Abstract

High-frequency mechanical strain seems to stimulate bone strength in animals. In this randomized controlled trial, hip BMD was measured in postmenopausal women after a 24 week whole body vibration(WBV) training program. Vibration training significantly increased BMD of the hip. These findings suggest that WBV training might be useful in the prevention of osteoporosis.

Introduction

High-frequency mechanical strain has been shown to stimulate bone strength in different animal models. However, the effects of vibration exercise on the human skeleton have rarely been studied. Particularly in postmenopausal women-who are most at risk of developing osteoporosis-randomized controlled data on the safety and efficacy of vibration loading are lacking. The aim of this randomized controlled trial was to assess the musculoskeletal effects of high-frequency loading by means of whole body vibration (WBV) in postmenopausal women.

Materials and Methods

Seventy volunteers (age, 58 -74 years) were randomly assigned to a whole body vibration training group (WBV, n25), a resistance training group (RES, n22), or a control group (CON, n23). The WBV group and the RES group trained three times weekly for 24 weeks. The WBV group performed static and dynamic knee-extensor exercises on a vibration platform (35- 40 Hz, 2.28 -5.09g), which mechanically loaded the bone and evoked reflexive muscle contractions. The RES group trained knee extensors by dynamic leg press and leg extension exercises, increasing from low (20 RM) to high (8 RM) resistance. The CON group did not participate in any training. Hip bone density was measured using DXA at baseline and after the 6-month intervention. Isometric and dynamic strength were measured by means of a motor-driven dynamometer. Data were analyzed by means of repeated measures ANOVA. Results: No vibration-related side effects were observed. Vibration training improved isometric and dynamic muscle strength and also significantly increased BMD of the hip. No changes in hip BMD were observed in women participating in resistance training or age-matched controls, respectively; not significant). Serum markers of bone turnover did not change in any of thegroups.

Materials and Methods

Subjects and study design Seventy postmenopausal women volunteered to participate in the study. Assessment of eligibility for participation was based on a screening by questionnaire and a thorough medical examination. Women had to be between 60 and 70 years of age, non institutionalized, and free from diseases or medications known to affect bone metabolism or muscle strength. Subjects with a total body BMD T-score of less than 2.5 (the WHO definition for osteoporosis) were also excluded from this study. All subjects were randomly assigned to one of the study groups using computer-generated random numbers. A total of 25 women were trained for 6 months on a vibrating platform (WBV group). A group of 22 woman participated in a resistance training program (RES group). Both training programs consisted of 72 training sessions within a 24-week period. Training frequency was three times a week, with at least 1 day of rest between two sessions. A group of 23 age-matched women served as a control group (CON group) and did not participate in any training. The baseline characteristics of both groups are indicated in Table 1. All participants gave their informed written consent before enrollment, and the study protocol was approved by the Leuven University Human Ethics Committee. WBV The subjects in the WBV group performed static and dynamic knee-extensor exercises on the vibration platform (Power Plate, Amsterdam. The Netherlands): squat, deep squat, wide stance squat, one-legged squat, and lunge.Training load was low at the beginning but progressed slowly according to the overload principle.

The training

volume increased systematically over the 6-month training period by increasing the duration of one vibration session,

the number of series of one exercise, or the number of

different exercises.

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