The Effect of Restricted Hip Extension on Muscle Activity During Functional Movements

Abstract

Background: Hip flexor tightness is a common problem affecting both active and sedentary individuals and can lead to the development of movement deficiencies potentially resulting in altered muscle activity around the hip joint. The overhead squat, inline lunge, and single leg step-up are common functional movements used to asses for movement deficiencies. The purpose of the study was to compare surface electromyography (sEMG) in the rectus femoris (RF), gluteus maximus (GM), biceps femoris (RF), and semitendinosus (ST) muscles and GM:BF co-activation ratio during the over-head squat, in-line lunge, and step-up between healthy females with and without hip flexor tightness. Methods: Participants were screened for hip flexor tightness using the modified Thomas Test and classified into a tight hip flexor and non-tight hip flexor group. Muscle activity data was collected using sEMG on the RF, GM, BF, and ST muscles during three functional movements: The over-head squat, in-line lunge, and step-up. Results: There were no statically significant differences in muscles between those with hip flexor tightness and healthy controls during the three tested movements. However, those with hip flexor tightness displayed greater hamstring utilization during all movements (Hedges g = 0.37 - 0.73). Conclusions: Those who have hip flexor tightness appear to adopt a more hamstring-based movement strategy to complete functional movements. More research is warranted to determine the extent to which hip flexor tightness affects functional movement patterns and muscle activity surrounding the hip joint.