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Human Nutrition and Metabolism

Aerobic Exercise Training Decreases Leucine Oxidation at Rest in Healthy Adults^1,2

Patricia C. Gaine^*, Christian T. Viesselman^**, Matthew A. Pikosky^*, William F. Martin^*, Lawrence E. Armstrong, Linda S. Pescatello^** and Nancy R. Rodriguez^*,3

Departments of ^* Nutritional Sciences and Kinesiology, and ^** School of Allied Health, University of Connecticut, Storrs, CT 06269

³To whom correspondence should be addressed. E-mail: nancy.rodriguez{at}uconn.edu.

Both exercise and dietary protein intake affect whole-body protein turnover (WBPTO). Few studies have investigated the effect of aerobic exercise training on WBPTO [leucine rate of appearance (Ra), oxidation (Ox), and nonoxidative leucine disposal (NOLD)] in untrained individuals consuming a specified level of protein. This study examined the effect of aerobic exercise training on WBPTO in untrained men and women during a controlled diet intervention providing 0.88 g protein/(kg · d). After a 2-wk adaptation to the study diet, 7 subjects [3 men, 4 women; 76.1 ± 5.8 kg, 164.7 ± 4.4 cm, 30.7 ± 4.5% body fat, 39.1 ± 2.8 VO_2max (maximal oxygen uptake) mL/(kg · min)] participated in 4 wk of aerobic exercise training (running and walking 4–5 times/wk at 65–85% maximal heart rate). WBPTO (determined via constant infusion of 1-[¹³C] leucine), nitrogen balance, and body composition were determined at baseline and after 4 wk of training. Nitrogen balance (–1.0 ± 0.7 vs. 0.9 ± 1.1 g N/24 h, P = 0.03) improved with exercise training, whereas body mass and composition did not change. Leucine Ra did not change, Ox decreased [18 ± 2 to 15 ± 2 µmol/(kg · h), P 0.001], and NOLD tended to increase [128 ± 18 to 151 ± 19 µmol/(kg · h), P = 0.09] in response to training. These data indicate improved protein utilization in response to exercise training in weight-stable subjects. This study emphasizes the importance of dietary control, with specific regard to energy and protein intakes, in the characterization of protein utilization in response to an exercise intervention.

KEY WORDS: • protein turnover • body composition • nitrogen balance

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