Trail Training for the Mont Blanc Marathon: 42 and 90 km Training Plan

The Mont Blanc Marathon requires neither crampons nor a rope: it's a trail running event, where the difficulty comes from cumulative elevation gain and effort duration, not glacier technique. Preparing for the ascent of the summit itself (the Goûter normal route, roped travel, altitude above 4,000 m) follows an entirely different logic — see our dedicated guide to physical preparation for high mountains.

A reference plan for a 40 to 45 km trail with around 3,000 m of elevation gain — a profile close to the Mont Blanc 42 km (2,540 m D+) — spans 12 weeks, with 3 running sessions and 1 to 2 strength training sessions each week. Long runs build up progressively to around 2h30 on uneven terrain. For the 90 km (≈ 6,200 m D+), training requires a higher volume and an already-established trail running base; for the 23 km or 10 km, a shorter plan is enough.

Hill sessions (repeats uphill at varying intensity) build the power needed on sections like the aiguillette des Posettes or the technical parts of the 90 km. The descent deserves dedicated training in its own right: the quadriceps brakes the body through eccentric contraction, a movement far more damaging to muscle fibers than the effort of climbing — neglecting this specific training is a common cause of debilitating muscle soreness after the race.

Start elevation-gain runs with short sessions, in the range of 200 to 400 m D+, before increasing progressively, rather than jumping straight into long outings. Proprioception work and strength training (core work, squats, stair climbing) complement regular runs to limit injury risk on uneven terrain.

Plan for 500 to 800 mL of fluid per hour of effort, adjusted to the forecast weather — a benchmark to test in training, never discovered for the first time on race day. The food reserve is part of the mandatory kit checked at bib pickup for the semi-autonomous races (23, 42, 90 km): train yourself to eat at race pace, not just while fasted or at rest.