Preparing for the Diagonale des Fous: Race Plan, Segments and Strategy

From Saint-Pierre to Saint-Denis, at night, across the La Réunion National Park, a UNESCO World Heritage Site. The Diagonale des Fous is not just one of the most demanding trail races in the world — it's an inner crossing as much as a geographical one. And like every event that pushes limits, it's prepared segment by segment.

What the Diagonale des Fous really is

The Diagonale des Fous is an extreme trail race held on La Réunion that embodies the spirit of adventure, endurance and challenge. Every year, runners from around the world gather to take on this bold challenge.

But behind that sober description lies a much more demanding reality. The course crosses the heart of the island, from lush forests to steep rocky ridges, and tests the physical and mental resilience of every participant. The start is at night, in Saint-Pierre, in the south of the island. The finish is in Saint-Denis, in the north — a true diagonal drawn across the three legendary cirques: Cilaos, Mafate and Salazie.

For the 2026 edition, the race takes place on 15 October over a course of 180.81 km with 10,191 m of elevation gain. The maximum altitude exceeds 2,477 m, and the minimum altitude barely reaches sea level at the finish.

The course profile: understand before you run

The Diagonale is not a uniform race. It breaks down into clearly distinct phases, each with its own logic of effort.

Phase 1 — The climb to the highlands (km 0 to 45)

The start takes place at night from Ravine Blanche, by the sea. The first major aid station is at Domaine Vidot at km 14, after 672 m of D+ from the start. The challenge of this phase: managing the start-line excitement, the darkness, and the gradual climb to the island's highlands without burning through your reserves too early.

Notre-Dame-de-la-Paix comes at km 33, at 1,686 m altitude, with hot food and support. It's the first big checkpoint after 2,148 m of cumulative D+. Most runners pass through at sunrise — a transition moment not to be neglected for nutrition and temperature management.

Le Nez de Bœuf, at km 45 at 2,023 m altitude, is a key point: 2,798 m of cumulative D+ since the start. This is where the race takes on a new face — the cirques open up in front of you.

Phase 2 — The volcano and Mafate (km 45 to 80)

Passing the Mare à Boue at km 55 marks the start of the wild heart of the race, with a doctor, hot food and rescue available. This area, around the volcano and its surroundings, is often windy and can be misty — conditions can change quickly here.

The Mafate cirque is one of the most iconic and demanding parts of the race. Reachable only on foot or by helicopter, this cirque with no roads or cars imposes its own logic: ravines to cross, brutal climbs, technical descents on narrow trails. Passing through Hell-Bourg at km 80, at 995 m altitude, marks the first life base of the race — supporter access, massage, doctor, hot food. This is often where runners take their first real recovery break.

Phase 3 — Cilaos and the ridges (km 80 to 130)

After Hell-Bourg, the race enters its most mentally demanding phase. The Cilaos cirque, with its dizzying ramparts, demands constant and brutal changes in altitude. Cilaos-Stade, around km 76, is the second major life base — village, car access, hot drinks, massage, doctor. Many runners experience their most intense crisis here.

The ridges that follow Cilaos are often where a race is abandoned or reborn. Cold, wind and altitude combined with more than 100 km in the legs test even the best-prepared runners.

Phase 4 — The descent to Saint-Denis (km 130 to 180)

The final descent to Saint-Denis is deceptive. It's not a simple downhill — it still includes several significant climbs and technical sections. The Colorado, around km 171, offers one last aid station before the finish. The final kilometres to Saint-Denis, a gradual descent towards the sea, are often run with a mix of total exhaustion and intense emotion.

Race strategy: the keys to not blowing up

1. Managing the night start

The Diagonale starts at night. The start-line excitement, the electric atmosphere of Saint-Pierre, the cool night air — everything pushes you to go out too fast. It's the most classic and most fatal mistake on this race. The first 33 km to Notre-Dame-de-la-Paix should be run at strict fundamental endurance pace, with rigorous heart-rate control on the climbs.

2. Handling the heat of the first day

Unlike other mountain ultras, the Diagonale begins in a tropical environment. The heat and humidity of the first day — between the start and the climb to the highlands — represent a thermal stress that many runners from mainland France underestimate. Hydration and sodium intake are critical from the very first kilometres.

3. Taking care at the life bases

Two major life bases punctuate the race: Hell-Bourg and Cilaos. These stops are investments, not time wasted. Eating hot food, changing if needed, taking 20 to 30 minutes of recovery at Hell-Bourg can save several hours in the final stretch. Runners who skip the life bases to "save time" often pay for it dearly in the last 50 kilometres.

4. Anticipating weather changes at altitude

Runners must stay alert to climate variations that can turn the course into an even more formidable challenge. On ridges above 2,000 m, the weather can change in a matter of minutes. Windproof jacket, emergency blanket and a warm layer are not optional — they are vital.

5. The fatigue factor on the Diagonale

The Diagonale is the perfect example of a race where the fatigue factor plays a decisive role. Over 180 km and 10,000 m of D+, it is physically impossible to maintain the same pace from start to finish. Segly data on Diagonale plans show fatigue factors typically between 30 and 50% for advanced-level runners — meaning the final segments take 30 to 50% longer than the first ones, at equivalent level.

Understanding this phenomenon before the race lets you start with deliberate restraint over the first 60 kilometres, and save energy for the decisive phases around Cilaos and the ridges.

Key points of the course to know by heart

Notre-Dame-de-la-Paix (km 33) — First big checkpoint. Often reached at sunrise. Make the most of the dawn light and the hot food. Resist the urge to speed up because "you're feeling good".

Nez de Bœuf (km 45) — The turning point into the wild world. Check your feet, your food reserves, and your night gear if you're keeping to the planned pace.

Hell-Bourg (km 80) — Life base 1 — The first big moment of truth. Eat properly, not just nibble. If a blister starts to cause trouble, this is where to deal with it, not 40 km later.

Cilaos (km 76–130 depending on route) — Life base 2 — The Cilaos cirque is mentally the hardest part of the race. Many runners hit their night low here. Plan a clear mental strategy for this phase — music, a mantra, an intermediate goal.

Colorado (km 171) — Last aid station before the finish. About 10 km left. Manage the urge to give everything too early on this final stretch, which remains technical.

Preparing your Diagonale race plan with Segly

The Diagonale des Fous is available in Segly with the official GPX and a segmentation based on the real aid stations. By entering your ITRA, UTMB Index or BeTrail score, Segly calculates for each segment:

• The estimated time, taking into account your real level and the progressive fatigue factor
• The actual passing time at each aid station (22:00 start from Saint-Pierre)
• The forecast weather hour by hour along the course
• Nutrition and gear recommendations suited to the distance and conditions

A Diagonale race plan can't be generated by improvising. It's a race document you consult before the start, memorise at the key points, and that helps you keep a clear head when your body tells you to quit at 3 a.m. somewhere in the Cilaos ramparts.

The Diagonale des Fous is not only a challenge against distance but also against changing weather, difficult terrain and variable altitude. Better to tackle it with a plan.

The Diagonale des Fous is already ready in Segly — official GPX loaded, segmentation aligned with the real aid stations. Select it directly from the plan builder, enter your level, and generate your split times aid station by aid station in 2 minutes.