Abstract P302: Energy Expenditure Responses to Exercise Training in Older Women: The Influence of Baseline Physical Activity

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Introduction: Components of energy expenditure are not static. There is debate over whether there is a reduction in non-exercise activity thermogenesis (NEAT) that compensates for energy cost of exercise training. The purpose of this study was to determine the changes in components of energy expenditure following exercise training, and whether any of the changes differ by dose of exercise. Methods: Older inactive women (60-75 years, less than 20 minutes of structured exercise for 3 times/week, n=72) participated in 4 months of exercise training of lower- or higher-dose (8 and 14 kcal/kg body weight weekly, respectively). The exercise was treadmill walking, 3 to 4 times per week, at 50-55% of heart rate reserve. Total daily energy expenditure (TDEE) by the doubly labeled water method, resting metabolic rate (RMR) via indirect calorimetry, and total physical activity by ActiGraph accelerometers (counts per minute), were measured at baseline and in the last two weeks of exercise training. Exercise energy cost was determined by speed, slope, and duration of walking according to the American College of Sports Medicine guideline. NEAT was calculated as (TDEE x 0.9 – RMR – exercise energy cost). Results: There were no group differences in the changes in energy expenditure measures (p for time x group interaction > 0.10 for all). TDEE, RMR, NEAT and total physical activity did not change at the end of exercise training (p > 0.05 for all). However, a significant baseline physical activity x time interaction was found for several energy expenditure measures. Data were therefore stratified into tertiles based on baseline physical activity. In the highest tertile, TDEE remained unchanged but NEAT and total physical activity decreased (p < 0.05 for all). In contrast, in the mid- and lowest tertiles, NEAT remained unchanged, total physical activity increased, and TDEE was unchanged or increased (p < 0.05 for all). Conclusions: In this group of older women, 4 months of aerobic exercise training did not change any of the energy expenditure measures in the overall sample. However, baseline physical activity levels influenced the energy expenditure responses, indicating reductions in NEAT and total physical activity despite participation in exercise training in those who had higher physical activity level at baseline.