Cairns is a tropical race, and tropical humidity is the single biggest fuelling variable in Australian triathlon. Sweat does not evaporate efficiently, core temperature climbs, gastric emptying slows, and the carbohydrate plan you rehearsed in a cool southern winter suddenly feels like too much.
The fix is not less carbohydrate, it is more fluid volume and more sodium alongside the same carbohydrate, delivered in a concentration the gut can move. Practise it in heat before race day.
What the race demands
Distance
1.9km swim, 90km bike, 21.1km run
Conditions
Tropical far north Queensland, warm and very humid
Main risk
Heat slowing gastric emptying and stalling carbohydrate intake
Second risk
Large sodium losses producing cramp and a broken run
Carbohydrate and sodium targets
- Bike leg: 70 to 90g of carbohydrate per hour from a dual-carb source
- Run leg: 60 to 80g of carbohydrate per hour in small frequent doses
- Sodium: 800 to 1,200mg per hour is common in tropical humidity for heavy sweaters
- Fluid: higher than a temperate race, set by your measured sweat rate
HYDRAX CORE delivers 85g of dual-carb fuel and 980mg of sodium per serve, so hitting the numbers above is arithmetic rather than guesswork. HYDRAX PRIMER covers the pre-race window with 29g of carbohydrate and 1,313mg of sodium. Run the free fuelling strategy tool to convert these ranges into your own per-hour numbers.
Rehearse the plan in training, then race it. Order now, ships Australia-wide.
Race week and race day timeline
2 days out
Raise carbohydrate intake, drop fibre and anything unfamiliar.
Race morning, 3 hours out
Rehearsed carbohydrate breakfast at 1 to 2g per kg with sodium in your fluid.
25 to 40 minutes pre-swim
One serve of PRIMER: 29g of carbohydrate and 1,313mg of sodium before the swim blackout.
Bike, 90km
Fuel on a timer from the first 10 minutes, and keep the drink dilute enough that your gut can empty it in the heat.
Run, 21.1km
Keep carbohydrate coming in small doses from the first aid station. The half marathon is won by the athlete who fuelled the bike properly.
Frequently asked questions
How do I fuel a half Ironman in tropical heat?
Keep the carbohydrate target, raise fluid volume and sodium, and dilute the mix slightly so your gut can absorb it while core temperature is high. Start fuelling within the first 10 minutes of the bike and never chase a deficit later.
How much sodium for IRONMAN 70.3 Cairns?
Heavy and salty sweaters often need 800 to 1,200mg per hour in tropical conditions. Test your own sweat rate in heat rather than transferring numbers from a cool-weather race.
Why do I cramp in humid triathlons?
Cramping is multifactorial, but under-replaced sodium combined with high sweat losses and pacing above trained effort is the pattern most athletes report. Plan sodium properly and pace the bike conservatively.
Should I change my nutrition if the race is hotter than expected?
Yes. Keep carbohydrate per hour steady, increase fluid and sodium, and take smaller more frequent doses instead of large slugs, which are harder to empty from the stomach when you are hot.
Keep reading
- Ironman 70.3 nutrition guide
- Full Ironman nutrition guide
- Carbs per hour for Ironman
- Triathlon time calculator
- Measure your sweat rate
- Shop the HYDRAX kit
Disclaimer: This page is general information for healthy adult athletes and is not medical, dietetic or coaching advice. Individual carbohydrate, fluid and sodium requirements vary with body weight, sweat rate, conditions and health status. Speak with your doctor, sports physician or an accredited sports dietitian before changing your nutrition or supplement routine, rehearse any fuelling plan in training before race day, and always follow the directions and warnings on the product label.