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: Anterior cruciate ligament (ACL) injuries at the knee are quite common, especially in the athletic population involved in sports in which jumping, landing, and cutting activities occur frequently. Previous studies have suggested that lower extremity muscle control plays a role in preventing these injuries. This study set out to determine if foot position influences muscle activation in the lower extremity and, by extension, possibly contributes to the risk of ACL injury. This project examined the activity of lower extremity muscles and the kinematics (movement patterns) of the lower extremity in various foot positions during a single-leg body lowering action. Lower extremity muscle activity influenced by foot position may alter the position of the knee, resulting in changes to stresses on the anterior cruciate ligament. This study attempted to determine whether foot position affects lower extremity muscle activity.

PROCEDURE/METHODS: The activity of the lower extremity muscles in various foot positions during a single-leg squat was measured using EMG analysis of the muscles influencing the knee. The six muscle we tested include gluteus maximus, gluteus medius, quadriceps femoris, biceps femoris, anterior tibialis, and lateral gastrocnemius The EMG recording device measured the electrical activity of the muscles during muscle action. Subjects performed a barefoot single-leg squat (to 45 to 60 degrees knee flexion) on the dominant stance leg 5 times, then returned to standing erect while weight bearing as EMG activity recorded for each of 5 different foot positions. Through varying foot ix positions during a single leg squat, this study helped explore a possible component to the mechanism of ACL injuries. The subjects performed 5 repetitions in each position, with data collection resetting after each position. Muscle activity was reported as a percentage of maximal voluntary contraction (MVC) of the respective muscle for each subject.

RESULTS: Data analysis was performed on each of the six muscle groups being tested (gluteus maximus, gluteus medius, biceps femoris, rectus femoris, lateral gastrocnemius, and anterior tibialis) comparing the baseline single leg squat to each of the four test positions (supination 5°, supination 10°, pronation 5°, pronation 10°). Our data analysis showed that there was no significant difference (p > 0.05) between the baseline muscle activity and five of the muscles tested: gluteus maximus, gluteus medius, biceps femoris, rectus femoris, and lateral gastrocnemius. The only significant difference (p < 0.05) found was in the anterior tibialis muscles.

CONCLUSION: The results from this study indicate that tibialis anterior was the only muscle that showed significant muscle activation in alternate foot positions. There was no significant difference found in any of the other muscles tested. Further research with more participants is needed to see if there maybe any difference in any of the other muscles tested.