Quantifying Recovery After Anterior Cruciate Ligament Reconstruction Using the Torque- Velocity Relationship

Following anterior cruciate ligament reconstruction (ACLR), patients often display persistent deficits in quadriceps muscle strength that reduce quality of life and lead to long-term functional impairment. Historically, post-operative assessments of muscle function have focused on maximal isometric torque or peak torque at a single isokinetic velocity, neglecting the variety of demands placed on a muscle group across activities and the precision needed to guide clinical decision-making. The goal of this demonstration is to illustrate how isokinetic testing at different angular velocities can be used to characterize the torque-velocity relationship following ACLR. The protocol includes participant preparation, dynamometer setup, range-of-motion configuration, and alignment of key testing components, including chair position and dynamometer arm length. Strength assessment consists of isometric knee extension testing and concentric isokinetic knee extension and flexion testing at 60°/s, 180°/s, and 240°/s. For the two-point method, torque-velocity is calculated as the difference in normalized torque production between a slow and a fast testing velocity (e.g., 60°/s and 180°/s). For full multi-velocity characterization, peak torque values obtained at each velocity are exported to a spreadsheet or statistical software and analyzed using regression techniques. Previous results have demonstrated that patients following ACLR have knee extensor torque-velocity relationships of the involved limb about half the magnitude of the contralateral limb, using the two-point method, and a lesser slope than the contralateral limb using multiple velocity characterization. The torque-velocity relationship may identify persistent deficits not captured by single-velocity testing and can be used to monitor recovery over time.