REF-777 · Millet, 2011 · Sports Medicine, Vol. · Paper · PubMed

Can Neuromuscular Fatigue Explain Running Strategies and Performance in Ultra-Marathons? The flush model

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

The review first covers the central and peripheral causes of the neuromuscular changes (strength loss, measured as maximal voluntary contraction) that occur in ultra-marathon running.

It then argues that maximal-contraction and stimulation measurements do not necessarily explain how speed is regulated in a real race, and proposes a holistic "flush model" of pacing: perceived exertion as a ball-cock that rises or falls with the filling rate and the water leaving through the waste pipe, plus a security reserve that prevents physiological damage.

In the model, central regulation depends not only on afferent signals from muscles and organs but also on peripheral fatigue and spinal/supraspinal inhibition, because these demand a higher central drive for the same power output.

Participants

Not applicable (narrative review). The abstract names no included studies and no pooled sample.

Protocol

First part: review of central and peripheral causes of altered neuromuscular function in ultra-marathon running, assessed with maximal voluntary contractions and maximal electrical/magnetic stimulation.
Second part: proposal of the flush model, described as applicable to all endurance activities but adapted specifically to ultra-endurance running.

Key Results

Fatigue in the review is defined as strength loss (a decrease in MVC), which depends on the type of exercise: its intensity and duration, the muscle groups involved and the type of contraction.
The review questions whether fatigue measured with maximal contractions or stimulation explains submaximal performance and speed regulation in a race.
The flush model has four components: (i) the ball-cock (or buoy), compared with the rate of perceived exertion; (ii) the filling rate; (iii) the water evacuated through the waste pipe; (iv) a security reserve that lets the runner avoid physiological damage.
The model is proposed to explain how environmental conditions, sleep deprivation/mental fatigue, pain-killers or psychostimulants, and cognitive or nutritional strategies may affect ultra-running performance.
Races covered run in multiples of 10 km, up to 1000 km in one stage; fatigue resistance is described as critical.

Practical Application

In a narrative review of neuromuscular fatigue in ultra-marathon running, Millet proposes that ultra pace is set by perceived exertion, which rises with muscle and nervous-system fatigue (because a fatigued system needs more central drive for the same speed) and is held below a protective security reserve — a model, not a tested result. Expect an ultra runner to slow because effort feels higher, not because a single system fails; anything that raises or masks perceived effort changes the pacing.
The review names sleep deprivation, mental fatigue, environmental conditions, pain-killers and stimulants, and cognitive and nutritional strategies as things that move the model. Inference, not tested here: a runner on pain-killers or stimulants may lower perceived effort without lowering the underlying fatigue, and the security reserve is exactly what those drugs could erode.
Maximal strength tests after a race describe fatigue but, on this review's argument, do not by themselves explain how a runner paced; do not read a post-race strength loss as the reason for a given race strategy.
Not from this paper; the base's own practice: in ultras, pace by effort and keep the early hours well inside what feels comfortable; fuel and sleep strategy are part of pacing, not separate topics.

Limitations

Narrative review without a stated systematic search; the included studies and their samples are not listed in the abstract.
The flush model is a conceptual proposal; the abstract reports no test of its predictions.
Written from the abstract and record metadata only (full text not read); the specific central and peripheral fatigue findings summarised in the first part are not given in the abstract.
How this entry was checked and changed
Why this level

authoritative narrative review from the leading ultra-fatigue group; the flush model itself is a proposal the paper does not test

Content correction 2026-09-27
2026-10-01: independent check against the abstract — wording brought back to what the abstract states.