Does muscle activation during whole-body vibration induce bone density improvement in postmenopausal women?--A systematic review

Abstract

Whole body vibration training (WBV) stimulates muscles by mechanical vibrations. The resulting muscle activity and bone deformation may provoke an increase in bone density. The aim of this systematic review was to evaluate whether muscle activation and muscle strengthening caused by vibration training has an effect on bone density in postmenopausal women. This systematic review was conducted according to the guidelines of the PRISMA statement for meta-analyses and systematic reviews. The literature search was conducted in several electronic databases (PubMed und CINAHL) and Google Scholar. The literature search was conducted between June 2012 and August 2013. The methodological quality of the included studies was assessed using the Cochrane risk of bias tool by two independent persons. A total of 246 studies was found. In this present analysis three studies with vertical and two studies with side-alternating WBV were included, totalling 368 participants with an age range between 60.7 and 79.6 years. From those 132 participants trained on vertically while 67 participants trained on side-alternating WBV engines. The included study shows a moderate to high risk of bias. The selected frequencies ranged from 12.0 Hz to 40.0 Hz for vertical WBV and 12.5 Hz for side-alternating WBV. The amplitude ranged between 1.7 and 12.0 mm with an acceleration from 0.1 to 10.0 g. This systematic review showed significant influences on the isometric maximal voluntary contraction (IMVC) between 15.1 and 16.5 % and on dynamic maximal strength (DMS) between 7.9 to 16.5 % after vertically WBV (frequencies: 30.0 to 40.0 Hz; 3 sessions per week; 15 minutes per session) and on IMV with 26.6 % (frequency: 12.5 Hz; 3 sessions per week; 15 minutes per session). This increased muscle activity resulted in an improved bone density in the lumbar spine between 0.5 % to 0.7 % and the hip between 0.8 % to 0.9 % in postmenopausal women. These clinically significant findings should be confirmed by a large high-quality randomised controlled trial and reported following the CONSORT Statement guidelines.