Cycling time trial performance is improved by carbohydrate ingestion during exercise regardless of a fed or fasted state

Scand J Med Sci Sports. 2019 May;29(5):651-662. doi: 10.1111/sms.13393. Epub 2019 Feb 17.

Abstract

Purpose: We tested the hypothesis that carbohydrate ingestion during exercise improves time trial (TT) performance and that this carbohydrate-induced improvement is greater when carbohydrates are ingested during exercise in a fasted rather than a fed state.

Methods: Nine males performed 105 minutes of constant-load exercise (50% of the difference between the first and second lactate thresholds), followed by a 10-km cycling TT. Exercise started at 9 am, 3 hours after either breakfast (FED, 824 kcal, 67% carbohydrate) or a 15-hour overnight fast (FAST). Before exercise, after every 15 minutes of exercise and at 5 km of the TT, participants ingested 2 mL kg-1 body mass of a non-caloric sweetened solution containing either carbohydrate (8% of maltodextrin, CHO) or placebo (0% carbohydrate, PLA).

Results: Irrespective of the fasting state, when carbohydrate was ingested during exercise, the rating of perceived exertion (RPE) was lower throughout the constant-load exercise, while the plasma glucose concentration and carbohydrate oxidation were higher during the last stages of the constant-load exercise (P < 0.05). Consequently, TT performance was faster when carbohydrate was ingested during exercise (18.5 ± 0.3 and 18.7 ± 0.4 minutes for the FEDCHO and FASTCHO conditions, respectively) than when the placebo was ingested during exercise (20.2 ± 0.8 and 21.7 ± 1.4 minutes for the FEDPLA and FASTPLA conditions, respectively), regardless of fasting.

Conclusion: These findings indicate that even when breakfast is provided before exercise, carbohydrate ingestion during exercise is still beneficial for exercise performance. However, ingesting carbohydrate during exercise can overcome a lack of breakfast.

Keywords: carbohydrate supplementation; endurance performance; fasting; liver glycogen.

MeSH terms

  • Adult
  • Athletic Performance / physiology*
  • Bicycling / physiology*
  • Blood Glucose / analysis
  • Carbohydrate Metabolism
  • Dietary Carbohydrates / administration & dosage*
  • Double-Blind Method
  • Fasting*
  • Humans
  • Male
  • Physical Exertion
  • Sports Nutritional Physiological Phenomena*
  • Young Adult

Substances

  • Blood Glucose
  • Dietary Carbohydrates