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

• Core and hip strength is significantly correlated with knee kinematics in females.
• Hip abductor strength was the best predictor of the Frontal Plane Projection Angle.
• Clinicians should consider hip strength when assessing single leg squat kinematics.

ObjectiveThe 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.ParticipantsForty healthy females participated in this study.MethodsAn 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°.ResultsAll 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).ConclusionClinicians 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.