triplanar hip and trunk kinematics and anterior cruciate ligament (ACL) injury risk. PURPOSE: To examine how increased GM activation before and after FC affect hip angles and trunk inclination during single-leg landing. METHODS: A double-leg drop jump from a 30-cm box, followed by single-leg landing onto a force plate, was performed by 13 males and 15 females in both control (CC) and experimental conditions (EC). In EC, transcutaneous electrical stimulation was applied to increase GM activation immediately before FC and during single-leg landing. Kinetic and kinematic data were collected using a force plate and 3-dimensional electromagnetic motion tracking system, respectively. Hip joint angles and sacrum and thorax inclination angles in space on FC, peak ground reaction force (GRFpk), and peak knee extensor moment (KEMpk) during single-leg landing were calculated. Comparisons were performed using two-way (sex×conditions) repeated measures analysis of variance with a significance level < .05. RESULTS: The hip joint exhibited more abduction (EC vs. CC at FC, GRFpk, and KEMpk, respectively: -13.2 ± 7.8° vs. -9.5 ± 6.3°, -8.9 ± 7.7° vs. -4.9 ± 6.8°, -3.3 ± 8.9° vs. -.2 ± 6.5°) and external rotation (-14.8 ± 8.5° vs. -9.8 ± 9.9°, -8.0 ± 3.6° vs. -3.6 ± 9.7°, -6.1 ± 9.7° vs. -1.6 ± 11.2°) at all time points in EC than in CC. The sacrum showed more lateral inclination toward the supporting leg at all time points (14.3 ± 6.4° vs. 11.1 ± 6.4°, 12.1 ± 6.4° vs. 9.0 ± 6.1°, 8.9 ± 7.1° vs. 6.7 ± 6.2°) and more erect position at KEMpk in EC (-1.0 ± 10.6°) than at CC (-4.6 ± 10.5°). No significant differences were observed in thoracic inclination angles. No significant interactions were observed among all variables. CONCLUSIONS: Increased GM before and after FC on single- leg landing may have positive effects on frontal and transverse plane hip motion to reduce ACL injury risk. However, excessive GM activation may result in excessive trunk lean toward the supporting leg and more erect position, which increase risk for ACL loading. Thus, appropriate GM activation is necessary to protect the ACL during single-leg landing.