What Is the OCC?
OCC stands for Orsières–Champex–Chamonix — the route of the race. It starts in Orsières in Switzerland, climbs through the Val d'Entremont, passes Champex-Lac and Trient, and climbs to the Col de Balme and Tête de Balme before crossing into France via Vallorcine and the Col des Posettes, finishing in the centre of Chamonix during UTMB week each late August — Thursday 27 August in 2026.
It is one of the three Finals races of the UTMB World Series — the annual 50K-category final, sitting alongside the CCC (the 100K final) and UTMB itself (the 100M final).
The 2026 course was redesigned in its upper section. A new route between Col de Balme and Col des Posettes added a new high point at Tête de Balme (2,321m), the old climb to La Flégère was dropped, and the final kilometres into Chamonix changed. The result is 60km with around 3,500m of climbing and a maximum allowed time of 14 hours 30 minutes. Routes can change from year to year with weather and safety, so always check the official race page.
Why is a 60km race the “50K” final? UTMB uses km-effort — distance plus 1km for every 100m of climbing — to compare races of different steepness, and the category names are labels rather than exact distances. At 60km and 3,500m, the OCC works out at about 95 km-effort, but it is designated as the 50K-category final.
That distance-and-climb combination puts the OCC in an interesting physiological sweet spot. In trail races of around 50km, classic engine measures — especially the speed you can reach at VO₂max — are among the strongest predictors of finishing time, although that link weakens as races get longer. On mountain terrain, in our experience, strength, descending skill and fatigue resistance increasingly decide who runs well in the final third.
Because the OCC is a Final, you can't simply enter it. Your place has to be earned through the UTMB World Series system — so this guide covers qualification first, then training.
How to Qualify for the OCC
To enter the OCC lottery you need two things: at least one Running Stone earned in the past 24 months, and a valid UTMB Index in the 20K, 50K, 100K or 100M category.
What Is a Running Stone?
A Running Stone is a ticket into the Finals lottery. You earn stones by finishing UTMB World Series Events or Majors in the 20K, 50K, 100K or 100M categories. Finishing the Finals races themselves does not award stones.
| Category | World Series Event | World Series Major |
|---|---|---|
| 20K | 1 stone | 2 stones |
| 50K | 2 stones | 4 stones |
| 100K | 3 stones | 6 stones |
| 100M | 4 stones | 8 stones |
Majors are the regional flagship events, and they award double: Val d'Aran (Europe), Kodiak (Americas), Chiang Mai (Asia-Pacific) and Ultra-Trail Australia (Oceania).
- Each stone is one chance in the draw — six stones means six entries.
- If you're drawn, your stones are used up and reset to zero.
- If you're not drawn, your stones carry forward — they don't expire.
- At least one stone must have been earned in the past 24 months.
What Is the UTMB Index?
The UTMB Index is a performance score calculated from your results in UTMB World Series and UTMB Index races, held per category (20K, 50K, 100K, 100M). A category becomes valid when you finish a race in it within the past 24 months; once it is active, your results from the past 36 months feed the score. For the OCC, a valid Index in any of the four categories is accepted, and you need it in place when you pre-register.
Direct Qualification
Beyond the lottery, strong performances earn a place in the following year's Final in the same category:
- Top 3 men and women in the 50K, 100K or 100M categories at any UTMB World Series Event.
- Top 10 men and women in each category at a Major.
- Runners who reach a set UTMB Score in a qualifying race.
- The age-group category winners at Majors.
For most runners, though, the path is stones plus lottery.
Your Path, Step by Step
- Finish one or more UTMB World Series races in the 20K–100M categories to earn Running Stones.
- Make sure at least one result gives you a valid UTMB Index (any category from 20K up works for the OCC).
- Pre-register for the OCC in January — each of your stones counts as an entry.
- Drawn? Confirm and pay by the deadline (4 February in 2026) or you lose the place. Not drawn? Your stones carry forward for next year.
- Alternatively, chase a direct slot with a top-3 finish at an Event or a top-10 at a Major.
Plan qualifying races well ahead — travel, cost and entry windows all matter, and popular events sell out early.
Training Strategy for the OCC
A 60km race with 3,500m of climbing has to be trained for on four fronts at once: the aerobic engine, strength and durability, technical terrain skill, and fuelling. Neglect any one and the course finds it.
What to Emphasise
- VO₂max builds your ceiling — in trail races of around 50km, speed at VO₂max is among the best predictors of performance.
- Lactate threshold decides what fraction of that ceiling you can actually sustain. This is our coaching judgement rather than a research finding: for most runners it deserves the larger share of training time.
- Running economy is free speed. Train it on the terrain you'll race on — climbing and descending, not just flat running. Research on whether uphill economy is a separate, independently trainable quality is mixed, so we don't treat it as one.
- Strength — especially quads, glutes, calves and core — is what survives roughly 3,400m of descending. Heavy lifting and plyometrics, especially combined, have the best evidence for improving running economy.
- Fatigue resistance, gut tolerance and recovery quietly decide the final two hours.
Periodisation
Base (3–4 months): volume and easy aerobic hours, hills and trails, light strength work, and early technical skill practice — especially descending confidence.
Build (2–3 months): hold the volume, add threshold and long hill intervals, introduce VO₂max work without overdoing it, add heavy strength and plyometrics plus eccentric-focused work for downhill loading, and start race-simulation days on OCC-like terrain, including back-to-back days.
Peak (3–4 weeks): taper the volume but keep touches of intensity, rehearse race pace on terrain, and finalise fuelling and kit — nothing new after this point.
Race and recovery: execute the plan, then recover properly and review what you learned.
Key Sessions
- VO₂max: the classic 4 × 4 minutes at 90–95% of max heart rate with 3-minute easy jog recoveries is effective and manageable. Keep high-intensity work to roughly a fifth of weekly load or less.
- Threshold: 20–30 minutes continuous at “comfortably hard” — the pace where speech drops to a word or two — or intervals like 3 × 10 minutes. Extend as fitness builds, ideally on rolling ground.
- Long runs: on terrain that resembles the OCC — sustained climbs, technical descents, uneven surfaces. Every few weeks make it a genuinely long mountain day (4–6 hours), and use occasional back-to-back days to train running on tired legs.
- Strength: two sessions a week. Include a heavy block (around 3–6 reps at 80% or more of your one-rep max) and plyometrics — bounding and hops — for economy, plus deliberate eccentric work for durability: controlled downhill repeats and eccentric calf lowering. Lighter 8–12 rep sets have less evidence for improving economy, though they can still help general durability.
- Technique: practise foot placement, rock-hopping and descending lines on real technical ground, and learn to climb efficiently: shorter strides, strong posture, and power-hiking when it's faster than running.
Fuelling and Gut Training
Practise your race fuelling on every long run — the gut adapts to absorbing carbohydrate under stress, but only if you train it. Current guidance for efforts over 2.5 hours is about 90g of carbohydrate per hour. A 2020 study of elite male trail runners (Urdampilleta et al.; 26 enrolled, 20 analysed) found that 120g per hour during a mountain marathon with around 4,000m of climbing limited neuromuscular fatigue and improved recovery of high-intensity running capacity 24 hours later, compared with 90g and 60g per hour. It's a small study of a marathon-length race rather than an ultra, and it only works if your gut tolerates it — which is precisely why it has to be rehearsed. Our full guide on how to fuel an ultra covers targets and an hour-by-hour approach, and do ultra runners really need gels? weighs gels against real food.
An Example Build-Phase Week
- Monday: recovery run + light strength and core.
- Tuesday: threshold — 3 × 12 minutes comfortably hard, 3-minute jog recoveries.
- Wednesday: medium trail run with hills, steady aerobic, plus drills.
- Thursday: VO₂max — 4 × 4 minutes at 90–95% of max heart rate with full warm-up and cool-down.
- Friday: easy run + lower-limb strength (heavy work and plyometrics) and mobility.
- Saturday: long mountain run (3–4 hours) over mixed terrain, final hour progressive.
- Sunday: easy active recovery or rest.
Adjust around fatigue, terrain access and life — the plan serves you, not the other way round.
Race Strategy & Tactics
- Pacing: stay below threshold through the early sections — the race is decided after Col de Balme, not before it.
- Fuelling: start early and stay consistent; never let yourself run empty before reacting.
- Descents: avoid over-braking — it shreds the quads. Pick lines early and let the gradient work for you.
- Conditions: alpine weather and altitude change quickly; have contingency pacing in mind.
- Mental structure: break the course into checkpoint-to-checkpoint segments with micro-goals.
- Cut-offs: know them cold — staying ahead of them is as much a part of the race as speed.
Common Pitfalls
- Chasing VO₂max, neglecting threshold and volume — in our experience the most common imbalance, and it shows up in the final third.
- Under-training strength — you pay for it on the descents into Chamonix.
- Training on roads, racing on mountains — terrain specificity is not optional here.
- Ignoring recovery — accumulated fatigue derails more OCC builds than missed sessions do.
- Race-day experiments — every fuelling and kit choice must be validated in training first.
- Leaving qualification late — stones races sell out, and the January pre-registration window is short (12 days in 2026).
Frequently Asked Questions
What does OCC stand for?
Orsières–Champex–Chamonix — the route of the race, from Orsières in Switzerland to the finish in Chamonix, France. It's the 50K-category final of the UTMB World Series.
How long is the OCC?
The 2026 edition, run on 27 August, was 60km with around 3,500m of climbing, and a maximum allowed time of 14 hours 30 minutes.
Why is a 60km race called the “50K” final?
UTMB's category names are labels, not exact distances. Races are compared using km-effort (distance plus 1km per 100m of climbing); the OCC comes in at about 95 km-effort and is designated as the 50K-category final.
How do I qualify for the OCC?
At least one Running Stone earned in the past 24 months, plus a valid UTMB Index in the 20K, 50K, 100K or 100M category. Pre-register in January (8–19 January in the 2026 cycle). Top-3 finishers at Events and top-10 finishers at Majors can qualify directly for the following year's Final in the same category.
Do I lose my Running Stones if I am not drawn?
No — undrawn stones carry forward to future years. If you are drawn, your stones are used up.
Which UTMB Index do I need for the OCC?
A valid index in any of the 20K, 50K, 100K or 100M categories, in place when you pre-register.
Sources
- UTMB World Series sports system and competition rules: utmb.world/sports-system
- OCC race page: montblanc.utmb.world/races/OCC
- UTMB World Series Majors: utmb.world/UTMB-World-Series-Majors
- iRunFar, 2026 OCC results and course changes: irunfar.com/2026-occ-results
- Urdampilleta et al. (2020), 120 vs 60 and 90 g/h carbohydrate during a trail marathon, Nutrients: PMC7400827
- Coates et al. (2021), Physiological determinants of ultramarathon trail-running performance, Int J Sports Physiol Perform: journals.humankinetics.com
- Llanos-Lagos et al. (2024), strength training and running economy: systematic review with meta-analysis, Sports Medicine: doi:10.1007/s40279-023-01978-y
