REF-455 · Allen, Lamb, Westerblad, 2008 · Physiological Reviews, Vol. · Paper · PubMed

Skeletal muscle fatigue: cellular mechanisms

Physiological Reviews synthesis; lactate/H⁺ is "probably of limited importance", the candidates are ions, SR Ca²⁺ release and ROS

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

Scope

Repeated intense use of muscle leads to a decline in performance — muscle fatigue. Many muscle properties change during fatigue: the action potential, extracellular and intracellular ions, and many intracellular metabolites. The review catalogues the mechanisms identified as contributing to the decline of performance and asks which ones matter under which circumstances.

Key Findings (concepts)

1

The traditional explanation — accumulation of intracellular lactate and hydrogen ions impairing the contractile proteins — is "probably of limited importance in mammals." This is the review's headline position, and it is the opposite of the popular "lactic acid causes fatigue" story.

2

The alternatives the review weighs:

Effects of ionic changes (extra-/intracellular K⁺, Na⁺, Cl⁻) on the action potential
Failure of sarcoplasmic reticulum Ca²⁺ release, by several mechanisms (inorganic phosphate and glycogen depletion are discussed in the full text — not checked against the abstract)
Effects of reactive oxygen species (ROS)
3

Task specificity: many different activities lead to fatigue; a central challenge is identifying which mechanisms contribute under different circumstances

4

Translation gap: most mechanistic fatigue studies are on isolated animal tissue; applying them to intact animals and to humans (particularly in disease) is a stated open challenge

Practical Application

Narrative review (Allen, Lamb & Westerblad 2008, mostly isolated animal muscle): the classic "lactate and H⁺ impair the contractile proteins" explanation of muscle fatigue is probably of limited importance in mammals; the mechanisms the authors weigh instead are ionic changes affecting the action potential, failure of SR Ca²⁺ release, and reactive oxygen species — and which one dominates depends on the task. Meaning: do not tell an athlete that "lactic acid" made the legs fail; the cellular story is Ca²⁺ handling and ion shifts, and the human-performance translation is still open.
Inference, not tested: buffering supplements (β-alanine REF-351, bicarbonate REF-353) are usually justified by acidosis — this review weakens that rationale at the muscle-cell level; their ergogenic evidence stands or falls on the trials in those entries, not on this mechanism
Inference, not tested: creatine REF-352 and glycogen availability REF-472 connect to the SR Ca²⁺-release mechanism the review favours
Heat and cooling strategies act on central and cardiovascular fatigue, which are outside this cellular review

Limitations

Cellular focus — less on central/neural fatigue
Mostly isolated animal tissue; the authors themselves flag the translation to intact animals and humans as an open challenge
2008 — later work on Ca²⁺ leak and mitochondrial ROS has evolved
Doesn't integrate cognitive/affective fatigue (Marcora et al. work)
How this entry was checked and changed
Why this level

regraded 2026-09-27 from A: authoritative narrative review from the leading group, no systematic method; mostly isolated animal-tissue data

Content correction 2026-09-27
"H⁺ accumulation (acidosis) → enzyme inhibition" listed as a fatigue mechanism, and "buffering supplements target acidosis-related fatigue → relevant for 1-4 min efforts" -> the abstract says the lactate/H⁺ explanation is "probably of limited importance in mammals"; rewritten around the review's actual position, the supplement link relabelled as inference.
"PCr ~5 min", "glycogen 24+ h", "1-4 min", "2000+ citations" -> not in the abstract; removed.
Level A -> B+ (narrative review, largely animal tissue); added Tier/Sport lines and an abstract-based lead.
Cross-reference pointed at REF-372 (Staiano, brain endurance training) under Marcora's name; repointed to REF-370 (Marcora 2009).