ACL Reconstructed Individuals With Poorer Quadriceps Function Demonstrate Greater Acute Improvements Following Vibration

Abstract

Quadriceps dysfunction is common following anterior cruciate ligament reconstruction (ACLR). Whole body (WBV) and local muscle (LMV) vibration improve measures of quadriceps function such as corticomotor excitability, central activation ratio (CAR), peak torque (PT), and rate of torque development (RTD) in those with ACLR. However, it is unknown if baseline quadriceps function influences the response to vibration. PURPOSE: To evaluate relationships between baseline quadriceps function and changes in these measures following WBV and LMV. METHODS: Quadriceps function was assessed in 20 individuals with ACLR (age 21 ± 1 yr; time since ACLR 51 ± 21 mo) prior to and following WBV and LMV administered on separate days. Quadriceps PT, RTD, and CAR were assessed via maximal voluntary isometric contractions (MVIC) during which a supramaximal electrical stimulus was applied. Corticomotor excitability was assessed via the active motor threshold (AMT), motor evoked potential (MEP), and spinal reflexive excitability was assessed via the Hoffmann-reflex (H:M ratio). Six 60s bouts of WBV or LMV (30 Hz, 2 g) were administered while the subject stood in slight knee flexion. Pearson correlations were used to evaluate relationships between baseline values for each measure of quadriceps function and the respective pre-post change scores following WBV. RESULTS: For WBV, lower MEP baseline values were associated with greater MEP change scores (P = 0.02, r = -0.52). No other relationships were significant for WBV (P = 0.19 - 0.88, r = -0.31 - -0.03. For LMV, lower RTD baseline values were associated with greater RTD change scores (P = 0.004, r = -0.61). No other relationships were significant for LMV (P = 0.38 - 0.75, r = -0.21 - 0.12). CONCLUSION: Individuals with lower baseline MEP exhibited greater MEP increases following WBV and those with lower RTD displayed greater RTD increases following LMV. These findings suggest that individuals with ACLR who possess larger deficits in quadriceps function may glean greater benefit from vibration. Quadriceps function is chronically suppressed after ACLR, and vibration may be a viable rehabilitation approach for patients with chronic deficits in quadriceps function. However, ACLR patients in whom quadriceps function is nearly restored may receive limited benefits from this approach.