A 166 km mountain ultra cut maximal knee-extensor and plantar-flexor force by about 35-39%, through both central (voluntary activation) and peripheral (excitation-contraction coupling) failure
And force was back to baseline within 16 days, mostly within 9
Participants
n=22 experienced ultra-marathon runners tested before and immediately after the race; 11 of them followed at 2, 5, 9 and 16 days.
Protocol
Race: 166 km mountain ultra-marathon with 9500 m of positive and negative elevation change.
Neuromuscular function of knee extensors (KE) and plantar flexors (PF), plus blood markers of muscle damage and inflammation.
Key Findings
Maximal voluntary force fell by 35% for KE [95% CI −28 to −42%] and 39% for PF [−32 to −46%] immediately after the race.
Central component: maximal voluntary activation fell, mainly for KE (−19% [−7 to −32%]).
Peripheral component: moderate to large reductions in compound muscle action potential amplitude, high-frequency doublet force and low-frequency fatigue (an index of excitation-contraction coupling failure) in both muscle groups — the authors note E-C coupling failure had never been described after prolonged running.
Muscle damage and inflammation: creatine kinase 144 ± 94 → 13,633 ± 12,626 UI/L; myoglobin 32 ± 22 → 1,432 ± 1,209 µg/L; C-reactive protein <2.0 → 37.7 ± 26.5 mg/L.
Recovery: neuromuscular function had returned to baseline by 16 days, with most of the recovery within 9 days.
Authors' conclusion: the force loss is multi-factorial.
Practical Application
After a 166 km mountain ultra (9500 m up and down), 22 experienced runners lost 35-39% of maximal leg force, from both central and peripheral causes, with creatine kinase up from 144 to 13,633 UI/L; force returned to baseline by 16 days, most of it within 9. Plan roughly two weeks before hard or strength-heavy training after an event like this.
Inference, not tested: the study measured before and after the race, not during it, so it does not by itself explain late-race slowing.
Not from this paper; the base's own practice: pace conservatively early and build eccentric/downhill durability beforehand (REF-660 carries the downhill-exposure evidence).
Limitations
One event, uncontrolled pre/post design; only 11 of 22 followed through recovery.
Magnitude will vary with terrain, duration and training status.
How this entry was checked and changed
Content correction 2026-09-27
"Large, long-lasting reductions ... driven mainly by peripheral fatigue" -> the abstract calls the loss multi-factorial (central −19% activation in KE plus peripheral E-C coupling failure) and reports full recovery by 16 days, most within 9; wording and title corrected.
Added the abstract's numbers (n=22/11, 166 km, 9500 m, −35%/−39% MVC, CK/myoglobin/CRP).
"Explains late-race slowing" -> not measured (pre/post only); labelled as inference. Pacing and eccentric-prep advice labelled as the base's own practice.