Effect of Bone on Vibration-Induced Muscle Strength Gain

Overview

The aim of this study is to investigate whether there is a relation between bone mineral density of lower limbs exposed to vibration and the muscle strength gain in the knee extensors and flexors, and a relation serum sclerostin level and the muscle strength gain in the knee extensors and flexors in healthy young adult women. Forty healthy young adult women are planned to include in this study. The participants meeting the criteria were randomized into two groups: the training group (20 cases) and the Control group (20 cases). The whole-body vibration (WBV) training group will be trained on a WBV platform (Power Plate) 5 times a week for 4 weeks period. Participants will be asked to stand upright on WBV platform. Training volume and training intensity will be low at the beginning but progressed slowly according to the overload principle. The training volume will be increased systematically over the 4-week training period. The training intensity will be increased by increasing the amplitude (2-4 mm) and the frequency (40 Hz) of the vibration. The subjects will be asked to report negative side effects or adverse reactions in their training diary. In the Control group, sham stimulus will be performed by WBV platform 5 times a week for a 4 weeks period. Plasma sclerostin level and, the right and left knee flexor and extensor muscles strength will be measured before and after training period. Isokinetic torque will be measured with the Biodex (Biodex System 3 PRO Multijoint System Biodex Medical Inc. Shirley/NY USA)extremity-testing system. The right and left lower limbs bone mineral density (BMD) and muscle strength will be measured before training period. The BMD will be evaluated by bone densitometer (Norland XR-46 DXA, USA). Sclerostin levels will be measured by human sclerostin ELISA kit. The rest muscle electrical activity of right and left knee flexor and extensor muscles will be evaluated at pre-vibration, post- vibration and, during vibration. The rest muscle electrical activity will be measured by Powerlab (data acquisition system, ADInstruments, Australia) device.

Vibration has a strong osteogenic effect. Vibration-induced bone formation is neuronally regulated. Vibration can also effectively enhance muscle strength and power. Previous studies have shown that vibration increases muscle electromyographic (EMG) activity. Attempts to explain vibration-induced increases in EMG activity were based on the tonic vibration reflex. Tonic vibration reflex activates the muscle spindles, thereby enhancing the excitatory drive reflex of the alpha motoneurons. On the contrary, it was shown that the vibration treatment did not enhance the muscle spindle sensitivity and led to presynaptic inhibition of muscle spindle group Ia afferents. As an alternative to tonic vibration reflex, the recently described bone myoregulation reflex has been suggested to potentially explain the increased muscle strength and electrical activity induced by vibration. Based on the bone myoregulation reflex, bone is sensitive to mechanical stimuli and can send mechanical input signals to central nervous system and so can neuronally regulate the muscle activity. The cyclic mechanical loading to the bone stimulates the osteocytes. According to bone myoregulation reflex, the more the osteocytes are stimulated by the cyclic mechanical loading, the increase occurring in the muscle strength and activity may be more. The rate of osteocytes stimulated by vibration may be determined with serum sclerostin level. Sclerostin, the protein product of the SOST gene, is an osteocyte-specific cysteine knot-secreted glycoprotein that is a potent inhibitor of bone formation. Sost/sclerostin levels have been reported to be reduced by mechanical stimulation.