REF-978 · Cox et al., 2010 · Journal of Applied Physiology, Vol. · Paper · PubMed

Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling

Blimited evidenceMeasured on trained to highly trained athletesWritten before October 2026, being re-checked

Sixteen endurance-trained cyclists or triathletes were pair matched and randomly allocated for 28 days to a high-carbohydrate group, given carbohydrate during daily training, or an energy-matched low-carbohydrate group, in which it was withheld.

Before and at the end, each completed 100 min of steady-state cycling followed by a 7-kJ/kg time trial, once with water and once with a 10% glucose solution. In the High group, tracer-derived exogenous glucose oxidation during the steady-state ride rose from 54.6 to 63.6 g, with no change in the Low group.

Cycling performance improved by approximately 6% after training, and the authors conclude that the metabolic differences between diets did not alter the size of that improvement.

Participants

n=16 endurance-trained cyclists or triathletes, pair matched and randomly allocated: High group n = 8, Low group n = 8. Sex, age and fitness are not given in the abstract.

Protocol

Intervention: 28 days of training with daily carbohydrate intake varied by providing (High) or withholding (Low) carbohydrate during daily training; the Low diet was energy-matched.
Testing: a 5-day test block immediately before the study and during the final 5 days. In each block the exercise trial — 100 min of steady-state cycling (100SS) followed by a 7-kJ/kg time trial — was completed on two occasions separated by 72 h.
Drinks in the trials: water or a 10% glucose solution throughout the exercise trial, in a counterbalanced design.
Measures: whole-body substrate oxidation throughout 100SS, tracer-derived exogenous glucose oxidation, selected mitochondrial enzymes from a vastus lateralis biopsy, time-trial performance.

Key Results

Exogenous glucose oxidation during 100SS (glucose trial): 54.6 to 63.6 g (P < 0.01) in the High group; no change in the Low group.
Maximal citrate synthase activity rose markedly in the High group: 27 vs. 34 micromol/g/min (P < 0.001).
Cycling performance improved by approximately 6% after training; the authors state that the metabolic changes "do not alter the training-induced magnitude of increase in exercise performance".

Practical Application

"Does taking carbohydrate in training make my body better at using it in a race?" In 16 trained cyclists and triathletes randomised for 28 days, those given carbohydrate during daily training burned more of a glucose drink afterwards (54.6 to 63.6 g over 100 min) while the low-carbohydrate group did not change — but both improved the time trial by approximately 6%. The adaptation is real; a performance advantage was not shown.
What it supports: fuelling daily training is a way to raise the use of a race drink. What it does not support: a promise of a faster race from it, or any claim about symptoms — none were measured.
Inference, not tested here: more oxidation of the same drink implies more of it was absorbed, which is the usual reading of this study as "gut training"; the abstract reports oxidation only.
Not from this paper: the trials with symptom outcomes are REF-979 and REF-980; the working ramp for grams per hour is SYNTH-02; what to change when symptoms appear is SYNTH-08.

Limitations

n=16, 8 per group; a single 28-day block.
No gut outcome: symptoms, gastric emptying and absorption were not measured; the "gut" interpretation is an inference from tracer oxidation.
One drink (10% glucose); no glucose-fructose blend was tested.
The abstract does not give the grams of carbohydrate taken in training, the sex of the participants or the time-trial results per group.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

parallel RCT, n=16 (8 per group)