We examined the effects of carbohydrate (CHO) delivery form on exogenous CHO oxidation, gastrointestinal discomfort, and exercise capacity. In a randomized repeated-measures design [after 24 h of high CHO intake (8 g·kg-1) and preexercise meal (2 g·kg-1)], nine trained males ingested 120 g CHO·h-1 from fluid (DRINK), semisolid gel (GEL), solid jelly chew (CHEW), or a coingestion approach (MIX). Participants cycled for 180 min at 95% lactate threshold, followed by an exercise capacity test (150% lactate threshold). Peak rates of exogenous CHO oxidation (DRINK 1.56 ± 0.16, GEL 1.58 ± 0.13, CHEW 1.59 ± 0.08, MIX 1.66 ± 0.02 g·min-1) and oxidation efficiency (DRINK 72 ± 8%, GEL 72 ± 5%, CHEW 75 ± 5%, MIX, 75 ± 6%) were not different between trials (all P > 0.05). Despite ingesting 120 g·h-1, participants reported minimal symptoms of gastrointestinal distress across all trials. Exercise capacity was also not significantly different (all P > 0.05) between conditions (DRINK 446 ± 350, GEL 529 ± 396, CHEW 596 ± 416, MIX 469 ± 395 s). Data represent the first time that rates of exogenous CHO oxidation (via stable isotope methodology) have been simultaneously assessed with feeding strategies (i.e., preexercise CHO feeding and the different forms and combinations of CHO during exercise) commonly adopted by elite endurance athletes. We conclude that 120 g·h-1 CHO (in a 1:0.8 ratio of maltodextrin or glucose to fructose) is a practically tolerable strategy to promote high CHO availability and oxidation during exercise.NEW & NOTEWORTHY We demonstrate comparable rates of exogenous CHO oxidation from fluid, semisolid, solid, or a combination of sources. Considering the sustained high rates of total and exogenous CHO oxidation and relative lack of gastrointestinal symptoms, consuming 120 g CHO·h-1 appears to be a well-tolerated strategy to promote high CHO availability during exercise. Additionally, this is the first time that rates of exogenous CHO oxidation have been assessed with feeding strategies (e.g., coingestion of multiple CHO forms) typically reported by endurance athletes.
Keywords: fructose; maltodextrin; metabolism; stable isotopes.