UTMB
The Ultra-Trail du Mont-Blanc. 106 miles, 32,800 feet of climbing, three countries, one of the deepest ultra fields in the world.
Course Profile
Where The Sodium Math Bends
Schematic profile · Cramping windows tend to cluster around major climbs and the descents that follow them
Climate Window
30-75°F · moderate humidity
Climate
mild
Humidity
moderate
Cutoff
46h 30m
Why This Race Is Hard For Sodium
The Cumulative Deficit Window
UTMB combines alpine altitude swings (Chamonix at 3,400 ft, Col du Bonhomme at 7,400 ft), variable mountain weather, and a 30+ hour effort. The temperature can swing 40F across a single day from valley afternoons to col-top nights. Sodium planning has to flex across the climate spectrum. The combination of European drink-mix culture (less standardized than US races), language barriers at aid stations, and unfamiliar foods makes self-supplied sodium more critical than at LOTOJA or Leadville. Most US athletes underestimate the second-night cold descent into Champex where hypothermia plus sodium deficit drops a meaningful percentage of the field.
Key Considerations
- Carry self-supplied sodium capsules; do not rely on European aid station electrolyte mixes which vary widely in formulation.
- Col descents at night are the cramping windows. Pre-dose 600 mg sodium at each col summit.
- The Courmayeur to La Fouly stretch (Italy to Switzerland) is the most common drop window; sodium and fluid deficit from the previous 50 miles catches up here.
- Heat-day variant: in years with afternoon temperatures above 80F in the valleys, treat the lower segments like a hot race even if cols stay cool.
Plan the five systems
Free Tools, Pre-Filled For UTMB
Tap any tool. We pre-load your event, climate, and sweat profile. Adjust your weight and finish target and the plan generates instantly.
Sodium plan
Per-hour sodium and fluid targets for UTMB conditions.
Carb fueling
Hourly carb targets and a fuel menu calibrated to your weight and the UTMB duration.
Heat protocol
10-14 day adaptation plan if you're racing into a warmer climate.
Hydration audit
Weigh-in test that converts a 60-minute training session into a measured sweat rate.
Caffeine timing
Pre-race dose, mid-race top-ups, and race-week taper protocol for UTMB timing.
Your UTMB Plan,
Built From Real Data.
Pro unlocks: sodium and fluid data from UTMB top-100 finishers, your alpine ascent history from Strava (rides and runs with significant vertical), and a col-by-col schedule for the Mont-Blanc loop with weather-day variants.
- Measured sweat rate from a Strava ride or weigh-in test
- Per-leg sodium schedule keyed to the course profile
- Multi-event race calendar across the season
- Post-race feedback capture so the next plan is sharper
Per race
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Common Questions
About UTMB
Are European drink mixes compatible with my sodium plan?
Generally not. Most European aid station mixes are calibrated to French and Italian athletes, who tend toward the average to low sweat sodium profile. Salty sweaters and very-salty sweaters should self-supply electrolyte capsules and use the aid station mix as fluid plus carbohydrate, not as the primary sodium source.
How do I plan sodium across multiple alpine cols?
Treat each col as a discrete segment. Pre-dose 600 mg sodium 30 minutes before the climb base. Maintain normal hourly intake during the climb. Pre-dose another 300 mg at the summit before the descent. Most cramping happens in the first 20 minutes of the descent due to neuromuscular fatigue, not the climb itself.
Does altitude change my UTMB sodium needs?
Less than Leadville because UTMB max elevation is 8,300 ft versus Leadville above 12,000 ft. Plan a 3-5% bump over your calculator output rather than 5-10%.