A Randomized Trial on the Effect of Bone Tissue on Vibration-induced Muscle Strength Gain and Vibration-induced Reflex Muscle Activity

Abstract

Background:Whole-body vibration (WBV) induces reflex muscle activity and leads to increased muscle strength. However, little is known about the physiological mechanisms underlying the effects of whole-body vibration on muscular performance. Tonic vibration reflex is the most commonly cited mechanism to explain the effects of whole-body vibration on muscular performance, although there is no conclusive evidence that tonic vibration reflex occurs. The bone myoregulation reflex is another neurological mechanism used to ex-plain the effects of vibration on muscular performance. Bone myor-egulation reflex is defined as a reflex mechanism in which osteocytes exposed to cyclic mechanical loading induce muscle activity. Aims:The aim of this study was to assess whether bone tissue affect-ed vibration-induced reflex muscle activity and vibration-induced muscle strength gain. Study Design:A prospective, randomised, controlled, double-blind, parallel-group clinical trial.Methods:Thirty-four participants were randomised into two groups. High-magnitude whole-body vibration was applied in the exercise group, whereas low-magnitude whole-body vibration exercises were applied in the control group throughout 20 sessions. Hip bone min-eral density, isokinetic muscle strength, and plasma sclerostin levels were measured. The surface electromyography data were processed to obtain the Root Mean Squares, which were normalised by maxi-mal voluntarily contraction. Results:In the exercise group, muscle strength increased in the right and left knee flexors (23.9%, p=0.004 and 27.5%, p<0.0001, respective-ly). However, no significant change was observed in the knee extensormuscle strength. There was no significant change in the knee musclestrength in the control group. The vibration-induced corrected Root Mean Squares of the semitendinosus muscle was decreased by 2.8 times (p=0.005) in the exercise group, whereas there was no change in the control group. Sclerostin index was decreased by 15.2% (p=0.031) in the exercise group and increased by 20.8% (p=0.028) in the control group.A change in the sclerostin index was an important predictor of a changein the vibration-induced normalised Root Mean Square of the semiten-dinosus muscle (R2=0.7, p=0.0001). Femoral neck bone mineral densitywas an important predictor of muscle strength gain (R2=0.26, p=0.035).Conclusion:This study indicates that bone tissue may have an ef-fect on vibration-induced muscle strength gain and vibration-induced reflex muscle activity. Trial registration: ClinicalTrials.gov: NCT01310348.