Carbohydrate supplementation during prolonged cycling exercise spares muscle glycogen but does not affect intramyocellular lipid use |
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Authors: | Trent Stellingwerff Hanneke Boon Annemie P Gijsen Jos H C H Stegen Harm Kuipers Luc J C van Loon |
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Institution: | (1) Department of Movement Sciences, Nutrition Research Institute Maastricht (NUTRIM), Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands;(2) Department of Human Biology, Nutrition Research Institute Maastricht (NUTRIM), Maastricht University, Maastricht, The Netherlands |
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Abstract: | Using contemporary stable-isotope methodology and fluorescence microscopy, we assessed the impact of carbohydrate supplementation
on whole-body and fiber-type-specific intramyocellular triacylglycerol (IMTG) and glycogen use during prolonged endurance
exercise. Ten endurance-trained male subjects were studied twice during 3 h of cycling at 63 ± 4% of maximal O2 uptake with either glucose ingestion (CHO trial; 0.7 g CHO kg−1 h−1) or without (CON placebo trial; water only). Continuous infusions with U-13C] palmitate and 6,6-2H2] glucose were applied to quantify plasma free fatty acids (FFA) and glucose oxidation rates and to estimate intramyocellular
lipid and glycogen use. Before and after exercise, muscle biopsy samples were taken to quantify fiber-type-specific IMTG and
glycogen content. Plasma glucose rate of appearance (R
a) and carbohydrate oxidation rates were substantially greater in the CHO vs CON trial. Carbohydrate supplementation resulted
in a lower muscle glycogen use during the first hour of exercise in the CHO vs CON trial, resulting in a 38 ± 19 and 57 ± 22%
decreased utilization in type I and II muscle-fiber glycogen content, respectively. In the CHO trial, both plasma FFA R
a and subsequent plasma FFA concentrations were lower, resulting in a 34 ± 12% reduction in plasma FFA oxidation rates during
exercise (P < 0.05). Carbohydrate intake did not augment IMTG utilization, as fluorescence microscopy revealed a 76 ± 21 and 78 ± 22%
reduction in type I muscle-fiber lipid content in the CHO and CON trial, respectively. We conclude that carbohydrate supplementation
during prolonged cycling exercise does not modulate IMTG use but spares muscle glycogen use during the initial stages of exercise
in endurance-trained men. |
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Keywords: | Fat metabolism Intramyocellular triacylglycerol IMTG Glycogen Sports drinks Isotopes Exercise |
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