The Impact of Focal Mechanical Vibration on Muscle Morphology: A Proof of Concept Study Using Ultrasound Imaging with Shear Wave Elastography

Suwanee, GA

INTRODUCTION: Focal mechanical vibration (FMV) uses mechanical vibration to stimulate specific muscles or areas of the body. The reported benefits include increased muscle strength, decreased pain, improved range of motion (ROM), and enhanced muscle coordination. When FMV is applied, it stimulates muscle fibers and sensory receptors in the muscle and tendon, which facilitates cyclical rapid muscle contraction and relaxation. When the muscle spindle is stimulated, a vibratory-induced inhibition can occur, which is frequency and amplitude-dependent, causing a reduction in muscle activity which may lead to improvements in joint mobility. Consequently, applying FMV to specific muscles increases the elasticity via contraction through autogenic inhibition, thus improving the overall range of motion (ROM). There is some evidence that FMV can improve hamstring muscle flexibility; however, its impact on muscle morphology is poorly understood. Ultrasound with shear wave elastography (US-SWE) is an emerging technology that may contribute to understanding the mechanism of action associated with FMV. The technology quantifies the stiffness or elasticity of soft tissue by measuring the propagation speed of ultrasound-induced shear waves within the tissue. The speed of the wave is directly related to the stiffness of the tissue. Since muscle stiffness increases with contraction and decreases with relaxation, US-SWE can be used to quantify the impact of FMV on muscle.

OBJECTIVE: The purpose of this study is to determine what muscle morphological changes occur on the hamstring musculature following the application of FMV via a device called VibraCool and if a self-reported perception of hamstring muscle tightness is associated with these changes.

METHODS: The PCOM institutional review board approved this study, and all participants provided informed consent. A convenience sample of 10 individuals were recruited. Baseline assessment required participants to self-report their perceived hamstring muscle tightness via a Likert scale and perform the sit-and-reach test and straight leg raise (SLR) for ROM assessment of hamstring muscle length. An Aixplorer ultrasound scanner with US-SWE and a linear transducer were used to acquire all images while the participant lay prone to determine muscle stiffness. Shear wave color maps were acquired at the maximum ROM attained during the SLR for the hamstring (semimembranosus and semitendinosus) muscles and in the prone position. The transducer placement was marked on the skin with a permanent marker to ensure the same regions of interest were imaged post-FMV application. Focal mechanical vibration was then applied to the hamstring muscles via a Vibracool device that delivers constant vibration of 225Hz with an intensity of 7.9 g’s. for 20 minutes with participants in the prone position. All baseline assessments were then repeated post-FMV. Three US-SWE images were acquired at each location, with the mean used for analysis.

RESULTS: Descriptive statistics will be reported, and a repeated measures ANOVA will be completed to determine whether there is a statistically significant difference between the means with a level of significance set at p=.05 A Bonferroni correction will be used if an interaction effect is noted.

CONCLUSION: TBD