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 explain the effects of vibration on muscular performance. Bone myoregulation 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 affected 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 mineral 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 maximal 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, respectively). However, no significant change was observed in the knee extensor muscle strength. There was no significant change in the knee muscle strength 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 change in the vibration-induced normalised Root Mean Square of the semitendinosus muscle (R2=0.7, p=0.0001). Femoral neck bone mineral density was an important predictor of muscle strength gain (R2=0.26, p=0.035).

Conclusion: This study indicates that bone tissue may have an effect on vibration-induced muscle strength gain and vibration-induced reflex muscle activity.

Trial registration: ClinicalTrials.gov: NCT01310348.

Keywords: Bone mineral density; electromyography; muscle training; sclerostin; tonic vibration reflex.

FIG. 1.

Experimental procedures

FIG. 2.

Flow chart of participants considered for inclusion

FIG. 3. a–d.

Posture of the participants and WBV devices used in this study. A side-alternating WBV device used for the CON group generated vibrations by oscillating along the axis (adjustable gravity force: 0.1 – 33 g) (a, b). A synchronous WBV device was used for the EX group; the whole plate oscillated with a linear movement upward and downward (adjustable gravity force: 1.8 – 6.3 g) (c, d)

FIG. 4. a–c.

Frequency spectrograms of SEMG signals recorded during WBV. Unprocessed SEMG signal (a). Filtered SEMG signal and elimination of artifacts (b). Rectified SEMG signals showing a prominent peak at the vibration frequency (40 Hz) due to synchronisation (c)