Marathon du Mont-Blanc 23K
training plan
An adaptive 25K trail plan for a mountain course on trail, run in unpredictable June conditions, built around the three things Marathon du Mont-Blanc 23K actually asks of you: one long sustained climb, technical descending and a mass field. Twelve weeks written two at a time, from what you actually did in the two weeks before, and rewritten the moment you travel, get ill or something starts hurting.
This page describes the race and what its course, climate and date ask of a build. On Pro, the plan itself is written for you, from your experience, your weekly hours and your date, so two athletes entered in this race get different plans.
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Three demands, three answers
A generic 12-week 25K trail plan gets you to the start line. It has no idea about one long sustained climb, technical descending or a mass field.
On the ground, Marathon du Mont-Blanc 23K is a mountain course on trail, with 1,680 m of climbing in it. It is usually held in June, when the weather is genuinely unpredictable, and two editions running rarely feel the same. So over a 25K trail race, the vertical is the event and the distance is how long you are out in it, and the weather is the variable you prepare for, because nobody can plan around it. There will be tens of thousands starters out there with you.
- Profile
- Mountainous · trail
- Climbing
- 1,680 m · 67 m in every kilometer
- Usual conditions
- June · unpredictable
- Race season
- Summer, northern hemisphere
- Field
- Large · tens of thousands
One climb long enough to change the race
A sustained climb is a different engine from anything you meet on rolling ground: twenty minutes or more at an effort you cannot back off from, with the rest of the course still to come.
Sustained climbing intervals at threshold rather than short punchy reps, built to the length Marathon du Mont-Blanc 23K actually asks for, and rehearsed with the fatigue you will be carrying when you reach it.
Descending here is a skill you have to practice
Loose, steep or rocky descents ask for balance, braking control and nerve. Treated as recovery they cost you time and shred your legs for whatever comes after.
Repeated descent practice on terrain like the course, and eccentric strength so the legs holding you back at the end of Marathon du Mont-Blanc 23K are still the ones you started with.
The first miles belong to the crowd
A field this size means corrals, a start that takes minutes to clear, and an opening section run at whatever pace the people around you have chosen. Weaving costs more than it looks like it does.
Race-week guidance for a crowded start and an opening section paced deliberately conservatively, so the time you give away early on Marathon du Mont-Blanc 23K is time you get back later.
Getting in, and getting to the line
Adaptlete has no involvement in entry, allocation or ballots for any race. This is what the format asks of your planning.
Open entry
Entry usually stays open close to the day, which sounds relaxed and is exactly why so many people start their build six weeks out. Twelve weeks back from June puts the first week in late March.
Large field
A large field means a start pen, a gun time that is not your chip time, and a first mile you do not control, and on a mountain course the queue forms at the first singletrack and never fully clears. Over a 25K trail race, that is a long time to be running somebody else's race.
Trail
Trail, so the long sessions have to happen on ground like it. Footing, poles, descending and eating while you move are skills, and none of them are learnable on a treadmill in the last two weeks. The peak week puts climbing intervals on it, months before June.
You will be training through the northern spring
Work backwards and a twelve-week block for a June race opens around late March, running March through to June. That is the northern spring, and it is the half of the job most plans never mention. The light comes back a little faster than the weather does, so the first block is still winter and the last one is not. It is the easiest season to train in and the easiest one to overreach in, because everything suddenly feels good at once. And the last block lands in June, with mountainous ground, unpredictable conditions and a large field waiting at the end of it.
So the plan holds the ramp down while the evenings open up, and puts the biggest weeks where the daylight actually supports them rather than where enthusiasm wants them. Whatever the season takes out of two weeks, the work for one long sustained climb, technical descending and a mass field is what the rebuild puts back first.
- Weeks 1-5 March-April the weather turns mid-block; the ramp holds steady anyway
- Weeks 6-7 April-May
- Weeks 8-12 · peak and taper May-June early starts and heat; the long sessions move to the cool hours
Months assume Marathon du Mont-Blanc 23K keeps its usual June slot and that you take the full 12 weeks. Adaptlete builds from the date you enter.
A real week from a Marathon du Mont-Blanc 23K build
This is the shape of the biggest week in 12: 4-5 sessions a week, 6H 38M of training, and one session that matters more than the rest. Two of them are here because of this course and not the distance: climbing intervals for the mountainous profile, and a weather rehearsal for conditions that are usually unpredictable. The key session itself is written for one long sustained climb. For a June race, week 8 lands in May. Your version is written from your hours, your history and how far out you are.
- Every session says what it is for, in plain language
- Intensity you can scan down the week without reading
- Move any session to any day without breaking the block
| Day | Intensity | Session | Distance and duration |
|---|---|---|---|
| MON | Rest | Rest | |
| TUE | Zone 4, threshold | Climbing intervals: 4 × 10 min, hiking the steep sections | 10 km50' |
| WED | Zone 2, easy | Easy trail run | 8 km48' |
| THU | Zone 3, steady | Strength: step-downs & ankles | 40' |
| FRI | Zone 1, recovery | Weather rehearsal: it goes ahead in whatever the day hands you | 5 km30' |
| SAT | Zone 3, steady | Long trail run: a sustained climb at threshold | 21 km2H20 |
| SUN | Zone 2, easy | Time on feet: hike with vert | 10 km1H30 |
Something will go wrong.
That is the part we built for.
Nobody finishes a twelve-week build without missing a week, and March through to June is a long time to stay lucky. The plans that fail are the ones that carry on as if nothing happened.
A work trip in week 7
Hotel treadmill, nothing else? Those days get rewritten around it.
Flu in April
The block rebuilds and ramps you back. Nothing is deleted.
A niggle at week 8
Loading comes off it, the rest of your week stays. And go see someone.
Questions people actually search
How many weeks do I need to train for Marathon du Mont-Blanc 23K?
Twelve weeks is the usual build for a 25K trail race like Marathon du Mont-Blanc 23K, at 4-5 sessions a week. Counted back from a June race that opens the block around late March and runs it March through to June. Coming from a lower base, give yourself longer. With fewer weeks than that the plan compresses. It builds what it can from where you are, protects the work for one long sustained climb, technical descending and a mass field first, and tells you plainly what it had to leave out.
When should I start training for Marathon du Mont-Blanc 23K?
Marathon du Mont-Blanc 23K is usually held in June, and the next edition an athlete could realistically build for is Summer 2027. Count back twelve weeks from whatever date you enter and the block opens around late March, running March through to June. Adaptlete builds backwards from your date, so the whole 25K trail plan lines itself up the moment the date is confirmed. Entry runs on a separate clock (places here are on open entry), and the training deadline is the one you control.
How much climbing is there at Marathon du Mont-Blanc 23K?
A mountain course on trail, with 1,680 m of climbing in it, and in June the weather is genuinely unpredictable, and two editions running rarely feel the same. So the vertical is the event and the distance is how long you are out in it, and the weather is the variable you prepare for, because nobody can plan around it. That combination is what the twelve weeks are built around: one long sustained climb, technical descending and a mass field. The 25K trail race on its own would give you a completely different plan.
What kit do I need for Marathon du Mont-Blanc 23K?
Trail, so the long sessions have to happen on ground like it. Footing, poles, descending and eating while you move are skills, and none of them are learnable on a treadmill in the last two weeks. There is 1,680 m of climbing in it, about 67 m in every kilometer. Over twelve weeks the plan puts the long sessions on ground like it and asks you to use the same pack, poles, shoes and food you intend to use in June. Check the organizers' own mandatory kit list. It is theirs, it changes, and we do not publish it.
What is the start like at Marathon du Mont-Blanc 23K?
A large field means a start pen, a gun time that is not your chip time, and a first mile you do not control. With tens of thousands starters on mountainous trail, the opening miles are the most common place a good 25K trail build gets spent in ten minutes. The plan rehearses the first section at goal effort inside the long session, so the pace you hold in June is one your legs recognize and the crowd did not choose. It keeps the work for one long sustained climb, technical descending and a mass field in the block while it does it.
What if I miss two weeks in the middle of my Marathon du Mont-Blanc 23K build?
Tell the app you were ill, traveling or hurting and it rewrites the rest of the block from where you actually are. Over twelve weeks running March through to June that happens to almost everybody and is the most common reason a 25K trail build falls apart. The rebuild protects the sessions that matter for one long sustained climb, technical descending and a mass field rather than cramming back the ones you missed.
Is this an official Marathon du Mont-Blanc 23K training plan?
No. Adaptlete is an independent training-plan service with no affiliation to the organizers of Marathon du Mont-Blanc 23K, and none is implied. We name the race because the plan is built around what its course, its format and its date ask of you.