Quadriceps activation during knee extension exercises in patients with ACLpathologies

This study assessed muscle inhibition in patients with chronic anterior cru ciate Ligament (ACL) deficiency or ACL reconstruction. A series of protocol s were tested for their effectiveness in increasing activity of the individ ual knee extensor muscles and decreasing muscle inhibition of the whole qua driceps group. Quadriceps muscle inhibition was measured by superimposing a n electrical twitch onto the quadriceps muscle during a maximal voluntary k nee 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 ACL-deficient patients compared to ACL-reconstructed patients. When a knee extension was pet-formed in comb ination with a hip extension, there was a significant increase, p < 0.05, i n activation of the vastus medialis and vastus lateralis muscles compared t o isolated knee extension. The use of an anti-shear device, designed to hel p stabilize the ACL-deficient knee, resulted in increased inhibition in the quadriceps muscle. Furthermore, a relatively more complete activation of t he vasti compared to the rectus femoris was achieved during a fatiguing iso metric contraction. Based on the results of this study, it is concluded tha t performing knee extension in combination with hip extension, or performin g fatiguing knee extensor contractions, may be more effective in fully acti vating the vasti muscles than an isolated knee extensor contraction. Traini ng interventions are needed to establish whether these exercise protocols a re 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.