Effects of weight loss and exercise on trunk muscle composition in older women.

BACKGROUND: Aging and obesity increase the risk for mobility limitations in women. Although trunk muscle composition is important to physical function, the implication of ectopic fat in the trunk muscles with respect to physical fitness and its potential for modification by lifestyle changes is unknown.

METHODS: The effects of a 6-month period of either weight loss (WL) alone or of aerobic exercise (AEX) plus WL (AEX+WL), on trunk body composition, as measured by dual-energy X-ray absorptiometry (DXA) (to measure trunk fat and lean mass) and computed tomography (CT) (to measure the erector spinae, psoas, lateral abdominal, rectus abdominis muscle, and intramuscular fat, and the intramuscular adipose tissue [IMAT] areas) was determined in 65 overweight and obese postmenopausal women (aged 50-76 years).

RESULTS: The area of the erector spinae, psoas, and rectus abdominis muscles declined with age in the women (P<0.05). Both the spinal and abdominal muscle areas were related to the maximal oxygen uptake (VO2max) (P<0.05). Body weight decreased by 8% after both AEX+WL and WL (P<0.001). The VO2max increased by 11% after AEX+WL (P<0.001) but did not change with WL alone (group effect, P<0.001). The DXA-measured trunk fat mass decreased by 16% after AEX+WL (P<0.001) and by 12% after WL (P<0.001). When both groups were combined, the IMAT decreased in all four muscle groups - by 6% in the erector spinae (P<0.01), by 9% in the psoas (P<0.01), by 11% in the lateral abdominals (P<0.001), and by 6% in the rectus abdominis (P<0.05). The loss of fat mass was related to the loss of IMAT of the erector spinae and the lateral abdominals.

CONCLUSIONS: A lifestyle modification of diet-induced WL alone, or with AEX training, results in a significant reduction of the fat infiltration in the abdominal and spinal muscles of the trunk region. Our finding that losses of total body fat predict a reduction in the IMAT of the trunk supports the idea that WL reduces fat depots throughout the body.