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

Jan 16, 2018Physiological reports

Carbohydrate amount affects how the liver and muscles use stored energy and exercise performance during long workouts

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Abstract

TT performance was 93% "likely/probable" to be improved with 90 g·h of glucose-fructose ingestion compared to other CHO doses.

Exogenous carbohydrate oxidation was higher for glucose-fructose (LGF and HGF) than for glucose alone (LG and HG).
The relative contribution of carbohydrate oxidation from LGF (24.5 ± 5.3%) was moderately higher than from HGF (20.6 ± 6.2%).
Increasing carbohydrate dose beyond intestinal saturation led to higher absolute (29.2 ± 28.6 g·h) and relative muscle glycogen utilization (9.2 ± 6.9%) with glucose-fructose ingestion.
Absolute muscle glycogen oxidation was moderately higher for the high glucose condition (HG) compared to the low glucose condition (LG).
Total fat oxidation was suppressed in the high glucose-fructose condition (HGF) compared to all other carbohydrate conditions.

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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(LG) or 75 g·hC-glucose (HG), 90 g·h(LGF) or 112.5 g·hC-glucose-C-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 [C] 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 < 0.01), with the relative contribution of LGF (24.5 ± 5.3%) moderately higher than HGF (20.6 ± 6.2%, ES = 0.68). Increasing CHO dose beyond intestinal saturation increased absolute (29.2 ± 28.6 g·h, ES = 1.28, P = 0.06) and relative muscle glycogen utilization (9.2 ± 6.9%, ES = 1.68, P = 0.014) for glucose-fructose ingestion. Absolute muscle glycogen oxidation between LG and HG was not significantly different, but was moderately higher for HG (ES = 0.60). Liver glycogen oxidation was not significantly different between conditions, but absolute and relative contributions were moderately attenuated for LGF (19.3 ± 9.4 g·h, 6.8 ± 3.1%) compared with HGF (30.5 ± 17.7 g·h, 10.1 ± 4.0%, ES = 0.79 & 0.98). Total fat oxidation was suppressed in HGF compared with all other CHO conditions (ES > 0.90, P = 0.024-0.17). In conclusion, there was no linear dose response for CHO ingestion, with 90 g·hof glucose-fructose being optimal in terms of TT performance and fuel selection. -1 -1 13 -1 -1 13 13 13 -1 -1 -1 -1

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

Abstract

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