Carbohydrate Ingestion During Prolonged Exercise Blunts the Reduction in Power Output at the Moderate-to-Heavy Intensity Transition
Dudley-Rode et al.: n=12 trained cyclists and triathletes (10 males, 2 females; VO2peak 59 ± 5 mL/kg/min; training volume 14 ± 5 h/week) performed an incremental test and a 5-min time trial fresh (PRE) and after 150 min of moderate-intensity cycling with (POSTCHO) and without (POSTCON) carbohydrate ingestion.
Power at the first ventilatory threshold (VT1) fell in both conditions, but fell LESS with carbohydrate (−3 ± 2% vs −6 ± 4%). Carbohydrate = partial protection of the moderate-to-heavy boundary, not complete protection.
Protocol
Within-subject comparison: twelve trained cyclists and triathletes (10 males, 2 females; VO2peak 59 ± 5 mL/kg/min; training volume 14 ± 5 h/week) (from the abstract).
Each performed an incremental test and a 5-min time trial (TT) without prior exercise (PRE), and after 150 min of moderate-intensity cycling with (POSTCHO) and without (POSTCON) carbohydrate ingestion.
Measures: power output at the first ventilatory threshold (VT1), 5-min TT mean power, blood glucose concentration.
Key Results
| Outcome | PRE | POSTCHO (with CHO) | POSTCON (no CHO) | CHO vs no-CHO |
|---|---|---|---|---|
| VT1 power | 229 ± 37 W (n=12) | 225 ± 36 W, ∆ −3 ± 2%, P = 0.027 (n=11) | 216 ± 35 W, ∆ −6 ± 4%, P = 0.001 (n=12) | POSTCON lower than POSTCHO: ∆ −7 ± 9 W, −3 ± 4%, P = 0.019 |
| 5-min TT mean power | 363 ± 55 W | 351 ± 53 W, ∆ −4 ± 3%, P = 0.025 | 328 ± 63 W, ∆ −10 ± 10%, P = 0.027 | not significantly different: ∆ 25 ± 37 W, 9 ± 13%, P = 0.186 |
| Blood glucose | — | maintained | significantly lower at 120 and 150 min (P < 0.05) | — |
Mechanisms
Measured: blood glucose was maintained with carbohydrate and had fallen by 120-150 min without it.
Inference, not tested: carbohydrate intake spares muscle glycogen and delays additional motor-unit recruitment, keeping the moderate-heavy boundary higher.
Inference, not tested: maintained blood glucose keeps the CNS fuelled and delays central fatigue.
CHO ≠ complete protection: VT1 still declined with carbohydrate (−3%), but less than without (−6%).
Practical Application
Carbohydrate during a long ride protects the moderate-heavy boundary: in 12 trained cyclists/triathletes, VT1 power after 150 min of moderate riding fell −3 ± 2% with carbohydrate vs −6 ± 4% without (P = 0.019 between conditions). The trial compared carbohydrate against none, and identifies no dose, no timing and no product.
Do not expect fuelling to protect a hard finish by itself: the 5-min time trial after the preload fell in both conditions (−4% with CHO, −10% without) and the two did not differ significantly (P = 0.186).
Take the grams per hour from the ladder, not from here (SYNTH-02). Starting before hunger arrives follows from the mechanism — blood glucose held — not from this trial.
Fuelling does not buy back pacing. VT1 power fell in the fed condition too, so conservative pacing and durability work stay on the list (SYNTH-32).
Limitations
n = 12 trained cyclists/triathletes, crossover, single 150-min preload — a controlled laboratory model of durability, not a race. The VT1 comparison with carbohydrate rests on n=11.
Carbohydrate versus no carbohydrate is a deliberately extreme contrast; it does not identify a dose, a timing or a product, and no athlete races unfuelled by choice.
The outcome is the moderate-to-heavy transition power after a fixed preload — a physiological boundary, not finishing time; the severe-intensity (5-min TT) difference was not significant.
10 males and 2 females are not analysed separately at this sample size; sex-specific substrate differences cannot be resolved.
Gut tolerance, heat and real-race variability are all excluded by the laboratory design, and each of them changes what is achievable in practice.
How this entry was checked and changed
Why this level
regraded 2026-09-26 from A-: crossover, n=12
Content correction 2026-09-27
Key Results table with placeholders ("Significant decline", "p<0.05") -> replaced with the abstract's numbers: VT1 229 -> 225 W (−3 ± 2%) with CHO vs 216 W (−6 ± 4%) without, P = 0.019 between conditions.
Added the 5-min TT result the entry omitted: fell in both conditions (−4% vs −10%) with no significant difference (P = 0.186).
Mechanism bullets (glycogen sparing, Type II recruitment, central fatigue) -> relabelled as inference; only blood glucose was measured.
"~60 g/h" multiple-transportable bullet -> relabelled "Not from this paper", pointed to SYNTH-02 (which carries the dose ladder) instead of REF-008.
Descriptions of REF-144 repeated its pre-2026-09-26 version (muscle biopsies, glycogen/fibre-type depletion, fat oxidation doubling, power "preserved/maintained" at 100 g/h). The corrected entry took no biopsies and reports 6-min power FALLING ~10% after 4 h at 100 g/h; descriptions updated.
2026-09-28: added Protocol from the abstract (Europe PMC PMID 39709586).
2026-10-01: citation of the superseded pointer SYNTH-12 repointed to SYNTH-32, which carries the cited content.