Characteristics of the activities of the muscles surrounding the knee during single- leg squatting performed by patients with anterior cruciate ligament injury

Abstract

[Purpose] To investigate the characteristics of the activities of the muscles surrounding the knee during single-leg squatting performed by patients with anterior cruciate ligament (ACL) injury. [Subjects] Nine ACL injury patients and eight healthy subjects. [Method] The task was single-leg squats with knee flexion of 20 to 50 °, and the muscles investigated were the vastus medialis (VM), vastus lateralis (VL), and the inner and lateral hamstring muscles. For each of the muscles, we compared %MVC, the normalized value of the maximal voluntary contraction (MVC) obtained from the integrated electromyograms, of the injured and healthy sides of the patients, and the dominant side of the healthy subjects. [Results] Compared to the healthy side, %MVC of the injured side VM and VL were smaller, and those of the inner and lateral hamstrings were larger. [Conclusion] The activities of the knee muscles of ACL injury patients during single-leg squats suggest that these muscles function to stabilize anterior instability.