Changes in Quadriceps Rate of Torque Development After Anterior Cruciate Ligament Reconstruction and Association to Single-Leg Hop Distance

Background: Quadriceps neuromuscular function is negatively affected after anterior cruciate ligament reconstruction (ACLR). The specific effect that the ACLR has on the quadriceps femoris rate of force production and its impact on functional recovery is unknown. Hypothesis: The anterior cruciate ligament (ACL) limb would present persistent deficits in the rate of torque development (RTD), when compared with the non-ACL limb before ACLR until 9 months (9M) post-ACLR. Study design: Prospective cohort study. Level of evidence: Level 3. Methods: Twenty-eight participants performed quadriceps maximum voluntary isometric contractions (MVICs) before (PRE), at 5 months (5M) and at 9M after ACLR. Single-leg hop distance was also assessed at 9M. Quadriceps RTD was calculated at 50, 100, and 200 ms after the onset of torque production. Maximum RTD was also calculated. A 2 (limb) x 3 (time) repeated-measures analysis of variance was used for RTD50, RTD100, RTD200, and RTDmax. Linear regressions were used to evaluate the associations of MVIC and RTD values at 5M and 9M with single-leg hop distance at 9M.Results: The ACL limb had lower RTD values at all times compared with the non-ACL limb (P < 0.05). RTD of the ACL limb significantly decreased from PRE to 5M, and then recovered to PRE levels at 9M (P < 0.05). The non-ACL limb displayed no differences from baseline to either 5M or 9M. MVIC and RTD200 at 5M predicted (R-2 = 0.313 and R-2 = 0.262, respectively) single-leg hop distance at 9M, better than the strength and RTD at 9M (R-2 = 0.235 and R-2 = 0.128, respectively). Conclusion: Quadriceps RTD is negatively affected after ACLR, and deficits may persist at the time of return to activity. Strength and RTD during recovery at 5M may predict more than 25% of the variance in single-leg hop distance at 9M, independently; hence, both provide important information to monitor functional recovery post-ACLR. Clinical relevance: RTD should be measured to understand the changes in neuromuscular capacity after ACLR, and rehabilitation strategies that target quick force production, ie, quick muscle activation and functional tasks, should be implemented.