IRONMAN World Championship (Kona)
The most prestigious endurance event on earth. Lava fields, ocean humidity, headwinds across the Queen K Highway. Heat strain defines the day.
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
75-92°F · high humidity
Climate
hot + humid
Humidity
high
Cutoff
17 hours
Why This Race Is Hard For Sodium
The Cumulative Deficit Window
Kona is the sodium calculator stress test. Trade-wind heat plus high humidity means sweat does not evaporate efficiently, so cooling demands a higher sweat rate for the same workload. The bike leg crosses the Queen K Highway lava fields where radiant heat off black rock pushes apparent temperature 10-15F above ambient. The marathon back half on Alii Drive is where the famous Kona DNFs happen, almost always tracing back to cumulative sodium and fluid deficit from the bike leg. Pro and age-group winners consistently log sodium intake in the 1200 to 1800 mg per hour range across the bike.
Key Considerations
- Plan the bike leg sodium intake conservatively high. Most Kona DNFs trace back to under-fueling sodium on the bike, not the run.
- Humidity blunts evaporative cooling. Sweat rates in Kona run 20-30% higher than the same effort in dry heat.
- Pre-race sodium loading is non-negotiable. Add 1500-2000 mg sodium in the 24 hours before the start.
- The Energy Lab on the run course (mile 16-20) is the highest cramping window. Pre-dose 600 mg sodium at the mile 14 aid station.
Plan the five systems
Free Tools, Pre-Filled For IM Kona
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 IM Kona conditions.
Carb fueling
Hourly carb targets and a fuel menu calibrated to your weight and the IM Kona duration.
Heat protocol
10-14 day adaptation plan if you're racing into humidity.
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 IM Kona timing.
Your IM Kona Plan,
Built From Real Data.
Pro unlocks: actual sodium and fluid intake data from age-group winners and pros, your acclimation index from Strava heat-week training, and a transition-by-transition (swim out, bike on, bike off, run on) sodium and fluid plan calibrated to Kona Queen K conditions.
- 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 IM Kona
How much sodium do Kona finishers typically take per hour?
Bike leg averages 900 to 1400 mg per hour for the front of the age-group field. Run leg drops to 600 to 900 mg per hour because absorption rate is lower under running impact. Total race sodium for a 10-hour finisher typically lands between 9,000 and 14,000 mg.
Why does Kona heat feel worse than other hot races?
Trade wind humidity. Most hot triathlons (Texas, Florida) have similar air temperatures but lower humidity, allowing evaporative cooling to keep core temperature manageable. Kona humidity blocks evaporation; sweat drips off rather than cooling you, so the same effort produces more heat strain.
Should I lower sodium intake on the run because of GI risk?
Slightly. Run-leg sodium intake is typically 60-75% of bike-leg intake due to lower absorption rates under impact. Switch from liquid electrolyte to capsules with water at the mile 13 aid station. Pre-loading on the bike makes the run-leg deficit more manageable.