M. L. NEWELL¹, G. A. WALLIS², S. D. R. GALLOWAY¹*
*Corresponding Author
1. Health and Exercise Science Research Group, School of Sport, University of Stirling, Stirling, Stirlingshire,FK9 4LA, Scotland, United Kingdom
2. School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom

Abstract

Carbohydrate (CHO) ingestion before and during exercise has consistently been reported to increase endurance exercise capacity/performance but the mechanisms responsible and optimal dose required are still debated. Feeding CHO is believed to spare muscle glycogen, spare liver glycogen, have central neural actions, and peripheral neural effects. A combination of these mechanisms is likely and the nature of the exercise performed is key when interpreting these data. Research on the optimal dose of CHO to improve performance over a range of exercise durations and intensities has been a recent focus. Optimal doses suggested from these studies cover a range (30-80 g•h-1) that likely reflects exercise task, training status, and/or individual variation in response.

INTRODUCTION AND HISTORICAL BACKGROUND

After almost 100 years of research on CHO metabolism and exercise there are still big questions over mechanisms of action and optimal dose during exercise to maximise performance (1, 2). The purpose of the present review is to highlight these questions and cover key elements for consideration in future research and for applied sport nutrition practice. To achieve this we consider the historical background, effects of CHO on exercise performance/capacity, mechanisms of action, carbohydrate dose, and practical recommendations.
Dietary carbohydrates (CHO) were first recognised as an important fuel for muscle during moderate to high intensity exercise (defined for the purpose of the review as 50 – 90% of maximal aerobic capacity) by Krogh and Lindhard (3). They observed that participants felt tired and exercise capacity was reduced following a short term high fat diet. However, three days of a high CHO diet reversed these symptoms of fatigue (3). In addition, other authors reported that blood glucose concentration was lower in the majority of competitors immediately following the 1924 Boston Marathon (4, 5). ...