Investigating the effect of Carbohydrate doses on Exogenous Carbohydrate oxidation rates

Cooper-Smith, Natasha (2025). Investigating the effect of Carbohydrate doses on Exogenous Carbohydrate oxidation rates. University of Birmingham. M.Sc.

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Abstract

Carbohydrate supplementation during endurance exercise has been extensively studied, but despite the presence of fueling guidelines, there is insufficient evidence to personalise strategies based on individual factors such as oxidation rates, body size or sex. The potential to personalise carbohydrate intakes based on exogenous carbohydrate oxidation rates has been suggested, but remains unexplored. This thesis aims to evaluate the feasibility of personalising carbohydrate intakes to optimise exogenous oxidation rates during endurance exercise. The primary objective was to assess whether a high, fixed dose of glucose (90 g/h) during exercise could inform individualised carbohydrate strategies by maximising exogenous oxidation. Eleven trained endurance athletes performed three 150-minute cycling trials at 95% of LT1, ingesting either 90g/h or a personalised carbohydrate dose, derived from the first experimental trial; exogenous oxidation rates for each participant were divided by an oxidation efficiency of 80% to identify the rate to provide carbohydrates in the personalised trial. Results indicated that exogenous carbohydrate oxidation rates were comparable between the high-dose and personalised carbohydrate trials. Mean peak exogenous oxidation rates in the personalised trial did not significantly differ from the 90g trial; 0.91 ±0.19 vs 0.91 ±0.15 g/min, respectively; (p =0.847). Heart rate, ratings of perceived exertion, and gastrointestinal fullness were significantly lower in the personalised than the 90g trial, (142 ±12 vs 148 ±13 bpm; 13 ±1 vs 12 ±2; 2.5 ±1.1 vs 1.7 ±1.2 respectively). There were no significant relationships between peak exogenous carbohydrate oxidation and body mass, height, or workload (p ≥0.05) in either the 90g or personalised trial. Plasma glucose and lactate were not significantly different (p =0.812; p =0.360 respectively) between 90g and personalised trials. The low coefficient of variation (19% ±0.3) and limits of agreements between peak and average exogenous CHO oxidation rates across all timepoints in the 90g and personalised trials indicate a consistent response among participants, strengthening the reliability of these findings. Furthermore, total carbohydrate and fat oxidation rates were unaffected by any trial. The second objective examined the reliability of these exogenous carbohydrate oxidation rates across repeated trials; by repeating the initial 90g trial; providing 1.5 g/min of carbohydrates. Mean peak exogenous carbohydrate oxidation rates were not significantly different between the 90g and 90gR trials (0.89 ±0.19 vs 0.96 ±0.21 g/min, respectively; p =0.25). Ratings of perceived exertion, measures of gastrointestinal comfort and heart rate were all not significantly different between the two repeat 90g trials (p =0.393; p >0.05; p =0.900, respectively). In conclusion, it is possible to personalise carbohydrate ingestion rates to optimise exogenous oxidation and improve gut comfort during endurance exercise, supporting the potential for individualised dosing strategies. Additionally, whilst tighter controls are required, the determination of exogenous carbohydrate oxidation is somewhat reliable and research should extend to investigate the effect of multiple carbohydrates to determine whether the observed trends are evident, and therefore more applicable with current CHO recommendations during exercise.

Type of Work:

Thesis (Masters by Research > M.Sc.)

Award Type:

Masters by Research > M.Sc.

Supervisor(s):