Date of Award


Document Type

Scholarly Project

Degree Name

Doctor of Physical Therapy (DPT)


Physical Therapy

First Advisor

Mark Romanick


Anterior Cruciate Ligament Injuries -- etiology; Risk Factors


Purpose/Background: This goal of this study was to reach a bottom up understanding of ACL injury occurrence. Subtalar position during single leg stance may affect the muscles associated with the knee joint and promote ACL injury. The muscle activity of six muscles of the leg, thigh, and hip were analyzed during a single leg squat with the foot on surfaces of 10 degrees decline, five degrees decline, neutral, and 5 degrees incline, and 10 degrees incline.

Methods: Seventeen healthy participants between the ages of 18 and 30 performed five rhythmically timed repetitions of single leg squats on surfaces of 10 degrees decline, five degrees decline, neutral, and 5 degrees incline, and 10 degrees incline to simulate pronation with declined surfaces and supination with inclined surfaces. Electrodes were placed over selected muscles and data on their activity was collected and evaluated.

Results: Muscle activity increased with increasing inclination and declination. Percent MVC increased the most in ten degrees of subtalar pronation in four of six tested muscles: anterior tibialis, lateral gastrocnemius, gluteus maximus and gluteus medius. However, due to study limitations, high variability, and large standard deviations we are unable to make a confident conclusion. Lateral gastrocnemius, biceps femoris and gluteus maximus were found to be statistically significance using Friedman’s.

Conclusions: A pronated subtalar position results in the highest %MVC in the majority of muscles of the lower extremity proximal to the ankle joint. This suggests that subtalar position affects muscles and joints more proximal which may result in an increased risk of ACL injury in this position. More research is needed to determine the effect subtalar position on susceptibility to ACL injury as our study has many limitations.