Impact exercise and bone density in premenopausal women with below average bone density for age.

Abstract

To study the effects of two home-based impact exercise programs on areal bone mineral density (aBMD) in adult premenopausal women with below average aBMD for age (negative Z-scores; 40.8years; n=107). Two unilateral impact exercise programs were employed, one targeting the total hip and lumbar spine (n=42 pairs), the other the distal radius (n=24 pairs) with some individuals performing both. Force plate data were used to establish exercise loading characteristics (peak loads, time to peak), dual-energy X-ray absorptiometry (DXA) provided bone data. Calcium intake, health and extraneous physical activity (PA) were determined by survey. Exercise for both hip and spine consisted of unilateral landings from adjustable steps (maximum height 63.5cm) while impacts were delivered to the forearm by arresting falls against a wall. An exercise log was used to provide the exercise prescription, record each exercise bout and any injuries. Participants were randomly assigned to exercise or control groups and pair-matched (age, BMI, Z-score, aBMD). Compliance was calculated as the number of sessions completed divided by the total prescribed number (mean ~50%). The programs delivered significant gains pre to post at each site compared with significant losses in controls (forearm: 3.9 vs -3.9%; total hip: 2.0 vs -2.6%; lumbar spine: 2.8 vs -2.9% exercise and controls, respectively, all p<0.001). No exerciser lost bone at the target site regardless of compliance which was strongly correlated with bone gains (R (2)=0.53-0.68, all p<0.001). Impact exercise provides an effective means of improving below average aBMD without supervision in this at risk population.