Quadriceps Activation During Knee Extension Exercises in Patients With ACL Pathologies

This study assessed muscle inhibition in patients with chronic anterior cruciate ligament (ACL) deficiency or ACL reconstruction. A series of protocols were tested for their effectiveness in increasing activity of the individual knee extensor muscles and decreasing muscle inhibition of the whole quadriceps group. Quadriceps muscle inhibition was measured by superimposing an electrical twitch onto the quadriceps muscle during a maximal voluntary knee extension. The level of activation of the individual knee extensor and knee flexor muscles was assessed via electromyography (EMG). Patients with ACL pathologies showed strength deficits and muscle inhibition in the knee extensors of the involved leg and the contralateral leg. Muscle inhibition was statistically significantly greater in ACLdeficient patients compared to ACL-reconstructed patients. When a knee extension was performed in combination with a hip extension, there was a significant increase, p < 0.05, in activation of the vastus medialis and vastus lateralis muscles compared to isolated knee extension. The use of an anti-shear device, designed to help stabilize the ACL-deficient knee, resulted in increased inhibition in the quadriceps muscle. Furthermore, a relatively more complete activation of the vasti compared to the rectus femoris was achieved during a fatiguing isometric contraction. Based on the results of this study, it is concluded that performing knee extension in combination with hip extension, or performing fatiguing knee extensor contractions, may be more effective in fully activating the vasti muscles than an isolated knee extensor contraction. Training interventions are needed to establish whether these exercise protocols are more effective than traditional rehabilitation approaches in decreasing muscle inhibition and achieving better functional recovery, including equal muscle strength in the injured and the contralateral leg.