The Effect of Hip Flexor Tightness on Muscle Activity During Functional Movements and the Front Squat

Abstract

Muscular imbalances can be described as altered reciprocal inhibition by which an overactive agonist causes a decrease in neural drive and optimal recruitment to its functional antagonist (Clark et al., 2018), which can lead to synergistic dominance muscles that eventual ends in musculoskeletal injury and impaired performance (Jones & Bampouras, 2010; Kendall et al., 2005). The purpose of this study was to compare muscle activity in the rectus femoris (RF), biceps femoris (BF), semitendinosus (ST), and gluteus maximus (GM) muscles and GM:BF co-activation during the functional movements (N = 23) and in the front squat (N = 16) in females with and without hip flexor tightness. Mean muscle activity of the RF, BF, ST, and GM and GM:BF co-activation were not significantly different in females with and without hip flexor tightness during the overhead squat, in-line lunge, and forward step-up. However, individuals with hip flexor tightness displayed higher mean BF activation during the overhead squat, in-line lunge, and forward step-up. Mean ST was also higher in individuals with tight hip flexors during the overhead squat and forward step-up. More investigation on hip flexor tightness and hamstring activity is inquired, as previous literature has shown tight hip flexors may cause changes in the neuromuscular control of the lumbopelvic hip complex, specifically the BF. During both the ascending and descending phase during a 75% 1RM front squat, peak BF activity was significantly higher (p < .05) in resistance trained females with hip flexor tightness compared to those without. During the ascending phase, peak RF (p < .05) activity was significantly higher in those with hip flexor tightness compared to those without. Mean BF activity was significantly higher (p < .05) during the ascending phase of the front squat in those with hip flexor tightness compared to those without. The GM:BF co-activation ratio was significantly lower (p < .05) in those with hip flexor tightness compared to those without during both the ascending and descending phase of the front squat. Fitness professionals should consider providing a hip flexor stretching intervention to prevent over activation of the BF when selecting the front squat as a resistance training exercise. Providing a hip flexor stretching program to individuals who have tight hip flexors may decrease synergistic dominance of the hamstrings.