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Carbohydrate Feeding During Prolonged Cycling Exercise Improves Exercise Capacity but Does Not Alter Muscle Fuel Selection

Fell, J (2021) Carbohydrate Feeding During Prolonged Cycling Exercise Improves Exercise Capacity but Does Not Alter Muscle Fuel Selection. Doctoral thesis, Liverpool John Moores University.

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Abstract

The aim of this thesis was to determine the dose-response relationship of CHO feeding during exercise on muscle fuel selection and exercise capacity under conditions considered best nutritional practice. Study 1 demonstrated that after a 36 h CHO loading protocol and high CHO pre-exercise meal, trained male cyclists are capable of completing 180-min of submaximal exercise at lactate threshold (LT) and that fatigue during the subsequent exercise capacity test typically occurred within <10 minutes. However, important methodological considerations from this exercise protocol suggest that at least one full familiarisation of the complete exercise protocol should be included in subsequent studies. Study 2 and 3, utilising this protocol, reported that in conditions of high pre-exercise CHO availability (similar to Study 1), CHO feeding (comprising a mixture of solids, gels and fluids) during exercise improves cycling exercise capacity in a dose dependent manner such that 90 g·h-1 > 45 g·h-1 > 0 g·h-1 CHO. Such ergogenic effects were found to be independent of whole muscle glycogen, fibre-specific glycogen and intramuscular triglyceride (IMTG) sparing and in turn were suggested to be due to a combination of liver glycogen sparing, increased plasma glucose availability and greater maintenance of CHO oxidation. In addition, we report for the first time that 180-min of submaximal exercise reduces IMTG content in both the central and peripheral regions of type I and IIa fibres independent of CHO feeding and this was reflective of decreased LD number in both fibre types whereas reductions in LD size was exclusive to type I fibres. Study 4 aimed to subsequently quantify muscle glycogen utilisation in specific subcellular storage pools, as measured using transmission electron microscopy. However, due to the associated laboratory restrictions of the COVID-19 world pandemic, it was not possible to complete this analysis. Having assessed the effects of CHO feeding on fuel selection and exercise capacity in the laboratory setting, Study 5 used a case-study design to demonstrate the practical delivery of a periodised approach to CHO feeding for a professional World Tour cyclist during a Grand Tour. This approach was successful in supporting a winning performance and provides the first report in the literature to document the practical application of such a periodised approach in professional cycling. In summary, given that Grand Tours in professional road cycling can be won or lost with a matter of seconds, the findings within this thesis are of practical significance for road cyclists in that the chosen CHO strategy may improve the capacity to “hold a wheel” or “mount attacks” during the closing periods of race defining mountain stages.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Exercise; carbohydrate; metabolism; performance; glycogen; intramuscular triglycerides
Subjects: R Medicine > RC Internal medicine > RC1200 Sports Medicine
Divisions: Sport & Exercise Sciences
Date Deposited: 08 Feb 2021 09:32
Last Modified: 08 Feb 2021 09:33
DOI or Identification number: 10.24377/LJMU.t.00014404
Supervisors: Morton, J, Shepherd, S and Louis, J
URI: https://researchonline.ljmu.ac.uk/id/eprint/14404

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