Verbier X-Alpine Finish Time Predictor

Trail Verbier St-Bernard by UTMB - X-Alpine covers 140.3 km with around 9,127 m of elevation gain, starting in Verbier, Switzerland. The overall cutoff is 41 hours 30 minutes.

Crew access is allowed at Champex (37.7 km), La Fouly (60.6 km), Col des Chevaux (77.2 km), Bourg-St-Pierre (89.2 km), Cabane Brunet (108.9 km), Lourtier (127.5 km) and La Chaux (133.6 km). Drop bags are available at Bourg-St-Pierre.

Checkpoint data approximate - verify against the current official race guide at verbier.utmb.world before your race.

The classic Riegel formula (T2 = T1 × (D2/D1)^1.06) was derived from road race data. It assumes distance is the only factor in fatigue - ignoring elevation, terrain friction, and ultra-specific physiological degradation. For mountain trail races, these factors dominate.

ITRA km-effort normalises trail races by effort rather than distance. A 50km race with 3,000m of gain has a km-effort of 80 - equivalent in effort to an 80km flat race. Our version also accounts for descent cost (loss_m / 150), because steep descents cause significant eccentric muscle damage (Minetti, 2002) that isn't free.

Ultra fatigue: Millet et al. (2011) documented progressive neuromuscular degradation in ultra-marathons - central fatigue, GI distress, and eccentric muscle damage compound over time. The fatigue exponent in our prediction scales from 1.06 (≤marathon) to 1.15 (>100km), producing increasingly conservative predictions as distance grows. The stepped exponents beyond marathon distance are TrailMath heuristics, not published constants - they represent a conservative extrapolation of Millet's qualitative findings, not empirically derived values.

Terrain multipliers are practical heuristics, not peer-reviewed constants. Technical trail is approximately 1.30× slower than road pace for the same flat effort - accounting for footplacement, rocks, roots, and lateral stability demands. These multipliers are applied relative to your known race's terrain, so comparing trail-to-trail or road-to-road eliminates the terrain effect and leaves only effort differences.

How to use this: Choose a known result you're proud of and that reflects your current fitness. A race from 6 months ago still works if your training hasn't changed significantly. The prediction gives a range - aim for somewhere between optimistic and conservative based on your training specificity for the target race.

ITRA. km-effort formula. International Trail Running Association. Riegel PS. (1977). Athletic records and human endurance. American Scientist. Millet GY et al. (2011). Neuromuscular consequences of an extreme mountain ultra-marathon. PLoS ONE. Minetti AE et al. (2002). J Appl Physiol. 93(3):1039-46.