The wall is not a mystery. It is glycogen depletion arriving on schedule, at exactly the point in the race that the fuel plan you did not build in advance can no longer save. Most marathoners describe the last 10km as an emotional battle. Physiologically, it is almost always an accounting problem.
You store roughly 500g of glycogen when fully loaded. A 70kg runner at marathon pace burns through 350 to 500g of glycogen across the race. The maths only works if you top up as you go. This is what a marathon fuelling plan is for.
Carb intake by finish time
| Finish Time | Carb Target | Sodium Target | HYDRAX Approach |
|---|---|---|---|
| Sub 3:00 | 60-90g/hr | 500-800mg/hr | PRIMER pre + carried flask of concentrated CORE, sipped every 3-4km |
| 3:00 - 3:30 | 55-80g/hr | 500-750mg/hr | PRIMER pre + flask of CORE, sipped every 3-4km |
| 3:30 - 4:00 | 45-70g/hr | 400-700mg/hr | PRIMER pre + dilute CORE at aid stations from 30 min |
| 4:00 - 5:00 | 30-60g/hr | 300-600mg/hr | PRIMER pre + small sips of CORE from 30-40 min |
| 5:00+ | 30-45g/hr | 300-500mg/hr | PRIMER pre + regular small sips of dilute CORE throughout |
For a deeper look at per-hour targets in marathon-distance running, see our breakdown of how many carbs per hour a marathon actually requires.
The 48 hours before
2 days out: Begin structured carb loading at 7 to 10g of carbohydrate per kg bodyweight per day. Reduce fibre, fat and protein moderately to make room for carbs. Full protocol in carb loading the day before your race.
The night before: Familiar high-carb dinner. Pasta, rice, potato. No alcohol. No new foods. Water with electrolytes throughout the evening.
Race morning, 3 to 4 hours out: 1 to 2g carb per kg bodyweight. Oats with banana and honey, white toast with jam, rice with eggs. Familiar food only.
25 to 40 minutes before the gun: One serve of HYDRAX PRIMER in 400 to 500ml water. Sodium pre-load and dual-carb top-up before the first stride.
During the race: small sips, right on time
Marathon fuelling is a rhythm problem, not a volume problem. The runners who blow up are usually the ones who fuel reactively - a big gulp at 25km when it already feels bad - rather than proactively.
Start fuelling by 30 to 40 minutes. Do not wait for the feeling of low. It is already too late by then.
Small, frequent doses. A handheld flask with a serve of HYDRAX CORE in 400 to 500ml water, sipped every 3 to 4km, delivers carbs and sodium in a rhythm the gut can absorb without overwhelming it. The dual-carb formulation (2:1 maltodextrin-to-fructose) uses two intestinal transport pathways simultaneously, lifting absorption capacity to 90 to 120g per hour. See the science in why dual-carbohydrate transporters matter.
Sodium in the mix. Do not rely on aid station water. Most on-course drinks provide 100 to 230mg sodium per 500ml - a fraction of what a moderate sweater loses. HYDRAX CORE delivers 980mg per serve.
Tune the plan to your experience
The finish-time ranges above are the working envelope. Where you sit inside them depends on how much you have rehearsed high-rate fuelling on long runs. Do not race a number you have not trained. Build tolerance progressively with our gut training guide.
| Experience | Realistic carbs/hr |
|---|---|
| Beginner (first marathon) | 30-45g |
| Intermediate | 45-75g |
| Experienced (rehearsed high-carb gut) | 75-100g |
Aid stations: know them, don't rely on them
Read the race information the week before. Know which brand of sports drink and gel is on course, and at which kilometre markers. That is your plan B.
Plan A is self-sufficiency. Aid stations run out, cups spill, and on-course brands are often not what you trained with. Carry a handheld or soft flask with HYDRAX CORE so you can hit your carb and sodium target using only products you have rehearsed.
Pro tip: the concentrated soft flask
Train long runs with a soft flask carrying a concentrated serve of HYDRAX CORE - one full serve in 150 to 250ml of water. Sip every 2 to 3km and top up with plain water at aid stations. You get a full hour of carbs and sodium in your hand, independent of aid station timing or brand.
Build a plan tailored to you
This guide is the framework. For a plan built to your body weight, pace and sweat rate, use the HYDRAX Fuelling Strategy Engine, estimate losses with the sweat rate estimator, structure the 48 hours before with our carb loading protocol, and dial pace with the marathon pace calculator.
A marathon rewards a rehearsed plan. Fuel it with PRIMER and CORE. Order now, ships Australia-wide.
Common marathon fuelling mistakes
1. Skipping fuel in the first 30 minutes. You feel strong. You do not need it yet. By the time you do, you are behind.
2. Under-fuelling in training. Marathon fuel is a rehearsed skill. If you have never taken 60g/hr on a long run, do not attempt it on race day.
3. Ignoring sodium. Cramps in the last 8km are usually sodium, not carbs. Learn your sweat rate with the sweat rate estimator.
4. Trying something new on race day. The gel a friend recommended two weeks out is a bad bet. Race-day products should have logged at least 3 race-pace sessions in training.
5. Water-only pacing. Plain water dilutes plasma sodium and increases hyponatraemia risk on longer efforts, without providing carbohydrate. Water + electrolyte + carb is the baseline, not the upgrade.
Related resources
- Carbs per hour for marathon runners
- Endurance fuel for runners
- Carb loading in the 48 hours before
- Marathon pace calculator
- Fuelling Strategy Engine
- Gold Coast Marathon fuelling plan
- Sydney Marathon fuelling plan
- Melbourne Marathon fuelling plan
- Brisbane Marathon fuelling plan
- Perth Marathon fuelling plan
A marathon rewards a rehearsed plan. Fuel it with PRIMER and CORE. Order now, ships Australia-wide.
Frequently Asked Questions
How many carbs per hour do I need for a marathon?
For sub-3-hour runners, target 60 to 90g of carbohydrate per hour using a dual-carb source. For 3 to 4 hour finishers, 45 to 75g per hour is realistic. For 4 to 5 hour finishers, 30 to 60g per hour is achievable with a rehearsed gut. HYDRAX CORE at 85g per serve makes hitting these numbers straightforward.
When should I start fuelling during a marathon?
Start fuelling by the 30 to 40 minute mark, well before you feel low. Once glycogen has dropped it is very hard to catch back up on the run. Small, regular carbohydrate intake from early keeps blood glucose stable through the second half.
How much sodium do I need during a marathon?
Target 300 to 800mg of sodium per hour depending on sweat rate and conditions. HYDRAX CORE delivers 980mg per serve so even at moderate volumes you cover most sodium needs. Use our sweat rate estimator to personalise the number.
Do I need HYDRAX PRIMER before a marathon?
Yes, especially for warm-weather races or hard efforts. One serve of PRIMER 25 to 40 minutes before the gun delivers 29g of dual-carb fuel and 1,313mg of sodium, expanding plasma volume before you sweat a drop.
Gels or drink mix for a marathon?
A dilute drink mix such as HYDRAX CORE tends to be gentler on the gut than a chain of gels, provides sodium alongside carbs, and delivers a more even blood glucose profile. Read our full comparison of drink mix versus gels for the physiology.
How do I avoid hitting the wall at 30km?
The wall is glycogen depletion. Two levers prevent it: carb load in the 48 hours before, and fuel with 45 to 90g per hour from the 30-minute mark. Miss both and 32km hurts. Hit both and it does not.
42.2 kilometres. Fuel on the clock, not the feeling.
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.