Abstract
BackgroundMuscle glycogen has been well established as the primary metabolic energy substrate during physical exercise of moderate- to high-intensity and has accordingly been implicated as a limiting factor when such activity is sustained for a prolonged duration. However, the role of this substrate during repeated exercise after limited recovery is less clear, with ongoing debate regarding how recovery processes can best be supported via nutritional intervention. The aim of this project is to examine the causes of fatigue during repeated exercise bouts via manipulation of glycogen availability through nutritional intervention, thus simultaneously informing aspects of the optimal feeding strategy for recovery from prolonged exercise.Methods/DesignThe project involves two phases with each involving two treatment arms administered in a repeated measures design. For each treatment, participants will be required to exercise to the point of volitional exhaustion on a motorised treadmill at 70% of previously determined maximal oxygen uptake, before a four hour recovery period in which participants will be prescribed solutions providing 1.2 grams of sucrose per kilogram of body mass per hour of recovery (g.kg-1.h-1) relative to either a lower rate of sucrose ingestion (that is, 0.3 g.kg-1. h-1; Phase I) or a moderate dose (that is, 0.8 g.kg-1.h-1) rendered isocaloric via the addition of 0.4 g.kg-1.h-1 whey protein hydrolysate (Phase II); the latter administered in a double blind manner as part of a randomised and counterbalanced design. Muscle biopsies will be sampled at the beginning and end of recovery for determination of muscle glycogen resynthesis rates, with further biopsies taken following a second bout of exhaustive exercise to determine differences in substrate availability relative to the initial sample taken following the first exercise bout.DiscussionPhase I will inform whether a dose–response relationship exists between carbohydrate ingestion rate and muscle glycogen availability and/or the subsequent capacity for physical exercise. Phase II will determine whether such effects are dependent on glycogen availability per se or energy intake, potentially via protein mediated mechanisms.Trial registrationISRCTN87937960.
Highlights
Muscle glycogen has been well established as the primary metabolic energy substrate during physical exercise of moderate- to high-intensity and has been implicated as a limiting factor when such activity is sustained for a prolonged duration
Phase I will inform whether a dose–response relationship exists between carbohydrate ingestion rate and muscle glycogen availability and/or the subsequent capacity for physical exercise
The culmination of the results suggests that increasing the amount of carbohydrate is sufficient to maximise glycogen resynthesis rates and restore endurance capacity more completely [11], some indicate a distinct advantage of protein co-ingestion [16,17,18]
Summary
Muscle glycogen has been well established as the primary metabolic energy substrate during physical exercise of moderate- to high-intensity and has been implicated as a limiting factor when such activity is sustained for a prolonged duration. The role of this substrate during repeated exercise after limited recovery is less clear, with ongoing debate regarding how recovery processes can best be supported via nutritional intervention The aim of this project is to examine the causes of fatigue during repeated exercise bouts via manipulation of glycogen availability through nutritional intervention, simultaneously informing aspects of the optimal feeding strategy for recovery from prolonged exercise. When periods of recovery are limited (≤8 hours), such as various training and competition scenarios, neither of the aforementioned processes can be entirely restored [11] This underpins the importance of identifying nutritional strategies to maximise recovery and restoration of exercise capacity in concurrence with manifestations of fatigue during a repeated exercise bout. While much is known about the amount, type and timing of nutrient intake that can facilitate muscle glycogen storage and/or the capacity for repeated physical exertion [11], little evidence exists to demonstrate a link between these variables
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