Effect Of Forced Adduction On Emg Activity Of The Vastus Medialis Oblique And Vastus Lateralis

Abstract

Atrophy of the vastus medialis oblique (VMO) muscle often occurs after knee injury. Since traditional quadriceps exercises do not selectively increase VMO activity, adduction is often added. The literature is divided as to the effectiveness of this practice. Few studies have explored this effect during isotonic closed chain exercises. Additionally, no information is available on the amount of force that must be applied during adduction to elicit a greater response from the VMO than the vastus lateralis (VL) muscle. PURPOSE: To examine the effects of several levels of forced adduction on the electrical activation of the VMO and VL during open and closed kinetic chain exercises and to investigate these effects by gender. METHODS: Twenty subjects, 10 males and 10 females had their VMO and VL electromyographical activity measured during an isometric maximal voluntary contraction (IMC), straight leg raises (SLR), knee extensions (KE), and single leg quarter squats (QS) while using three different levels of forced adduction (0, 10, and 15 lbs). RESULTS: The level of adduction had no significant effect on the activation of the peak or mean VMO, VL, or VMO/VL ratio. The different exercises did have a significant effect on VMO and VL activity. QS and KE elicited a significantly higher peak VMO, VL, and VMO/VL ratio than SLR. When analyzed by gender, males showed a greater peak VMO for KE and QS compared to SLR while females showed a greater peak VMO for KE compared to SLR and QS. Peak VMO/VL ratio revealed a significant gender difference with males showing a greater KE and QS response than females. Comparing the exercises to the IMC showed a significantly higher peak VMO/VL ratio during the QS exercise at 10 and 15 lbs adduction for males and 0 lbs adduction for females. CONCLUSIONS: Although adduction did not significantly increase VMO activity, the findings do suggest that different exercises may elicit a stronger peak response from the VMO than the VL when compared to a maximal contraction. Single-leg QS may be a preferred exercise during VMO rehabilitation. This study also showed males and females respond differently to exercises with the different levels of adduction. Because of this, care should be taken when prescribing rehabilitation for the VMO between males and females; a generic technique may not be successful for both genders.