ANTERIOR CRUCIATE LIGAMENT INJURY AND HAMSTRINGS COACTIVATION

Two experiments were conducted to determine whether injury to the ante rior cruciate ligament influences coactivation patterns of the hamstri ngs during voluntary isometric knee extension. Normal patterns of hams trings coactivation were established in a control group during submaxi mum and maximum effort isometric knee extension torque at two knee fle xion angles. Subjects who had undergone anterior cruciate ligament rec onstructive surgery and a group of conservatively managed patients wer e studied using a modified protocol. It was predicted that (a) hamstri ngs coactivation patterns would vary significantly as a function of kn ee flexion angle, and (b) control and anterior cruciate ligament recon structed subjects would differ significantly from the anterior cruciat e ligament deficient subjects. Contrary to expectations, (a) hamstring s coactivation patterns were not significantly related to knee joint a ngle for any of the three groups, and (b) differences between hamstrin gs coactivation patterns of the anterior cruciate ligament deficient a nd anterior cruciate ligament reconstructed groups were not significan t. The hamstrings coactivation pattern of the combined anterior crucia te ligament group data was significantly different from control patter ns and characterized by significantly higher hamstrings coactivation. The coactivation may increase knee joint stability/stiffness and may b e a beneficial adaptation to the injury-related knee joint instability . The long-term effect of this adaptation on knee joint function is un known.