Time course of the effects of vibration on quadriceps function in individuals with anterior cruciate ligament reconstruction

Abstract

Quadriceps dysfunction is a common, chronic complication following anterior cruciate ligament reconstruction (ACLR) that contributes to aberrant gait biomechanics and poor joint health. Vibration enhances quadriceps function in individuals with ACLR, but the duration of these effects is unknown. This study evaluated the time course of the effects of whole body vibration (WBV) and local muscle vibration (LMV) on quadriceps function. Twenty-four volunteers with ACLR completed 3 testing sessions during which quadriceps isometric peak torque, rate of torque development, and EMG amplitude were assessed prior to and immediately, 10, 20, 30, 45, and 60 min following a WBV, LMV, or control intervention. WBV and LMV (30 Hz, 2g) were applied during six one-minute bouts. WBV increased peak torque 5–11% relative to baseline and control at all post-intervention time points. LMV increased peak torque 6% relative to baseline at 10 min post-intervention and 4–6% relative to control immediately, 10 min, and 20 min post-intervention. The interventions did not influence EMG amplitudes or rate of torque development. The sustained improvements in quadriceps following vibration, especially WBV, suggest that it could be applied at the beginning of rehabilitation sessions to “prime” the central nervous system, potentially improving the efficacy of ACLR rehabilitative exercise.

Introduction

Quadriceps dysfunction is a common, chronic complication following anterior cruciate ligament injury and surgical reconstruction (ACLR) evidenced by deficits in knee extension strength, EMG activity, voluntary activation capacity, and rate of torque development (Hart et al., 2010, Tengman et al., 2014). This phenomenon contributes to aberrant gait biomechanics and poor patient self-report and joint health outcomes (Lewek et al., 2002, Pietrosimone et al., 2013, Tourville et al., 2014, Zwolski et al., 2015, Blackburn et al., 2016, Pietrosimone et al., 2018). As such, quadriceps dysfunction is hypothesized to be a primary contributor to development of post-traumatic osteoarthritis following ACLR. Additionally, inability to generate knee extension torque influences biomechanical factors linked to secondary ACL injury risk (Paterno et al., 2010, Ward et al., 2018) and quadriceps dysfunction impedes performance on assessments that are commonly used for clinical decision making regarding the ability to return to unrestricted physical activity (Birchmeier et al., 2019). Deficits in quadriceps strength have been reported more than two decades following ACLR (Tengman et al., 2014) suggesting that current rehabilitation methods are ineffective for restoring quadriceps function.

Vibration enhances quadriceps function in multiple populations including healthy controls, stroke patients, healthy individuals with laboratory-induced quadriceps dysfunction (e.g. experimental knee effusion), and individuals with ACLR (Tihanyi et al., 2007, Blackburn et al., 2014, Pamukoff et al., 2014, Pamukoff et al., 2016b, Pamukoff et al., 2016a, Pamukoff et al., 2017). In particular, both whole body vibration (WBV) and local muscle vibration (LMV) improve peak torque, rate of torque development, and corticospinal excitability in individuals with ACLR (Pamukoff et al., 2016b, Pamukoff et al., 2017). WBV and LMV embedded in ACLR rehabilitation improves quadriceps function to a greater extent than rehabilitation alone (Moezy et al., 2008, Fu et al., 2013). Additionally, these modalities appear to mitigate aberrant gait biomechanics (Blackburn et al., in press), thus WBV and LMV may be viable adjunct therapies for improving ACLR rehabilitation and reducing the risk of post-traumatic osteoarthritis.

Vibration enhances central nervous system (CNS) excitability and may, therefore, enhance the efficacy of rehabilitative exercise. Vibration suppresses activity of CNS inhibitory neurons in animals (Bills et al., 2019). Vibration also reduces arthrogenic muscle inhibition and enhances corticospinal excitability in humans (Blackburn et al., 2014, Pamukoff et al., 2016b), both of which are contributors to quadriceps dysfunction following ACLR (Lepley et al., 2014). These findings suggest that applying vibration prior to rehabilitation exercise may “prime” the CNS, potentially making these efforts more effective. Quadriceps function is enhanced following LMV for at least 5 min in healthy individuals (Pamukoff et al., 2014), and WBV improves performance on tasks that heavily rely on quadriceps function (e.g. isometric squat) for up to 15 min (Cormie et al., 2006). However, the duration of these effects in individuals with ACLR is unknown. To determine whether vibration is a viable adjunct therapy for ACLR rehabilitation, it is first necessary to determine the duration of these effects so that optimal rehabilitation protocols can be developed (e.g. how frequently should vibration be applied). Therefore, the purpose of this investigation was to determine the time course of the effects of vibration on quadriceps function in individuals with ACLR. We hypothesized both WBV and LMV would improve quadriceps function for at least 10 min following application.