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Oxidation of exogenous glucose, sucrose, and maltose during prolonged cycling exercise

Human Performance Laboratory, School of Sport and Exercise Sciences, University of Birmingham, Birmingham B15 2TT, United Kingdom

Submitted 23 September 2003 ; accepted in final form 3 November 2003

The purpose of the present study was to investigate whether combined ingestion of two carbohydrates (CHO) that are absorbed by different intestinal transport mechanisms would lead to exogenous CHO oxidation rates of >1.0 g/min. Nine trained male cyclists (maximal O₂ consumption: 64 ± 2 ml·kg body wt^-1·min^-1) performed four exercise trials, which were randomly assigned and separated by at least 1 wk. Each trial consisted of 150 min of cycling at 50% of maximal power output (60 ± 1% maximal O₂ consumption), while subjects received a solution providing either 1.8 g/min of glucose (Glu), 1.2 g/min of glucose + 0.6 g/min of sucrose (Glu+Suc), 1.2 g/min of glucose + 0.6 g/min of maltose (Glu+Mal), or water. Peak exogenous CHO oxidation rates were significantly higher (P < 0.05) in the Glu+Suc trial (1.25 ± 0.07 g/min) compared with the Glu and Glu+Mal trials (1.06 ± 0.08 and 1.06 ± 0.06 g/min, respectively). No difference was found in (peak) exogenous CHO oxidation rates between Glu and Glu+Mal. These results demonstrate that, when a mixture of glucose and sucrose is ingested at high rates (1.8 g/min) during cycling exercise, exogenous CHO oxidation rates reach peak values of 1.25 g/min.

carbohydrate absorption; stable isotopes; substrate utilization; metabolism; sodium-dependent glucose transporter 1; cyclists

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