Central and peripheral contributions to neuromuscular fatigue induced by a 24-h treadmill run
Twelve experienced ultramarathon runners ran on a treadmill for 24 h, with neuromuscular testing before, every 4 h and at the end. Maximal voluntary strength of the knee extensors and plantar flexors fell steadily, by 40.9% and 30.3% at the end, together with large falls in voluntary activation.
Muscle-level measures changed far less: the knee extensors' maximal force production ability fell by 10.2%, low-frequency fatigue was absent, and the compound action potential fell only in the soleus. The authors conclude that central factors mainly explain the large torque loss after ultra-endurance running, especially in the knee extensors.
Participants
n=12 experienced ultramarathon runners.
Protocol
24-h treadmill run (24TR).
Neuromuscular testing before, every 4 h during and at the end:
maximal voluntary contraction (MVC) of knee extensors (KE) and plantar flexors (PF)
maximal voluntary activation (%VA) of KE and PF
maximal compound muscle action potential amplitude (Mmax) on soleus and vastus lateralis
tetanic stimulation for low-frequency fatigue and KE maximal muscle force production ability
Key Results
Strength loss occurred throughout the run.
MVC after 24TR: KE −40.9 ± 17.0%, PF −30.3 ± 12.5% (P < 0.001).
Voluntary activation: KE −33.0 ± 21.8%, PF −14.8 ± 18.9% (P < 0.001).
Mmax fell only on the soleus; no low-frequency fatigue in any muscle group.
KE maximal force production ability: −10.2% (P < 0.001), highly variable (± 15.7%).
Practical Application
In 12 experienced ultramarathon runners, a 24-h treadmill run cut maximal knee-extensor strength by 40.9% and plantar-flexor strength by 30.3%, largely through reduced voluntary activation (−33.0% and −14.8%), while the knee extensors' own force capacity fell only 10.2%. To "after a 24-h race my legs are dead — is the muscle wrecked?": on flat ground, most of the strength loss came from the nervous system's reduced drive, not from the muscle itself.
The authors suggest the reduced neural drive may have protected peripheral function and shaped how running speed evolved over the 24 h.
Contrast with a mountain ultra: after a long mountain race, the strength loss had both central and peripheral causes (REF-662). Terrain changes the kind of damage.
Limitations
n=12; no control group; treadmill, not a race.
Large between-runner variability (e.g. voluntary activation −33.0 ± 21.8%).
Mechanistic measures only; performance is described but not tested as an outcome.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level
uncontrolled repeated measures, n=12