A full Ironman is a nutrition race with a swim, bike and run attached. Over eight to fifteen hours you cannot store what you need in advance, so the day is decided by how many grams of carbohydrate and milligrams of sodium you can actually absorb per hour, every hour.
Cairns raises the difficulty because tropical heat and humidity slow gastric emptying at exactly the point you need intake to be highest. The athletes who run well here are the ones who practised hot fuelling, not the ones who hoped for a cool day.
What the race demands
Distance
3.8km swim, 180km bike, 42.2km run
Conditions
Tropical far north Queensland, hot and humid with a coastal bike leg
Main risk
Heat suppressing intake and creating an unrecoverable deficit
Second risk
Very high sodium losses over a long day
Carbohydrate and sodium targets
- Bike leg: 80 to 120g of carbohydrate per hour from a dual-carb source if your gut is trained for it
- Run leg: 60 to 90g of carbohydrate per hour in small frequent doses
- Sodium: 700 to 1,200mg per hour, higher again for salty and heavy sweaters
- Fluid: guided by your measured sweat rate, tracked hour by hour
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
3 days out
Carb load toward 8 to 12g per kg per day and cut fibre well before race morning.
Race morning, 3 hours out
Rehearsed carbohydrate breakfast at 2g per kg with sodium in your fluid.
25 to 40 minutes pre-swim
One serve of PRIMER for 29g of carbohydrate and 1,313mg of sodium before a 3.8km fuelling blackout.
Bike, 180km
Fuel on a strict clock from the first 15 minutes. Slightly more dilute in the heat so the gut keeps absorbing.
Run, 42.2km
Small doses at every aid station. Nothing new, nothing large, and no skipping when you feel fine.
Frequently asked questions
How many carbs per hour for a full Ironman?
Well-trained athletes with gut training target 80 to 120g of carbohydrate per hour on the bike and 60 to 90g per hour on the run. The correct number is the highest rate you have rehearsed without gut distress, not the highest number you have read.
How much sodium do I need at IRONMAN Cairns?
Tropical conditions push many athletes to 700 to 1,200mg of sodium per hour, and heavy salty sweaters higher again. Measure your sweat rate in heat before race day.
What should I eat the week of an Ironman?
Increase carbohydrate through the final three days toward 8 to 12g per kg per day, reduce fibre as race day approaches, and keep food familiar. Race week is for repetition, not experiments.
Why do Ironman athletes blow up on the marathon?
The usual causes are a carbohydrate deficit built on the bike, sodium replacement below sweat losses, and riding above the effort trained for. All three are planning problems, not toughness problems.
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.