Dynamics of the power-duration relationship during prolonged endurance exercise and influence of carbohydrate ingestion
Participants
n=16 participants (the abstract does not report sex split or training status)
Protocol
3-min all-out test (3MT) giving end-test power (EP ≈ CP) and work above EP (WEP ≈ W') in five conditions:
1. Control (no prior exercise)
2. Immediately after 40 min of heavy-intensity cycling, placebo drink
3. After 80 min of heavy-intensity cycling, placebo drink
4. After 2 h of heavy-intensity cycling, placebo drink
5. After 2 h of heavy-intensity cycling while consuming CHO at 60 g/h
The CHO arm exists only at 2 h; there is no CHO condition at 40 or 80 min
Muscle glycogen depletion was measured (NEW & NOTEWORTHY: CHO preserved CP "without altering muscle glycogen depletion")
Key Results
| Parameter | Control | 40 min (PLA) | 80 min (PLA) | 2 h (PLA) | 2 h (CHO 60 g/h) |
|---|---|---|---|---|---|
| EP / CP (W) | 260 ± 37 | 268 ± 39 (ns) | 260 ± 40 (ns) | 236 ± 47 (−9%, P<0.05) | 254 ± 49 (reduction negated) |
| WEP / W' (kJ) | 17.9 ± 3.3 | 16.1 ± 3.3 (ns) | 14.7 ± 2.9 (−18%, P<0.05) | 13.8 ± 2.7 (−23%, P<0.05) | 13.5 ± 3.4 (no CHO effect, ≈ −25% vs control) |
CP was unchanged through 80 min of heavy-intensity cycling and fell 9% by 2 h on placebo
W' declined earlier: no significant change at 40 min, then −18% at 80 min and −23% at 2 h
CHO 60 g/h negated the 2-h CP reduction (254 W vs 236 W on placebo) but had no effect on W' (13.5 kJ)
CHO preserved CP without altering muscle glycogen depletion (percent changes above are computed from the abstract's means)
Mechanisms
The abstract reports different time courses for CP and W' and that CP is "sensitive to CHO availability"; glycogen depletion did not differ detectably with and without CHO, so glycogen sparing does not explain the CP protection in this trial (pooled crossovers find a small sparing, REF-1123)
Inference, not tested: exogenous CHO availability (blood glucose / oxidation) rather than the muscle glycogen pool sustains CP late in prolonged exercise; W' declines for reasons CHO ingestion does not touch. The paper's abstract does not name the mechanism.
Practical Application
In n=16 participants doing 2 h of heavy-intensity cycling, CP (3MT end-test power) was unchanged at 40 and 80 min and fell 9% at 2 h (260 → 236 W) on placebo; 60 g/h carbohydrate negated that fall (254 W) but did nothing for W', which had already dropped 18% at 80 min and 23% at 2 h and was 13.5 kJ with CHO — carbohydrate protects the sustainable ceiling late in a long ride, not the anaerobic reserve.
The pacing rule that follows: from about 80 min of hard work the athlete has less W' to spend and carbohydrate does not bring it back, so a surge above CP late in a ride costs more than the same surge early — pace the finish by CP, not by what was possible fresh.
Beyond 2 h nothing was measured; extrapolating the CP curve to a 5-h event is a guess, not a result. CHO was tested only at the 2-h point, so whether it also changes the 80-min W' drop is unknown.
Limitations
3-min all-out test (3MT) for CP determination: validated but differs from traditional multi-bout CP protocol; may slightly underestimate "true" CP, especially in fatigued state
60 g/h CHO dose: lower than modern race intakes (REF-144 tested 100 g/h, REF-333 120 g/h); study may underestimate the full CHO benefit
CHO tested only at the 2-h time point — no CHO arm at 40 or 80 min, so the time course of the CHO effect is unknown
Heavy-domain constant load for 2h is non-ecological—real races alternate domains
n=16 with no training status, sex split or VO2max in the abstract; population details are full text only
W' mechanism is not identified in the abstract; more recent work (REF-131) shows W' reconstitution kinetics are multi-factorial
How this entry was checked and changed
Why this level
regraded 2026-09-26 from A: crossover-style repeated measures, n=16
Content correction 2026-09-27
"W' fell ~13% at 80 min and ~22% at 2 h in both conditions" -> W' (WEP) fell 18% at 80 min (14.7 kJ) and 23% at 2 h (13.8 kJ) on placebo; with CHO it was 13.5 kJ at 2 h (no CHO effect).
"Crossover: each condition with CHO and placebo", "p<0.001 time × CHO" -> CHO (60 g/h) was tested only at 2 h; no interaction statistic is in the abstract.
"CHO maintains glycogen → CP preserved" and "no muscle glycogen measurement" -> CHO preserved CP without altering muscle glycogen depletion (glycogen was measured).
"Tier 4-5, 8 men 8 women" -> the abstract states only "sixteen participants"; Tier set to 2-3 and sex split removed.
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.
Cross-reference labels pointed at the wrong entry or named the wrong author (checked against each cited entry's byline); repointed to the entry the label describes, or removed where the base holds no such paper.
Cross-reference description repeated a claim that the cited entry no longer makes (it was corrected against its abstract); description updated to the cited entry's current content.
Cross-reference descriptions checked against the cited entries' current content; wrong years, wrong entries and claims the cited entry does not make were corrected.
Revision 2026-10-13: "the CP-protecting effect is not glycogen sparing" -> glycogen sparing does not explain the CP protection in this trial; cross-check with REF-1123 (meta-analysis of 31 crossovers: a small pooled sparing that single trials of this size cannot detect).