Date of Award


Document Type

Scholarly Project

Degree Name

Doctor of Physical Therapy (DPT)


Physical Therapy

First Advisor

Thomas Mohr


Anterior Cruciate Ligament Injuries; Electromyography; Hamstring Muscles -- physiology; Quadriceps Muscle -- physiology


Background and Purpose. The purpose of this pilot study was to find if there was a difference in the activation and firing time of the quadriceps (vastus medialis and vastus lateralis) compared to activation times of the hamstrings (biceps femoris and semitendinosus) in active males and females.

Methods. Subjects consisted of two male and two female athletes in good physical condition with no previous knee pathologies. During each of the trials, the muscle activity of each muscle was recorded. The EMG activity recorded using a Noraxon TeleMy02400 G2 telemetry unit with a sampling rate of 1 kHz which was transmitted to a TeloMyo PC interface card connected to a laptop computer. Data analysis was performed using the MyoResearch XP 1.07 software. EMG activity was recorded by placing Blue Sensor (model M-OO-S) surface electrodes on the skin over each of the muscles under study. Before applying the electrodes, skin was cleansed with isopropyl alcohol. The electrodes were placed in accordance with standardized lead positions. A foot switch placed inside the shoe was used to determine when the subject's foot was on or off the ground. The electrodes were placed on the vastus medialis, vastus lateralis, biceps femoris, and semitendinosus. The participants were then asked to perform a series of five consecutive jumps. EMG data was collected during five consecutive jumps from each participant. A marker was placed at the beginning and end of each jump to indicate the time that the foot was on the floor between jumps. A Noraxon Standard Timing Analysis was used to measure onset time and firing order for the four muscles. A threshold of both 2 and 3 standard deviations (SD) was used as the criteria for onset activity. A Noraxon Standard EMG Analysis was used to compare the muscle activity during the jump activity with the MVC activity and reported as a percent of the MVC.

Results. The results of this study showed the male subjects splitting dominance between hamstring and quadriceps muscle activation in regards to which muscle fired first when landing after a jump. Female subjects showed greater quadriceps activity than hamstring activity, and the quadriceps appeared first in the firing order. One female participant showed very little hamstring electromyography (EMG) activity upon landing a jump. Strength training that targets the hamstring muscle group, and that maintains a good quadriceps to hamstring ratio should be utilized to try and prevent injury of the ACL, especially in female athletes.

Conclusion. Further research is needed to confirm these conclusions and demonstrate clinical relevance.