Effects of 8 months of twice-weekly high versus low intensity whole body vibration on risk factors for hip fracture in postmenopausal women: A randomized controlled trial

Abstract

INTRODUCTION Whole body vibration (WBV) may improve bone mass and reduce fall risk in postmenopausal women at risk of hip fracture, however, the minimum effective dose and relative efficacy of high versus low intensity vibration, are unknown. METHODS Forty-seven postmenopausal women were randomised to control, low intensity (LV) or high intensity (HV) vibration. At baseline and follow-up, biometrics, whole body, proximal femur (PF), lumbar spine (LS) and forearm bone mineral content (BMC), bone mineral density (BMD), LS area, FN area, cortical width, index of bone strength, cross sectional moment of inertia (XR36, Norland), calcaneal broadband ultrasound attenuation (BUA) (QUS-2, Quidel), and functional muscle (chair rise, wall squat) and balance (single leg stance, tandem walk) performance were tested. Dietary calcium was determined via questionnaire and FoodWorks analysis (2007, Xyris, Brisbane). Current and historical bone-relevant physical activity was determined using the BPAQ (1). Treatment groups attended supervised WBV sessions twice weekly for 8 months (LV - 1 x 15 minute session at 30Hz, 0.2g; HV - 2 x 3 minute sessions at 12.5 Hz, ~1g). Treatment effects were examined by repeated measures ANOVA and multiple regression analyses controlling for age, weight, height, calcium consumption and physical activity. RESULTS No significant between-group effects were found for any measure, however, trends were evident and within group effects were observed. Significant bone loss occurred at the hip and spine in control (p=0.02) but not WBV groups. Wall squat time ("muscle strength/endurance") and single leg stance ("static balance") improved in the HV group (p=0.004) and a similar trend was evident for the LV group but not controls. A significant difference in calcaneal ultrasound between control and HV groups at baseline disappeared at follow-up as a result of bone loss in controls and gain in the HV group. CONCLUSIONS Findings suggest that twice-weekly WBV cannot entirely prevent age-related skeletal loss, but that loss may be considerably muted. Muscle and balance function can be improved with very minimal exposure to high intensity WBV. Findings have important clinical implications for groups at high risk of hip fracture who are unable or unwilling to adopt traditional therapeutic options. 1 Weeks BK and Beck BR: The BPAQ: A bone-specific physical activity assessment instrument. Osteoporosis International, 19(11):1567-1577, 2008.