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Carbohydrate intake and metabolism during prolonged endurance exercise

Pfeiffer, Beate (2010)
Ph.D. thesis, University of Birmingham.

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It is well accepted that CHO ingestion can improve endurance performance. However, a number of questions remain open regarding fine-tuning CHO intake recommendations during prolonged endurance events. A way to measure the bioavailability of ingested CHO is to measure exogenous CHO oxidation with the use of \(^{13}\)C or \(^{14}\)C tracers. This, however, has been studied only with CHO solutions, predominantly during cycling. In this thesis, we demonstrated that glucose+fructose ingested in the form of gel (1.8 g/min) is as effectively oxidized as an isocarbohydrate solution (1.44±0.29 g/min vs 1.42±0.23 g/min, respectively). Accordingly, the ingestion of glucose+fructose in a solid bar (1.55 g CHO/min) was demonstrated to be oxidized at high rates (1.25±0.15 g/min), comparable to a solution (1.34±0.27 g/min). A comparison of CHO ingestion (1.5 g/min) during cycling and running at the same relative, moderate-intensity (~60% exercise-specific VO\(_2\)max) resulted in similar exogenous CHO oxidation rates (1.25±0.10 g/min vs 1.19±0.08 g/min, respectively). The present thesis also tested the gastrointestinal (GI) tolerance of high CHO ingestion rates (1.4 g CHO/min), previously recommended to athletes. High intakes in the form of a glucose+fructose gel were, on average, well tolerated during a 16-km run, and there was no difference between tolerance of glucose and glucose+fructose gel. A questionnaire-based field study of 221 athletes during prolonged endurance events (running, cycling and triathlon) revealed that voluntary CHO intake rates vary greatly between events and individuals (6-136 g/h). High CHO intakes were related to increased scores for nausea and flatulence as well as to better performance. GI distress during all studies was correlated with a reported history of GI distress. Findings from those studies suggest a need for more individualized nutritional advice that optimizes CHO and fluid delivery to enhance performance, while minimizing GI discomfort

Type of Work:Ph.D. thesis.
Supervisor(s):Jeukendrup, Asker
School/Faculty:Colleges (2008 onwards) > College of Life & Environmental Sciences
Department:The School of Sport and Exercise Sciences
Subjects:QP Physiology
Institution:University of Birmingham
ID Code:1091
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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