What Is This?
Cycling durability is the ability to keep producing race-useful power after fatigue has accumulated.
A rider can look strong when fresh and still be fragile after two, three, or four hours. That gap matters because bike racing is not a lab test done on rested legs. The decisive effort often comes after hours of work, repeated surges, glycogen use, dehydration, heat stress, and mental load.
Two 2026 cycling physiology papers sharpen the model.
One paper tested whether caffeine could protect late-race performance after a simulated cycling race. Junior trained cyclists performed an 8-minute time trial fresh, then after roughly 90 minutes of work-matched field riding. Placebo showed a clear drop from fresh power. Caffeine did not fully prove superiority versus placebo, but the decline was smaller and exceeded the authors’ smallest worthwhile change estimate.
The second paper tested low versus high carbohydrate availability in endurance-trained female cyclists. Low carbohydrate availability reduced power at the first ventilatory threshold, reduced gross cycling efficiency, and changed muscle activation signals during submaximal cycling. The authors’ interpretation was practical: carbohydrate availability matters not just for final sprints, but for the power you can produce at the transition from moderate to heavier work.
The simple model: durability is not only fitness. It is fitness under depletion. Fuel availability, fatigue history, and the timing of the effort change what your numbers mean.
Why Does It Matter?
Most riders measure themselves when they are fresh.
They ask:
- What is my FTP?
- What is my 5-minute power?
- What is my VO2 max?
- What is my best 8-minute or 20-minute test?
Those numbers matter, but they are incomplete. Racing asks a different question: what can you still do after the race has already taxed the system?
That is durability.
Durability explains why two riders with similar headline metrics can separate late in a ride. One rider preserves threshold power, repeatability, economy, and decision-making. The other still has a good fresh test, but their usable power collapses once glycogen falls, muscle recruitment changes, and the cost of producing the same watts rises.
This is especially relevant for Jamie’s cycling model because Garmin-style summaries can flatten the ride into calories, training load, heart rate zones, and average power. Durability forces a better question:
Did today’s ride build the ability to produce useful power late, or did it just add fatigue?
The Two Papers
1. Caffeine and durability after a simulated race
Paper: Alejo et al., Effects of Caffeine on Durability After a Simulated Race in Trained Cyclists: A Field-Based Cross-Over Randomized Controlled Trial, International Journal of Sport Nutrition and Exercise Metabolism, 2026. DOI: 10.1123/ijsnem.2025-0091. PMID: 41248625.
Design: Thirteen well-trained junior cyclists completed an 8-minute time trial fresh and after two work-matched field sessions designed to simulate a short cycling race: about 90 minutes and roughly 20 kJ/kg of work. During the race-simulation sessions, they consumed either caffeine at 6 mg/kg or placebo about 60 minutes before the time trial.
Result: Average time-trial power fell in placebo compared with fresh conditions: 352 ± 34 W versus 367 ± 36 W. In the caffeine condition, power was 363 ± 40 W and was not significantly lower than fresh. The direct caffeine-versus-placebo comparison did not reach statistical significance, but the difference was moderate, about 3.1%, and above the study’s estimated smallest worthwhile change of 2%. Source: https://pubmed.ncbi.nlm.nih.gov/41248625/
Interpretation: This does not prove “caffeine fixes durability.” The sample was small, the riders were juniors, and the caffeine-versus-placebo comparison missed conventional significance. The useful takeaway is narrower: caffeine may partly protect late-race time-trial power, but the result should be treated as suggestive rather than settled.
For a rider, the lesson is not to worship caffeine. It is to notice the measurement frame. The study did not only ask whether caffeine improves a fresh effort. It asked whether caffeine helps preserve output after race-like work. That is the right question.
2. Low carbohydrate availability and the moderate-to-heavy transition
Paper: Main et al., Low carbohydrate availability reduces power output at the moderate-to-heavy transition, impairs efficiency, and increases median power frequency during cycling in females, European Journal of Applied Physiology, 2026. DOI: 10.1007/s00421-026-06260-3. PMID: 42228164.
Design: Nine well-trained female cyclists completed a randomised, counterbalanced crossover study. They did glycogen-depleting exercise about 24 hours before testing, then followed either high carbohydrate intake of at least 9 g/kg or low carbohydrate intake of at most 1 g/kg. They then completed an incremental cycling test and a three-minute all-out test.
Result: Low carbohydrate availability reduced power at the first ventilatory threshold: 133 ± 24 W versus 152 ± 28 W, a mean drop of 19 W. Gross cycling efficiency during submaximal riding was lower in the low-carbohydrate condition. The study also found changes in electromyographic median power frequency, with no difference in end-test power during the three-minute all-out test.
Interpretation: Low carbohydrate availability made the same submaximal cycling less efficient and reduced the power associated with the moderate-to-heavy transition. The authors suggest this may reflect greater recruitment of higher-threshold motor units to compensate for glycogen-depleted fibres.
This matters because it shifts carbohydrate from a “bonk prevention” topic into a durability topic. Carbohydrate availability can change the power you can produce before the ride even reaches maximal effort.
The Better Mental Model
Fresh performance is the ceiling. Durability is how much of the ceiling survives fatigue.
A rider’s late-ride power can fall for several overlapping reasons:
- glycogen depletion
- reduced carbohydrate availability
- lower gross efficiency
- cardiovascular drift
- heat stress
- dehydration
- muscle damage or local fatigue
- reduced anaerobic contribution
- changes in motor-unit recruitment
- mental fatigue and rising perceived effort
The key is that these do not show up as one clean metric. They show up as changed relationships between metrics.
Examples:
- Same power, higher heart rate.
- Same heart rate, lower power.
- Same power, higher perceived effort.
- Same interval target, worse repeatability.
- Same nutrition plan, different outcome in heat.
- Same FTP, much worse 5-minute power after three hours.
That is why durability is a systems property. It is not just aerobic fitness. It is aerobic fitness plus substrate availability plus fatigue resistance plus pacing plus cooling plus gut tolerance plus recovery.
How This Changes Training
Stop treating all watts as equivalent
A 300 W effort fresh is not the same as a 300 W effort after three hours.
The second version carries more information. It tells you what power remains when the system is already taxed. For performance, late-ride power is often more predictive than a flattering fresh number.
Fuel the sessions that need fueling
Low-carbohydrate training can have a place when used deliberately. But hard cycling with low carbohydrate availability is not free. The Main et al. paper shows that low carbohydrate availability can reduce threshold-transition power and efficiency in trained female cyclists.
Practical rule: if the session is meant to produce quality, intensity, repeatability, or race-specific durability, underfueling can corrupt the signal. You may complete the ride but train a compromised version of the target.
Test durability, not just freshness
Useful rider questions:
- What is my 5-minute power fresh?
- What is my 5-minute power after 2-3 hours?
- How much does threshold power drift after accumulated work?
- How much carbohydrate per hour do I tolerate at race intensity?
- Does higher carbohydrate intake preserve late power?
- Does caffeine help late performance for me, or just raise arousal?
- Do I fade because of legs, gut, heat, pacing, or fuel?
That last question matters. “I faded” is not a diagnosis.
What Jamie Should Take From It
The useful takeaways are practical.
Durability is the missing layer beneath headline fitness. FTP and VO2 max matter, but the race-relevant question is what remains after fatigue.
Carbohydrate availability affects more than bonking. In the female cyclist study, low carbohydrate availability reduced power at the first ventilatory threshold and impaired gross efficiency.
Caffeine is a possible late-race aid, not a foundation. The caffeine paper suggests it may attenuate late performance loss, but the evidence is not strong enough to treat it as a guaranteed fix.
Late-ride testing beats dashboard vanity. A good cycling file should ask how power, heart rate, RPE, and fueling interacted across time, not just whether the average numbers looked impressive.
Fuel is part of the training stimulus. The same ride under high versus low carbohydrate availability is not physiologically identical.
A Simple Field Protocol
For a serious amateur rider, the cleanest experiment is not complicated.
Pick a repeatable route or trainer session:
- Ride 2 hours endurance/tempo at controlled intensity.
- Fuel one version normally, for example 60-90 g carbohydrate/hour if tolerated.
- Fuel another version lower, only if safe and appropriate.
- Finish with a fixed 5-minute or 8-minute effort.
- Compare power, heart rate, RPE, cadence stability, and how the final effort feels.
Do not overinterpret one trial. Repeat it. The question is whether a pattern appears.
If late power improves with better fueling, that is not weakness. That is the engine being supplied properly.
Limits
Both 2026 studies are small. The caffeine paper involved thirteen junior trained cyclists. The carbohydrate-availability paper involved nine well-trained female cyclists. They are useful mechanism-and-signal papers, not universal prescriptions.
The right use is not: “everyone should take 6 mg/kg caffeine” or “low-carb training is bad.”
The right use is: measure late-ride performance in context, and treat carbohydrate availability as one of the variables that changes durability.
Sources
- Alejo LB, Sánchez-Redondo IR, Revuelta C, de Pablos R, Ibañez M, Valenzuela PL. Effects of Caffeine on Durability After a Simulated Race in Trained Cyclists: A Field-Based Cross-Over Randomized Controlled Trial. International Journal of Sport Nutrition and Exercise Metabolism. 2026. DOI: 10.1123/ijsnem.2025-0091. PMID: 41248625.
- Main E, Yoon S, James SL, Mellor KM, Brick MJ, Leigh WB. Low carbohydrate availability reduces power output at the moderate-to-heavy transition, impairs efficiency, and increases median power frequency during cycling in females. European Journal of Applied Physiology. 2026. DOI: 10.1007/s00421-026-06260-3. PMID: 42228164.
- Mateo-March M, et al. The Relationship between Physiological Characteristics and Durability in Male Professional Cyclists. Medicine & Science in Sports & Exercise. 2023. DOI: 10.1249/mss.0000000000003024. PMID: 35977108.
- Valenzuela PL, et al. Substrate utilization and durability during prolonged intermittent exercise in elite road cyclists. European Journal of Applied Physiology. 2024. DOI: 10.1007/s00421-024-05437-y. PMID: 38441690.
- Maunder E, et al. Durability, fatigability, repeatability, and resilience in endurance sports: definitions, distinctions, and implications. Journal of Applied Physiology. 2025. DOI: 10.1152/japplphysiol.00343.2025. PMID: 40590809.
- Jones AM, et al. Defining physiological resilience and durability in the context of endurance performance modeling. Journal of Applied Physiology. 2025. DOI: 10.1152/japplphysiol.00671.2025. PMID: 41396096.