Most Ironman 70.3 races are not lost on the swim. They are not lost on the bike. They are lost in the second half of the run, when the athlete finally pays for a fuelling plan that was under-cooked, ad hoc, or built around whatever was on the aid station table.
A 70.3 is a 4 to 6 hour race for most age groupers. That puts it squarely in the window where glycogen depletion and sodium loss are the two biggest predictors of finish time. Get those two right and everything else in your race plan gets easier.
What a 70.3 actually demands from your fuel plan
A half Ironman is 1.9km of swim, 90km of bike and 21.1km of run. For a 5-hour finisher, you are burning somewhere around 3,000 to 4,000 kilocalories on the course. Even a fully carb-loaded athlete stores only around 500 to 600g of muscle and liver glycogen. Do the maths and you have a large gap that has to come from what you take in during the race.
The two levers that actually move outcome:
- Carbohydrates per hour - dictates how long you can sustain race pace before glycogen depletion starts pulling watts and pace out of you.
- Sodium per hour - dictates whether cramping, cognitive fog and pace drift start showing up in the back half of the run.
The rest - caffeine, gels, aid station Coke - is optional and highly individual. Carbs and sodium are not.
Race morning: the 3 hours before the swim
3 to 4 hours before start: A familiar high-carb breakfast at 1 to 2g of carbohydrate per kg bodyweight. Oats with banana and honey, white toast with jam, or rice with eggs. Familiar food only. Race day is not the day to try something new.
25 to 40 minutes before your wave: One serve of HYDRAX PRIMER in 400 to 500ml water. 29g of dual-carb fuel, 1,313mg of sodium, no stimulants. This is the pre-race window that most athletes skip and then wonder why they feel flat on the bike. Read our deep-dive on how sodium expands blood plasma volume before the effort begins.
Avoid caffeine spikes over 3mg/kg in the 60 minutes pre-race unless you have practised it. GI risk outweighs marginal alertness benefit.
The bike leg: where the race is won or lost
The bike is your fuelling leg. It is the only part of the race where you can comfortably take on carbohydrate at high rates. What you do here decides what your run looks like.
Target: 70 to 90g of carbohydrate per hour, starting within the first 15 minutes on the bike. Well-trained athletes with a rehearsed gut can push 90 to 120g per hour. Do not attempt this without training it first. See our full guide on gut training for endurance fuelling.
The reason for the dual-carb requirement is physiological, not marketing. A single carbohydrate source saturates the SGLT1 intestinal transporter at around 60g per hour. Adding fructose activates GLUT5, a separate transporter, lifting total absorption capacity to 90 to 120g per hour. This is exactly the mechanism HYDRAX CORE is built around at a 2:1 maltodextrin-to-fructose ratio. Full breakdown in why dual-carbohydrate transporters matter.
Sodium target: 700 to 1,000mg per hour on the bike in Australian conditions. Two scoops of HYDRAX CORE per bottle delivers 980mg of sodium alongside 85g of carbs. Two well-timed bottles per hour and you are hitting both targets simultaneously.
Your 70.3 fuel plan at a glance
| Race Segment | Carb Target | Sodium Target | HYDRAX Protocol |
|---|---|---|---|
| 25-40 min pre-swim | 29g | 1,313mg | 1 serve PRIMER in 400-500ml |
| Bike hour 1 | 70-90g | 700-1000mg | 1 bottle CORE (2 scoops in 600-750ml) |
| Bike hour 2 | 70-90g | 700-1000mg | 1 bottle CORE |
| Bike hour 3 | 70-90g | 700-1000mg | 1 bottle CORE |
| Run 21.1km | 30-60g/hr | 500-800mg/hr | Dilute CORE if tolerated; small sips at aid stations |
Tune the plan to your experience
The ranges above are the working envelope. Where you sit inside them depends on how much you have rehearsed high-rate fuelling in training. Do not race a number you have not trained. Build tolerance progressively with our gut training guide.
| Experience | Bike carbs/hr | Run carbs/hr |
|---|---|---|
| Beginner (first 70.3) | 60-80g | 30-45g |
| Intermediate (multiple 70.3s) | 80-100g | 45-70g |
| Experienced (rehearsed high-carb gut) | 100-120g | 70-100g |
Aid stations: know them, don't rely on them
Read the athlete guide the week before. Know exactly which brand of sports drink, gel and food is on course, and at which kilometre markers. That is your plan B, not your plan A.
Plan A is self-sufficiency. Aid stations run out, hand-ups get missed, on-course drink is diluted inconsistently between stations, and race-day brands can differ from what you trained with. Carry enough HYDRAX CORE in bike bottles and special-needs to hit your carb and sodium target end-to-end without touching an aid station bottle you have not tested.
Pro tip: the T2 soft flask
Train the run leg with a soft flask carrying a concentrated serve of HYDRAX CORE - one full serve dissolved in 150 to 250ml of water. On race day, stash the same pre-made flask in your T2 bag. You clip it to your race belt out of transition and it delivers a full hour of carbs and sodium without depending on aid station volume or timing.
It is the single highest-yield run-fuelling trick most 70.3 athletes never rehearse. Practise it on your long bricks so the concentration, temperature and mouthfeel are familiar.
Build a plan tailored to you
This guide is the framework. For a plan built to your body weight, sweat rate, race course and finish target, use the HYDRAX Fuelling Strategy Engine and estimate your losses with the sweat rate estimator.
Build your 70.3 race-day fuel plan around PRIMER and CORE. Order now, ships Australia-wide.
The run: hold pace, do not chase carbs
The run leg is where most 70.3s unravel. Fuelling on the run is harder than on the bike because your gut motility slows under running impact. Attempting to hit 90g per hour on the run is a recipe for GI distress in most athletes.
Realistic run target: 30 to 60g of carbohydrate per hour, delivered in small, frequent doses. A dilute serve of HYDRAX CORE in a handheld or on-course water, sipped every 2 to 3km, works well. Small sips beat large gulps every time.
If your stomach is uncooperative, drop concentration before you drop volume. Water and sodium keep working even when high-carb intake is off the table.
Read our breakdown of drink mix versus gels for the physiological reason a diluted drink mix outperforms a chain of gels on the run leg.
Common 70.3 fuelling mistakes
1. Under-fuelling the first bike hour. Athletes save fuel for later. There is no "later" in glycogen accounting. Start fuelling within 15 minutes on the bike.
2. Chasing aid station variety. Cola, gels, salt tabs, bananas all together. You are not a compost bin. Pick a plan, rehearse it, execute it.
3. Under-doing sodium. Most standard sports drinks provide 100 to 230mg sodium per 500ml. That replaces about 15% of an average sweat rate. Learn your rate with our sweat rate estimator, then match intake to loss.
4. Trying something new on race day. Every product used on race day should have logged at least 3 race-pace training sessions in advance.
5. Ignoring the pre-race window. One serve of PRIMER 25 to 40 minutes out is one of the highest-yield decisions on race morning.
Related resources
- Full Ironman nutrition plan
- IRONMAN 70.3 Sunshine Coast fuelling plan
- IRONMAN 70.3 Cairns fuelling plan
- IRONMAN 70.3 Busselton fuelling plan
- Noosa Triathlon fuelling plan
- Marathon fuelling strategy
- Carbs per hour for Ironman-distance events
- How much sodium endurance athletes actually need
- Fuelling Strategy Engine
Build your 70.3 race-day fuel plan around PRIMER and CORE. Order now, ships Australia-wide.
Frequently Asked Questions
How many carbs per hour should I take during a 70.3?
For most age group athletes finishing between 4 and 6 hours, target 60 to 90g of carbohydrate per hour, using a dual-carb source such as HYDRAX CORE. Well-trained athletes with a rehearsed gut can push toward 90 to 120g per hour on the bike. See our per-hour breakdown for Ironman-distance events for a full protocol.
When should I start fuelling on the bike leg?
Start within the first 15 minutes of the bike. Do not wait until you feel hungry or flat. Sip HYDRAX CORE steadily from the moment you clip in and aim to hit your carb target within the first hour.
How much sodium do I need for a 70.3?
In hot Australian conditions, sodium losses can exceed 1,000mg per litre of sweat. HYDRAX PRIMER delivers 1,313mg of sodium before the swim, and HYDRAX CORE provides 980mg per serve during the race. That combination keeps most athletes ahead of losses. Read the full guide on how much sodium endurance athletes actually need.
Should I take HYDRAX PRIMER before the swim?
Yes. Take one serve of PRIMER in 400 to 500ml of water 25 to 40 minutes before your wave start. It pre-loads plasma volume with sodium and tops up blood glucose with 29g of dual-carb fuel before the first stroke.
How do I avoid GI distress on the run leg?
Two rules: rehearse your race-day fuel plan in training, and do not introduce anything new on race day. Stick to isotonic HYDRAX CORE during the bike, which sits comfortably in the gut at race pace, and reduce carb concentration only if your stomach signals stress on the run.
Is HYDRAX suitable for full Ironman as well as 70.3?
Yes. HYDRAX CORE is engineered for sessions and races over 60 minutes, including full Ironman. For a longer-distance protocol, see our dedicated full Ironman nutrition plan.
4 to 6 hours of racing. Fuel it like it matters.
Disclaimer: This guide is general educational information based on endurance sports science, not medical, dietetic or coaching advice. Individual responses to carbohydrate and sodium intake vary. Consult a qualified sports dietitian, doctor or coach before making changes to your race-day nutrition, and always follow the mandatory warnings and directions on the product packaging.