Different Carbohydrate Ingestion Patterns Do Not Affect Physiological Responses, Whole-Body Substrate Oxidation or Gastrointestinal Comfort in Cycling

Abstract

Fuelling during endurance exercise has evolved towards greater amounts of carbohydrates (CHO) ingested per hour, which can prove challenging for athletes. However, the effects of different CHO ingestion patterns during exercise have scarcely been investigated in cycling. 20 recreationally active males cycled for 180 min at lactate threshold on two occasions in a randomised counterbalanced order. Participants consumed 90 g/h of CHO, either as 22.5 g every 15 min or 45 g every 30 min (CHO-15 and CHO-30, respectively). Respiratory gases, blood glucose, lactate, heart rate, RPE and gastrointestinal symptoms were assessed every 15 min. Physiological responses showed no difference between conditions or significant interactions, except for blood glucose which saw a greater increase in CHO-15 during the first 30 min (interaction; p = 0.03). Whole body CHO and fat oxidation were not different between conditions (2.38 ± 0.37 and 2.33 ± 0.39 g/min, p = 0.25 and 0.19 ± 0.07 vs. 0.22 ± 0.08 g/min, p = 0.10 for CHO-15 and CHO-30, respectively). Subjective markers of gastrointestinal symptoms did not differ between conditions (p > 0.05) except for urge to defecate (p = 0.05); however, only 1 participant reported a score > 4 across any symptoms. Ingesting a larger CHO amount at less regular intervals during prolonged cycling had minimal impact on physiological responses to exercise, whole-body substrate oxidation and gut discomfort, allowing athletes to freely select their preferred strategy.

Keywords: endurance exercise; exercise metabolism; performance; sport nutrition.

FIGURE 1

Schematic of study protocol for each condition, where participants followed a standardised high CHO diet for 24 h prior to completing a 180 min steady state cycling protocol followed by an exercise capacity test. CHO, carbohydrates; g/kg, grams per kilogramme of body mass; LT1, lactate threshold 1; PRO, protein; TTE, time to exhaustion.

FIGURE 2

Plasma glucose (a) and lactate (b) concentration during 180 min steady state cycling with high CHO availability through different CHO ingestion patterns of 22.5 g CHO every 15 min (CHO‐15) or 45 g CHO every 30 min (CHO‐30). Data presented as means ± SD. ^a Significantly different from first timepoint. ^†Significant interaction, where conditions responded differently at the 30 min time point.

FIGURE 3

Carbohydrate oxidation (a), fat oxidation (b) and respiratory exchange ratio (c) throughout 180 min steady state cycling with high carbohydrate availability through different carbohydrate ingestion pattern. ^a Significantly different from CHO‐15.

FIGURE 4

Total carbohydrate (a) and fat utilisation (b) with individual data points, during 180 min steady state cycling with high carbohydrate availability through different carbohydrate ingestion patterns. * Indicates significant difference between conditions (p = 0.04).