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Core Strength and Lower Extremity Alignment during Single Leg Squats


Medicine & Science in Sports & Exercise: May 2006 - Volume 38 - Issue 5 - p 945-952
doi: 10.1249/01.mss.0000218140.05074.fa

Introduction/Purpose: Muscles of the trunk, hip, and knee influence the orientation of the lower extremity during weight bearing activities. The purpose of this study was threefold: first, to compare the orientation of the lower extremity during a single leg (SL) squat among male and female athletes; second, to compare the strength of muscle groups in the trunk, hips, and knees between these individuals; and third, to evaluate the association between trunk, hip, and knee strength and the orientation of the knee joint during this activity.

Methods: Twenty-four male and 22 female athletes participated in this study. Peak isometric torque was determined for the following muscle actions: trunk flexion, extension, and lateral flexion, hip abduction and external rotation, and knee flexion and extension. The frontal plane projection angle (FPPA) of the knee during a 45° SL squat was determined using photo editing software.

Results: Males and females moved in opposite directions during the SL squat test (F(1,42) = 5.05, P = 0.03). Females typically moved toward more extreme FPPA during SL squats (P = 0.056), while males tended to move toward more neutral alignment (P = 0.066). Females also generated less torque in all muscle groups, with the exception of trunk extension. The projection angle of the knee during the SL squat test was most closely associated with hip external rotation strength.

Conclusion: Using instruments suitable for a clinical setting, females were found to have greater FPPA and generally decreased trunk, hip, and knee isometric torque. Hip external rotation strength was most closely associated with the frontal plane projection angle.

1University of Delaware, Department of Physical Therapy, Newark, DE; 2Kentucky Sports Medicine Clinic, Lexington, KY; and 3Drayer Physical Therapy Inst., Hummelstown, PA

Address for correspondence: John D. Willson, MSPT, University of Delaware, Department of Physical Therapy, 305 McKinly Lab, Newark, DE 19716; E-mail:

Submitted for publication August 2005.

Accepted for publication December 2005.

©2006The American College of Sports Medicine