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Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Aerobic Exercise Training Increases Skeletal Muscle Protein Turnover in Healthy Adults at Rest^1,2

Matthew A. Pikosky^*, Patricia C. Gaine^*, William F. Martin^*, Kimberly C. Grabarz^*, Arny A. Ferrando, Robert R. Wolfe and Nancy R. Rodriguez^*,3

^* Department Nutritional Sciences, University of Connecticut, Storrs, CT and Department of Surgery, University of Texas Medical Branch, Galveston, TX

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

The effect of a 4-wk aerobic exercise training program (30–45 min, 3–5 d/wk, 65% maximal heart rate) on mixed skeletal muscle protein fractional synthetic rate (FSR), fractional breakdown rate (FBR), and net protein balance (FSR – FBR) (NET) was examined in 8 healthy, previously unfit men and women [21.0 ± 0.4 y, 163.7 ± 4.4 cm, 75.6 ± 5.7 kg, 33.5 ± 4.1% body fat, VO_2peak 38.6 ± 2.3 mL/(kg·min)] fed eucaloric diets providing 0.85 g protein/(kg·d) for the 6-wk study. Measurements were made at baseline after 2 wk of diet intervention only, and after 4 wk of aerobic exercise training and diet intervention. Primed continuous infusions of ring-[²H₅]-phenylalanine (2 µmol/kg; 0.05 µmol/(kg·min) and [¹⁵N]-phenylalanine (2 µmol/kg; 0.05 µmol/(kg·min) were used to assess skeletal muscle protein turnover at rest via the precursor-product method. Endurance training improved cardiovascular fitness, with a significant increase in VO_2peak (P < 0.01) and a significant decrease in running time on a standard course (P < 0.01). There were no significant changes in body mass or composition. There was a significant increase in FSR (0.077 ± 0.007 vs. 0.089 ± 0.006%/h, P < 0.05) and decrease in NET (FSR – FBR) (–0.023 ± 0.004 vs. –0.072 ± 0.012%/h, P < 0.05); FBR tended to increase (0.105 ± 0.014 vs. 0.143 ± 0.018%/h; P = 0.06) after training. Findings show that aerobic training for 4 wk increases skeletal muscle protein turnover in previously unfit subjects.

KEY WORDS: • phenylalanine • endurance exercise • skeletal muscle protein turnover

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