REF-780 · Ehrström et al., 2018 · Medicine & Science in Sports & Exercise, Vol. · Paper · PubMed

Short Trail Running Race: Beyond the Classic Model for Endurance Running Performance

Blimited evidenceMeasured on highly trained athletesWritten before October 2026, being re-checked

Nine highly trained trail runners ran an official 27-km trail race and completed laboratory tests: VO2max, %VO2max at the ventilatory threshold, running economy on the level and on a +10% slope, maximal concentric and eccentric knee-extension torque, a local-endurance fatigue index (FI), and time to exhaustion at 87.5% of the velocity at VO2max.

FI (r = 0.91) and VO2max (r = -0.76) correlated most strongly with race time; the other variables did not correlate significantly. The classic model (VO2max, %VO2max at VT, level economy) predicted race time poorly (R = 0.48), while adding FI and uphill economy in place of level economy raised the prediction to R = 0.98.

Participants

n=9 (abstract: "nine highly trained trail runners"), described as a homogeneous group. Sex, age and race times are not given in the abstract.

Protocol

Official trail race of 27 km; race time as the dependent variable.
Laboratory: VO2max, %VO2max at VT, level running economy (RE0%), running economy on a +10% slope, maximal voluntary concentric and eccentric knee-extension torque, local endurance by fatigue index (FI), time to exhaustion at 87.5% of the velocity associated with VO2max.
Simple regression and commonality analysis (unique and common contributions of each predictor).

Key Results

Correlations with race time: FI r = 0.91; VO2max r = -0.76. The other variables, including maximal knee-extension torque, were not significantly correlated.
Classic model (relative VO2max, %VO2max at VT, RE0%): R = 0.48.
Adding FI and uphill RE (+10% slope) instead of level RE: R = 0.98.
Commonality analysis: FI unique contribution 49.8% and VO2max 20.4% of the total effect; their common contribution 26.9%.

Practical Application

In nine highly trained trail runners, race time in a 27-km trail race was best explained by local endurance (fatigue index, r = 0.91) and VO2max (r = -0.76); the classic VO2max-threshold-level-economy model predicted poorly (R = 0.48), while adding the fatigue index and economy on a +10% slope raised prediction to R = 0.98 (correlational). For short trail races, the legs' ability to resist fatigue and uphill economy matter alongside VO2max; flat-road tests alone underrate what decides a trail race.
Maximal concentric and eccentric knee-extension torque did not correlate with race time; what mattered was how well the muscle held up over repeated efforts, not peak strength.
Test on the gradient you race on: uphill economy (+10% slope) predicted better than level economy.
Inference, not tested here: training that builds local endurance of the quadriceps (sustained climbing, repeated descents, strength-endurance work) is the obvious lever, but this study measured associations and trained nobody.
Not from this paper; the base's own practice: heavy strength work stays in the programme for economy and injury resilience (SYNTH-44); this study adds local endurance, it does not replace strength.

Limitations

Nine runners, a homogeneous highly trained group: correlations in so few runners are unstable, and a near-perfect R = 0.98 in nine runners is likely to overfit.
One race of 27 km; longer or more technical races may depend on other factors.
Cross-sectional: no training was given, so which quality to train is inference.
The fatigue-index protocol and the course profile are not described in the abstract.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level

correlational, n=9

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