Substrate Source Use in Older, Trained Males after Decades of Endurance Training

• DOI: 10.1249/mss.0b013e3181572ace
• Publication Date: 2009-03-05T02:46:01Z
• Authors: HANNEKE BOON; RICHARD A. M. JON...; RENE KOOPMAN; ELLEN E. BLAAK; WIM H. M. SARIS; ANTON J. M. WAGEN...; LUC J. C. VAN LOON
• Keywords: Male; 0301 basic medicine; Aging; 0303 health sciences; Rest; Fatty Acids, Nonesterified; Middle Aged; Lipid Metabolism; 03 medical and health sciences; Cross-Sectional Studies; Physical Fitness; Exercise Test; Physical Endurance; Humans; Energy Metabolism; Muscle, Skeletal; Glycogen

The purpose of this study was to compare substrate source use in older, long-term exercising, endurance-trained males with sedentary controls.[U-C]palmitate and [6,6-H2]glucose tracers were applied to assess plasma free fatty acid (FFA) and glucose oxidation rates, and to estimate muscle- and/or lipoprotein-derived triacylglycerol (TG) and muscle glycogen use. Subjects were 10 long-term exercising, endurance-trained males and 10 sedentary controls (age 57 +/- 1 and 60 +/- 2 yr, respectively). Muscle biopsy samples were collected before and after exercise to assess muscle fiber type-specific intramyocellular lipid and glycogen content.During exercise, plasma palmitate Ra, Rd, and Rox were significantly greater in the trained subjects compared with the controls (Ra: 0.36 +/- 0.02 and 0.25 +/- 0.02; Rd: 0.36 +/- 0.03 and 0.24 +/- 0.02; Rox: 0.31 +/- 0.02 and 0.20 +/- 0.02 mmol.min, respectively, P < 0.01). This resulted in greater plasma FFA and total fat oxidation rates in the trained versus sedentary subjects (P < 0.001). Muscle- and/or lipoprotein-derived TG use contributed 10 +/- 2 and 11 +/- 3% in the trained and control groups, respectively (NS). No significant net changes in muscle fiber lipid content were observed.Older, endurance-trained males oxidize more fat during moderate-intensity exercise than do sedentary controls. This greater total fat oxidation rate is attributed to a higher plasma FFA release, uptake, and oxidation rate. In contrast, intramyocellular triacylglycerol does not seem to represent a major substrate source during 1 h of moderate-intensity exercise in older trained or sedentary men.