REF-459 · Abbiss & Laursen, 2005 · Sports Medicine, Vol. · Paper · PubMed

Models to explain fatigue during prolonged endurance cycling

Sports Medicine review cataloguing eight linear fatigue models and their integration into a complex-systems model (foundation of PMEP)

B+moderate evidenceMeasured on a mixed groupWritten before October 2026, being re-checked

Scope

Cycling performance may be limited by numerous physiological, biomechanical, environmental, mechanical and psychological factors.

From over 2000 manuscripts on fatigue, a number of cause-and-effect models have been developed; the review outlines these "linear" models, addresses how each may influence the development of fatigue during prolonged cycling, and closes by showing how they might be integrated into a more recently proposed nonlinear complex-systems model of exercise-induced fatigue.

Key Findings — The Eight Linear Fatigue Models (as listed in the abstract)

1. Cardiovascular / anaerobic model

Limitation by O₂ delivery (cardiac output × arterial O₂ content) and anaerobic capacity; substrate-level phosphorylation when O₂ supply is exceeded (mechanistic detail: full text; not checked against the abstract)
Best suited to short-to-medium durations, weaker for ultra-endurance

2. Energy supply / energy depletion model

Glycogen depletion (muscle and liver) → fatigue; foundation: Bergström & Hultman 1967 REF-452
Substrate switching as glycogen drops; falling blood glucose as a central signal
Caveat: glycogen depletion is not always coincident with fatigue at moderate intensity

3. Neuromuscular fatigue model

Reduced central drive, motor-unit recruitment failure, neuromuscular-junction and excitation–contraction changes
Hard to dissociate from peripheral metabolic factors

4. Muscle trauma model

Eccentric contractions → sarcomere disruption and an inflammatory cascade that reduces force
Cycling has less eccentric component than running, so its weight is smaller here

5. Biomechanical model

Declining gross efficiency and pedalling smoothness, postural changes raising metabolic cost (magnitudes are not in the abstract; see Hopker/Coyle efficiency entries REF-076, REF-077, REF-444)
Cause vs consequence of fatigue is debated

6. Thermoregulatory model

Core-temperature rise → reduced central drive; cardiovascular strain from skin vs muscle perfusion competition; heat accelerates the other mechanisms
Heat acclimation as protection (REF-001, REF-002)

7. Psychological / motivational model

Motivation, perception of effort and decision-making shape the point at which the athlete slows or stops

8. Central governor model (Noakes)

Effort regulated by the CNS on the basis of multiple afferent inputs; anticipatory regulation to prevent catastrophic failure; RPE as the integrating signal

Integration — complex-systems model (abstract): the linear models above provide afferent feedback that a central governor integrates into the unconscious perception of fatigue; fatigue is then an emergent, nonlinear outcome rather than the failure of one system.

Practical Application

Narrative review (Abbiss & Laursen 2005): from over 2000 fatigue manuscripts, eight cause-and-effect models of fatigue in prolonged cycling are catalogued — cardiovascular/anaerobic, energy depletion, neuromuscular, muscle trauma, biomechanical, thermoregulatory, psychological/motivational and central governor — and then integrated into a complex-systems model in which these feed afferent signals that a central governor turns into the perception of fatigue. Meaning: there is no single "limiter" in a long ride; training and race plans have to address several systems, and pacing is ultimately regulated by perception.
Justifies multi-component training prescriptions — each model points to a different adaptation target
Teaching frame for the PMEP framework (KIW 2026)
Race analysis: ask which models matter most for THIS event before choosing what to train
Explains why "VO₂max + threshold" testing under-predicts long-event performance — those tests probe one model
Not from this paper; the base's own practice: shorter events lean on the cardiovascular/anaerobic and neuromuscular models, multi-hour events on energy depletion, thermoregulation and muscle trauma, and ultra events on all of them with the central governor integrating — see SYNTH-10 and SYNTH-32

Limitations

Narrative review, no systematic method; 2005 — pre-dates the durability concept (Maunder 2021), later brain-side fatigue work (Marcora 2009+), DFA α1 (Rogers 2021)
Heavy focus on cycling — generalizability to running/swimming/skiing requires translation
Presents the linear models as parallel hypotheses; the complex-systems integration is proposed, not tested
Limited treatment of sex-specific differences and of ultra-endurance where additional mechanisms emerge (sleep, sodium, gut)
Largely conceptual; specific intervention prescriptions limited
How this entry was checked and changed
Why this level

regraded 2026-09-27 from A: authoritative narrative review, no systematic method

Content correction 2026-09-27
"Seven fatigue models" -> abstract lists eight linear models (psychological/motivational and central governor are separate) plus the complex-systems integration; sections renumbered.
"1000+ citations", "gross efficiency ~2-3% drop over 2+ hours", "critical for events >60 min in heat", and the duration-by-model decision table (<30 s … >8 h) -> not in the abstract; removed, the event mapping kept as one line of the base's own practice.
Level A -> B+ (narrative review); added Tier/Sport lines and an abstract-based lead.
Cross-reference pointed at an entry whose content does not match the label (checked against the cited entry); repointed or relabelled.
2026-10-01: cross-reference repointed from a merged framework to the one that replaced it (SYNTH-01→31, 05→34, 09→70, 12/15→32, 19→26).
2026-10-01: cross-reference to SYNTH-13 no longer names an archetype — that model was retired as an unvalidated composite.
2026-10-01: citation of the superseded pointer SYNTH-12 repointed to SYNTH-32, which carries the cited content.