Relationship between hip and core strength and frontal plane alignment during a single leg squat

Abstract

Objective: The purpose of this study was to examine the relationship between frontal plane kinematics of the single leg squat and strength of the trunk and hip in females. Participants: Forty healthy females participated in this study. Methods: An isometric "make" test using a dynamometer was used to assess peak force normalized to body weight for hip abduction, hip extension, hip external rotation, and a sidelying plank test. Two-dimensional software was used to analyze the frontal plane projection angle (FPPA) and pelvic angle during a single leg squat to 60°. Results: All 4 strength factors were significantly correlated with the FPPA, ranging from r=0.396 to r=0.466. During multiple regression analysis, hip abduction strength was the greatest predictor of the variation in FPPA at r2=0.22, p=0.002. Thus, hip abduction strength accounted for 22% of the variation in the FPPA during the single leg squat. The only strength factor demonstrating a significant correlation with the pelvic angle was hip extension strength (r=0.550, p<0.001). Conclusion: Clinicians should consider the role of the hip abductors, hip external rotators, hip extensors and core musculature on the impact on the FPPA during a single squat, with focus on the hip abductors.