THRESHOLD EXERCISE INTENSITY FOR INDUCING FAT LOSS IN MIDDLE-AGED WOMEN

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1882 Aerobic exercise training is known to promote both total and visceral fat loss, but it is not known whether the intensity of training affects the outcome. Since total energy expenditure increases, but fat utilization decreases, as a function of walking speed, we examined in eight middle-aged women (age 47 to 69) the relative role of energy expenditure and lipid utilization during 16 weeks of training at low to moderate exercise intensities. Training consisted of walking 4.8 km/day, five days a week. Women were matched by age, BMI, body fat and fitness level and assigned to exercise at individual intensities above or below their anaerobic threshold (AT) which was determined at the start and after 16 weeks of training. The change in total, abdominal, and thigh fat content was estimated using girth and skinfold measurements at the start and after 16 weeks of training. Preliminary results show that energy expenditure and lipid utilization, estimated from non-steady-state treadmill tests, were not significantly different between the groups. However, walking at intensities below 105% of AT led to body fat gain of 2.4+/−2.5%, and walking between 105 and 115% of AT led to 1.02+/−1.3% body fat loss (t=2.66, p=0.04). In addition, changes in waist and thigh circumferences followed a similar pattern, with slower walkers showing increases, and faster walkers showing decreases, but the results did not attain significance (t=2.371, p=0.6, and t=2.082, p=0.08). These data suggest that approximately 105% of AT is a threshold walking intensity for body fat loss, but neither differential energy expenditure or lipid utilization appear to be the likely cause.