Carbohydrate dose influences liver and muscle glycogen oxidation and performance during prolonged exercise

This study investigated the effect of carbohydrate (CHO) dose and composition on fuel selection during exercise, specifically exogenous and endogenous (liver and muscle) CHO oxidation. Ten trained males cycled in a double‐blind randomized order on 5 occasions at 77% V˙O2max for 2 h, followed by a 30‐min time‐trial (TT) while ingesting either 60 g·h−1 (LG) or 75 g·h−1 13C‐glucose (HG), 90 g·h−1 (LGF) or 112.5 g·h−1 13C‐glucose‐13C‐fructose ([2:1] HGF) or placebo. CHO doses met or exceed reported intestinal transporter saturation for glucose and fructose. Indirect calorimetry and stable mass isotope [13C] tracer techniques were utilized to determine fuel use. TT performance was 93% “likely/probable” to be improved with LGF compared with the other CHO doses. Exogenous CHO oxidation was higher for LGF and HGF compared with LG and HG (ES > 1.34, P 0.90, P = 0.024–0.17). In conclusion, there was no linear dose response for CHO ingestion, with 90 g·h−1 of glucose‐fructose being optimal in terms of TT performance and fuel selection. This study investigated the effect of carbohydrate (CHO) dose and composition (60 and 75 g·h−1 of glucose, and 90 and 112.5 g·h−1 of glucose‐fructose [2:1 ratio]) on fuel selection during exercise, specifically exogenous and endogenous (liver and muscle) CHO oxidation. A 13C stable mass isotope tracer technique was used to determine fuel source utilization in Ten trained males who cycled on 5 occasions at 77% V˙O2max for 2 h, followed by a 30‐min time‐trial (TT). There was no linear dose response for CHO ingestion, with 90 g·h−1 of glucose‐fructose being optimal in terms of TT performance and fuel selection.