Date of Award

2012

Document Type

Scholarly Project

Degree Name

Doctor of Physical Therapy (DPT)

Department

Physical Therapy

First Advisor

Mark Romanick

Keywords

Anterior Cruciate Ligament Injuries -- etiology; Risk Factors

Abstract

Purpose/Background: Foot positioning during a single leg landing may affect the muscles above the ankle joint and promote positions of increased vulnerability to ACL injury. The purpose of the study was to analyze muscle activity of six muscles in the lower extremity during completion of a single leg squat on the subject’s dominant leg with the subtalar joint in 5 different positions.

Methods: Seventeen healthy males and females (ages 18‐30) performed five single leg squats in five foot positions: neutral, five degrees and ten degrees of declination, and five degrees and ten degrees of inclination. Electromyography data was collected from electrodes placed over each muscle. The declination mimicked pronation while the inclination mimicked supination of the foot/subtalar joint.

Results: The ten degree angle of pronation had the highest % MVC in four of the six muscles including anterior tibialis, lateral gastrocnemius, gluteus maximus and gluteus medius. With the high variability and large standard deviations, we are unable to make certain of our results. On average, the gluteus maximus muscle had the highest % MVC for all foot positions while the anterior tibialis had the lowest % MVC at 60.22. Lateral gastrocnemius, biceps femoris and gluteus maximus were the three muscles showing statistically significance using Friendman’s. Friedman’s was chosen as our study violated assumptions which prevented us from running a parametric test.

Conclusions: Pronation caused the highest % MVC which makes us suspect that the distal joint of the ankle can impact the degree of muscle activation above that joint. This also could be a position of vulnerability as it causes the muscles to contract more which could be secondary to instability, malalignment, or some other factor. More research is needed to study the effect of pronation as our study had several limitations.

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