Torque Production Profiles Post-ACL Reconstruction: Beyond Classic Maximum Peak Measures

PURPOSE: To develop a comprehensive profile of single-leg torque production in athletes post-ACL reconstruction (ACLR), as a first step toward examining the limitations of peak torque assessment and emphasizing a higher-resolution and more thorough evaluation of motor control during rehabilitation following ACLR. METHODS: Bilateral maximal isometric knee extension and flexion torque production was assessed in 30 individuals post-unilateral ACLR (18 Female; Age: 27.52 ± 11.23 years; Post-ACLR: 7.4 ± 2.7 months) using a dynamometer. Assessments included 3, 5-second trials at 30°, 60°, and 90° knee flexion, focusing on peak torque, torque decay rate, and decay shape (area under curve analysis). Statistical analysis employed paired samples t-tests and Wilcoxon signed-rank tests, based on data normality. RESULTS: Across all six conditions (3 positions on each limb), the ACLR limb consistently showed a significant reduction in peak torque (p ≤ .03) and a higher rate (p < .01) and different shape (i.e., smaller area under the curve) of torque decay (p < .01) compared to the contralateral, uninjured limb (see Table 1). This pattern indicates a universal deficiency in muscle strength and endurance post-ACLR. Varied effect sizes for torque production and decay rates across the six conditions revealed angle-specific recovery patterns, with distinct recovery trajectories for quadriceps and hamstrings and greater decay rates in the ACLR limb. CONCLUSION: The reliance on maximum torque as a solitary measure following ACLR may not fully represent a patient’s muscle health and function. A comprehensive torque curve analysis, incorporating peak torque, torque decay, and angle-specific recovery patterns, offers a more detailed understanding of neuromuscular deficiencies and endurance loss in the ACLR limb. This approach has the potential to inform targeted rehabilitation strategies, facilitating a safer and more effective return to athletic activity. Table 1. - Torque feature outcomes, p values and effect sizes across each condition for both the affected and unaffected legs. Isometric Condition Torque Feature Outcome by Side Extension Affected Unaffected p value Effect Size 30° Maximum (Nm) 71.45 (4.45) 89.87 (6.34) <.001w 0.71 Decay Rate (Nm/s) 1.51 (0.69) -1.21 (0.43) .001 w -0.64 AUC (Nm*s) 300.96 (9.53) 386.79 (8.59) <.001 w 0.99 60° Maximum (Nm) 114.92 (7.30) 149.49 (8.07) <.001 0.82 Decay Rate (Nm/s) 3.29 (0.03) 1.27 (0.03) <.001 -15.01 AUC (Nm*s) 465.80 (11.03) 649.29 (1.19) <.001 w 1.00 90° Maximum (Nm) 120.40 (8.47) 175.62 (11.56) <.001 0.94 Decay Rate (Nm/s) -0.38 (0.37) -1.58 (0.52) .007 w -0.55 AUC (Nm*s) 977.45 (2.39) 1408.48 (3.35) <.001 1.00 Flexion 30° Maximum (Nm) 98.25 (5.33) 108.53 (6.34) .002 0.61 Decay Rate (Nm/s) 0.33 (0.01) -1.25 (0.10) <.001 w -1.00 AUC (Nm*s) 405.77 (7.20) 445.01 (0.93) <.001 w 1.00 60° Maximum (Nm) 85.59 (4.94) 92.54 (5.23) .004 w 0.59 Decay Rate (Nm/s) -0.60 (0.02) -1.43 (0.02) <.001 -1.00 AUC (Nm*s) 357.32 (6.16) 401.75 (0.77) <.001 w 1.00 90° Maximum (Nm) 62.91 (4.27) 70.61 (4.74) .030 0.41 Decay Rate (Nm/s) -0.80 (0.01) -1.25 (0.01) <.001 w -1.00 AUC (Nm*s) 528.05 (1.20) 589.85 (1.48) <.001 11.27 Note. w denotes Wilcoxon signed-rank test; AUC = Area Under the Curve; All values presented as Mean (Standard Error); Effect size reported as Cohen’s d (r for Wilcoxon signed-rank test).