Does Frequency Of Resistance Training Effect Proximal Femur Bone Mineral Density In Community-dwelling Senior Women?

Abstract

Longitudinal studies suggest proximal femur areal bone mineral density (aBMD) decreases with age; resistance training (RT) may offset this loss in older women. ACSM recommends older adults engage in RT 2-3 ×/week to maintain bone mass, but few studies investigated the effect of RT frequency on BMD. PURPOSE: To compare the effect of RT frequency (0, 1, or 2 ×/week) on total proximal femur aBMD in post-menopausal women. METHODS: We conducted an a priori secondary analysis of a 12 month randomized controlled trial whose primary outcome was cognitive function. We enrolled 155 community-dwelling women and randomized them to 1 of 3 group-based exercise interventions: (i) twice-weekly RT (RT2); once-weekly RT (RT1); or (iii) twice-weekly control group with balance and tone exercises (BT). Our primary outcome was aBMD (g/cm2) of the left total proximal femur by dual energy X-ray absorptiometry (DXA). We measured participants at baseline, midpoint, and 12 months. We assessed between-group differences for outcomes using ANCOVA. RESULTS: At baseline, 144 women were assessed by DXA; 111 women returned for DXA assessment at both follow-ups (n: BT= 33, RT1= 39, RT2= 39). At baseline, mean age was 69y for both RT1 and RT2 groups and 70y for BT; mean aBMD (g/cm2) for groups was: BT= 0.813± 0.105, RT1= 0.825± 0.125, and RT2= 0.809± 0.134; mean 6 minute walk test (meters) for BT= 532± 77, RT1= 527± 58, and RT2= 512± 103; median Functional Comorbidity Index score was 2 for all groups; and mean Physical Activity Scale for the Elderly (PASE) score for BT= 128± 52, RT1= 117± 60 and RT2= 130± 63. After controlling for baseline aBMD, there were no differences in aBMD or percent change in aBMD between groups at midpoint and final assessment. The greatest percent change in total proximal femur aBMD for all groups occurred between baseline and 6 months (BT= 1.64%, RT1= 1.74%, RT2= 1.33%). There were no significant between group differences in self-reported activity levels (PASE) outside of the interventions at either follow-up. CONCLUSION: Cross-sectional and cohort studies suggest that community-dwelling older women lose approximately 1% of their bone mass annually. Although there were no differences between groups in bone density at the proximal femur, it was maintained in all three groups; further study is needed to elucidate this effect.