Altered timing of hamstring muscle action in anterior cruciate ligament deficient patients

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Abstract
Recent studies indicate that the hamstrings are essen tial antagonists in ACL deficient patients. In order to evaluate muscle coordination under physiologic condi tions, nine patients with arthroscopically verified total ACL ruptures were compared with nine control volun teers. This comparison was made from electromy ograms of the thigh muscles and heel contact record ings made while walking on a treadmill. While walking on a horizontal level, the patient's muscle activity did not differ from controls, but when the knee load was increased by walking uphill, the hamstring muscles in patients were activated signifi cantly earlier than among controls. It is proposed that an altered muscle coordination is probably essential in ACL deficient patients to secure knee stability. This study suggests a new approach to investigate the coordination of muscles under physiologic conditions in ACL deficient patients, and may guide rehabilitation programs in the future.