UTMB Aid Station Planner

The Ultra-Trail du Mont-Blanc is a 171km loop circumnavigating the Mont-Blanc massif through France, Italy, and Switzerland, with 10,000m of elevation gain and loss. Starting and finishing in Chamonix, it is one of the most competitive and sought-after ultra-trail races in the world.

Key sections and where the race is won and lost. The opening 50km to Les Chapieux are deceptively demanding - three significant cols (Col du Voza, Col du Bonhomme, Col de la Croix du Bonhomme) set the tone. Most DNFs happen in the 45km section between Courmayeur (79km) and Champex-Lac (125km), which has no crew access except La Fouly (116km). The final climb from Vallorcine to La Flegere (149-161km) at 1200m of gain after 150km of racing is where the race truly ends for many runners.

Crew access points: Saint-Gervais (22km), Courmayeur (79km), Champex-Lac (125km), Vallorcine (149km). Drop bags allowed at: Les Contamines (31km), Les Chapieux (50km), Courmayeur (79km), Champex-Lac (125km), Trient (139km).

Pacing guidance. The planner uses TrailMath's km-effort model to distribute your goal time across segments proportionally to their effort cost. For a 30-hour finish, expect roughly: Saint-Gervais 3:30, Courmayeur 13:00, Champex-Lac 21:00, Vallorcine 26:30. These are effort-proportional estimates - adjust for the night penalty (TrailMath plans for roughly 15-20% between 21:00 and 05:00, weighted toward the 02:00-04:00 low) and your individual strengths on climbs vs descents.

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

Most runners build race pacing plans by dividing total distance evenly - which ignores the fact that an uphill kilometre takes far longer than a flat one. This planner uses TrailMath's enhanced km-effort model to distribute your goal time proportionally by effort, not by distance.

The km-effort formula for each segment is: distance_km + gain_m/100 + loss_m/150. This is TrailMath's extension of the standard ITRA gain-only formula, which adds descent cost based on Minetti's finding that steep technical descents carry real metabolic load. A 5km segment with 500m of gain and 200m of loss has an effort of 5 + 5 + 1.3 = 11.3 km-effort - equivalent to running 11.3km flat. Time is allocated proportionally to this effort score.

Why gain and loss have asymmetric costs. Minetti et al. (2002) mapped the metabolic cost of inclined locomotion across gradients from -45% to +45%. The key findings: metabolic cost rises steeply above 15-20% uphill grade, making power hiking more energy-efficient than running on steep climbs. On descents, eccentric muscle loading (quads acting as brakes) creates its own metabolic cost - steep technical descents are far more demanding than the same gradient on a smooth fire road. The gain/100 + loss/150 asymmetry in the formula reflects this - gain is more costly per metre than loss, but loss is not free.

Power hiking threshold is flagged at segments where your computed pace exceeds 12 min/km (19 min/mile). This threshold corresponds to the crossover point where walking biomechanics become more efficient than running on steep uphill terrain. Strategic power hiking on marked segments preserves leg muscle for descents and reduces overall race time compared to running everything.

This km-effort model is the same formula used in TrailMath's training engine for load calculation (following Dan Johnston's asymmetric elevation scoring methodology), ensuring consistency between how your training load is measured and how your race effort is planned.

Minetti AE et al. (2002). Energy cost of walking and running at extreme uphill and downhill slopes. J Appl Physiol. 93(3):1039-46. Minetti AE et al. (1995). Mechanical determinants of gradient walking energetics in man. J Physiol. 481(Pt 1):235-43. ITRA. km-effort formula. International Trail Running Association. itra.run