Long-course triathlon is as much a fuelling problem as a fitness problem. The run leg exposes every under-fed hour on the bike — regardless of how strong your Thresholds look on paper.
For most age-group 70.3 athletes the race lasts 4–6 hours: long enough to deplete glycogen, short enough that many still under-fuel. Carb targets in WattX scale with weight, predicted split, and Race Pacing Targets — a harder bike raises oxidation and tightens the margin.
Carbs
Why Carbs Matter at 70.3
At planned race effort you store roughly 90–120 minutes of glycogen. A 70.3 lasts far longer. Without exogenous carbohydrate, pace collapses — often suddenly. Fuel early; waiting until you feel hungry means you are already behind.
Current science supports 60–90 g carbohydrate per hour during sustained endurance when the gut is trained. The upper band needs a 2:1 glucose:fructose blend so two intestinal transporters can work in parallel. Single-source glucose alone often caps absorption around 60 g/h and increases GI distress.
Upper band needs 2:1 glucose:fructose. Front-load on the bike; simplify on the run.
By leg
Fuelling by Leg
No mid-race fuel
70–150 g carbs 2–3 h pre-start. Familiar, low fibre. Swim is 20–35 min for most.
Main fuelling window
Train 70–90 g/h when tolerated. WattX defaults: 60 g/h (70.3) · 75 g/h (IM).
Simpler formats
Gels every 25–30 min from km 1. Defaults: 45 g/h (70.3) · 55 g/h (IM).
The Nutrition Strategy tool uses conservative per-distance defaults from your weight, predicted split, and temperature — train higher in practice, race from the playbook.
Hydration
Hydration and Sodium
Do not rely on thirst alone in competition.
Pacing link
Linking Pacing and Fuel
Harder bike pacing increases carb oxidation. Under-fuel on the bike and the run pays regardless of fitness.
Set Race Pacing Targets in the Race Simulator — the predicted split feeds straight into Nutrition Strategy.
Your numbers
Calculating Your Numbers
Carbohydrate needs scale with weight, pace relative to your CSS, FTP, and FT, and conditions. WattX totals swim, bike, and run carbs, fluid, and sodium from your profile — and refreshes when simulator time or distance changes.