Effects of exercise on body composition and bone mineral density during lactation

Abstract

Bone mineral density (BMD) decreases during lactation, therefore, the purpose was to see if exercise could slow this loss. Women were randomized to either exercise group (EG, n=11) [weight bearing aerobic exercise (3d/wk, 45 min/d) and 3d/wk of resistance exercise (direct force on axial skeleton)] or control group (CG, n=13, no exercise). To date, 11 have completed the 16 wk study (EG n=5, CG n=6). Body composition and BMD were measured by dual x-ray absorptiometry at lumbar spine (LS), hip, and total body. Maximal strength and maximal oxygen consumption (VO2max) were determined by 1 repetition maximum and submaximal treadmill test, respectively. Significant differences in change from baseline between CG and EG were observed for LS bone mineral content (BMC) (−7.4 ± 2.4 vs −2.9 ± 1.0%, p<0.01) and LS BMD (−6.9 ± 1.9 vs −4.6 ± 1.1%, p=0.03), respectively. LS area increased by 1.8 ± 1.2% in the EG vs a decrease of −0.6 ± 2.7% in the CG (p=0.09). No significant differences in percent change were seen in total body BMD and total hip BMD. Maximal strength change increased by 23–166% for all exercises in the EG, whereas, the CG increased by 0–14%, except pushups (90%). VO2max increased in both groups (EG = 9.8 ± 7.8, CG = 6.3 ± 4.6%). Percent weight change was −5.3 ± 3.8 and −4.4 ± 4.4% for the CG and EG, respectively. EG women lost more fat mass (−2.1 ± 2.9 vs −1.5 ± 1.7 kg) and less lean body mass (−1.0 ± 1.2 vs −1.9 ± 0.8 kg), however these changes were not significant. These results suggest that resistance and aerobic exercise slow BMC loss and increase bone area of the LS resulting in less loss of BMD during lactation. Supported by NC Agricultural Research Services