Extension and flexion torque variability in ACL deficiency.

PURPOSE: To evaluate possible differences in knee extension and flexion torque variability in the anterior cruciate ligament-deficient (ACLD) leg and their dependence on muscle length and visual feedback (VF). Although a knee extension torque deficit is found in the ACLD leg, there is no evidence that variability in submaximal isometric knee extension and flexion torque is affected in the ACLD leg or that it depends on VF.

METHODS: All tests were performed using 13 untrained men with unilateral ACL rupture. Isometric knee extension torques at 90(o) and 120(o) and knee flexion torques at 90(o), 120(o) and 140(o) were evaluated in healthy and ACLD legs. Isometric torque variability at 20% of maximal force was evaluated with or without VF. The coefficients of variation (CV) and permutation entropies (PE) were used to calculate submaximal isometric torque variability.

RESULTS: Healthy legs had significantly greater isometric torques at 90(o) and 120(o) knee angles during knee extension compared with ACLD legs. There were no differences between healthy and ACLD legs in torque variability in knee extension and flexion with or without VF. The PE of knee extension torque at knee angles of 90(o) and 120(o) was significantly (P < 0.05) greater in healthy legs.

CONCLUSIONS: The effect of ACL deficiency on variability (CV) in submaximal isometric knee extension and flexion torque was not significant. However, PE of knee extension submaximal torque was significantly greater in the healthy leg than in the ACLD leg. When estimating ACL deficit, it is important to measure not only isometric maximal torque but also torque variability and complexity using nonlinear tool during submaximal isometric tasks.

LEVEL OF EVIDENCE: III.