cycling-training/references/durability.md

Durability / fatigue resistance

Load this doc when: the question is about fatigue resistance, why late-race power fades, training the ability to hold power deep into long efforts, or running the durability field test.

Data/knowledge split: the MCP server gives you the kJ, power curves, and fatigued-vs-fresh efforts. This doc explains why fatigued-state power matters and how to train it.

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Durability is a distinct, trainable quality

"Durability" is the time of onset and the magnitude of deterioration in physiological-profiling variables (thresholds, efficiency, power) over the course of prolonged exercise — a quality that should be profiled separately from fresh-state numbers, because two riders with identical fresh profiles can fall apart very differently after several hours (Maunder et al. 2021, Sports Med 51(8):1619–1628; PMID 33886100; DOI 10.1007/s40279-021-01459-0).

Why it matters more than fresh power

• In professional cyclists across a Grand Tour, fresh mean-maximal power did not separate WorldTour from ProTeam riders — but as work accumulated (0 → 35 kJ·kg⁻¹), WorldTour riders held higher power. Fatigued-state power differentiated performance; fresh power did not (Muriel et al. 2022, Eur J Sport Sci 22(12):1797–1804; PMID 34586952; DOI 10.1080/17461391.2021.1987528).
• The fatigued power profile varies far more across a season than the fresh profile, and it tracks with training characteristics (accumulated volume/load) — meaning durability is something you build with training, not a fixed trait (Spragg, Leo & Swart 2023, Eur J Sport Sci 23(4):489–498; PMID 35239466; DOI 10.1080/17461391.2022.2049886).

The load dependency (the key training implication)

Durability depends on maintaining high overall training load, whereas fresh power can be held on reduced load. You can taper volume and keep your 5-min power; you cannot taper volume for long and keep your fatigued 5-min power. This is the empirical thrust of the Spragg training- characteristics paper (PMID 35239466); the crisp "reduced load keeps fresh power, sustained load keeps durability" phrasing is Spragg's applied interpretation of that data — cite it as such.

Physiological correlates of who is durable (higher VO2max, better gross efficiency, higher fat- oxidation) come from the companion paper (Spragg, Leo & Swart 2023, Med Sci Sports Exerc 55(1):133–140; PMID 35977108; DOI 10.1249/MSS.0000000000003024) — useful for understanding mechanism, but the trainable lever is sustained load + the practices below.

How to train durability

1. Long-term consistency and high volume. Durability is a load-dependent adaptation — it is built over blocks and lost when load drops. Protect the long ride.
2. Prolonged sessions with hard efforts placed late (fatigued-state intervals). Put the quality work after accumulated kilojoules, not at the fresh start of the ride — you are specifically training the fatigued state that discriminates performance.
3. Glycogen-sparing nutrition. Fuel long sessions to spare glycogen; the goal is training the durable state under realistic fueling, not chronic depletion. (Fatigued power is glycogen- sensitive — see the fueling caveat in data-confounds.md for why HR is unreliable here.)

⚠️ Under-researched — track individual response. The mechanism (load-dependent fatigue resistance) is well supported, but the optimal durability dose — how much accumulated work, how often, how late to place efforts — is not established. Do not assume a fixed protocol. Track each athlete's fatigued-state response and titrate.

Measure it: the fatigued-state field test

Use ../assets/field-test-durability.md. In brief:

• Establish a fresh 1-min max on a fixed hill.
• On a separate day, accumulate ~1,500 kJ (~2.5 h) of mostly-endurance riding, then repeat the same 1-min max on the same hill.
• Durability % = fatigued ÷ fresh × 100. Track the trend across a block.
• Hold the hill, gearing, kJ pre-load, and fueling constant so the comparison is valid.
• Judge from power, not HR — HR after 1,500 kJ is confounded by drift, heat, and fueling (data-confounds.md).

Discipline note

Durability matters for both road/TT and MTB, but keep absolute numbers discipline-specific. The 1,500 kJ anchor is a sensible generic default, not a validated cross-discipline constant; a masters marathon-MTB rider and an elite road pro do not share a durability dose. See mtb-xco-demands.md for how fatigue resistance shows up specifically in off-road racing.