The effects of foot angle and leg position on the activation levels of vastus medialis and vastus laterals

This study aimed to determine the influence of foot angle and leg position on the activation levels of vastus medialis (VM) and vastus lateralis (VL) muscles during two common leg extension exercises. Specifically, this study aimed to preferentially recruit VM by introducing a gentle stretch over the muscle, through the combination of thigh adduction and tibial external rotation (with the foot turned out to 45 degrees). Healthy and asymptomatic volunteers (N=29) performed two leg extension exercises, leg press and terminal leg extension, in two different foot positions (feet parallel/vertical, or foot turned out to 45 degrees) and with or without a component of thigh adduction achieved by placing a firm ball between the knees of the subject. Subjects included were participants of team sports. Outcome measures included: Peak EMG activation for VM and VL during the leg extension phase, normalised to MVC; Average EMG activation for VM and VL during the leg extension phase, normalised to MVC; and Knee flexion angle at the time of peak VM and VL activation. Data for each condition were compared using a three factor repeated measures ANOVA. Trends in the data revealed a tendency toward higher muscle activation during the closed kinetic chain exercise (leg press) compared to an open kinetic chain exercise (terminal leg extension). These peak activation values also occurred with the leg in a more flexed position during the leg press compared to the terminal leg extension exercise. However, it was also observed that turning the foot out to 45 degrees does not greatly influence muscle activation in a preferred direction. Furthermore, introducing a gentle stretch over the muscle by adding components of thigh adduction and leg external rotation (with the ball in place) was found to be ineffective in selectively activating VM under these experimental conditions. On the basis of these findings and within the limitations of this research, it was concluded that whilst dynamic quadriceps contractions are undertaken, altered limb or foot position towards tibial external rotation and hip adduction has no influence on preferential activation of VM in asymptomatic individuals.