Master your marathon fuelling early and you give yourself a far better chance of avoiding the wall. Get your carbs, fluids and sodium right, and the second half of the race becomes a problem to manage rather than a slow shuffle to the finish.
The Short Version (TL;DR):
To avoid "the wall," you need a simple three-pillar system. Aim for 30–60g of carbohydrates per hour (using gels or sports drinks), 400–800ml of fluids, and 300–800mg of sodium depending on your sweat rate. Start fuelling within the first 45 minutes of the race. Don’t wait until you’re hungry or thirsty; by then, it’s usually too late to recover.
The fueling trap
Most runners treat race-day nutrition as an afterthought, something to "figure out" in the final fortnight of training. They follow a generic plan they found online, only to find their stomach doing somersaults at mile 18.
I’ve seen it hundreds of times. You’ve done the hard miles, your legs feel strong, and your pacing is spot on. Then, the energy levels plummet. You aren't "hitting a wall" because you lacked fitness; you’re hitting it because you ran out of petrol. Marathon success is 50% physical preparation and 50% energy management.
At PFM Coaching, I work with athletes to build these habits into every long run, ensuring that on race day, the "system" is as robust as the legs.
The Engine: Why Carbs Are King
Your body has a limited store of glycogen (stored carbohydrates) in the muscles and liver. For most of us, that store lasts about 90 to 120 minutes at marathon intensity. If your race takes four hours, you have a massive energy gap to fill.
The Golden Rule: 30–60g of Carbohydrates Per Hour.
This is the sweet spot for most marathoners. If you are a faster, more experienced athlete who has "trained their gut," you might push toward 90g, but for 95% of runners, 60g is the target.
- 1 Standard Gel: ~20–25g of carbs.
- 500ml Sports Drink: ~30g of carbs.
- A handful of chews: ~15–20g of carbs.
To hit your target, you’re looking at one gel every 30 to 45 minutes, perhaps supplemented by small sips of an electrolyte drink.
Hydration and Salt: The Cooling System
Think of hydration and sodium as your body's radiator fluid. If you run low, the engine overheats, and your heart has to work significantly harder to pump blood to your working muscles.
The Fluid Target: 400–800ml Per Hour.
This varies wildly. If it’s a crisp morning in London, you’ll need less. If you’re running in humidity, you’ll need more. A simple way to check your needs is a "sweat test": weigh yourself before and after an hour-long run. Every 1kg lost is roughly 1 litre of fluid you didn't replace.
The Sodium Target: 300–800mg Per Hour.
Sodium is the "glue" that helps your body actually absorb the water you drink. Without it, the water just sits in your stomach (the dreaded "slosh") or passes straight through you. If you finish a run with white salt crust on your face or kit, you’re a "salty sweater" and should aim for the higher end of that scale.
Training the Gut
You wouldn’t turn up to a marathon without having run more than 5 miles, so why would you turn up without having tested your fuel? The gut is a muscle that can be trained.
During your marathon training plan, use your weekly long runs to practice. Start with 30g an hour and slowly increase it. If you feel "niggles" in your stomach, back off slightly, then try again the following week. We want your digestive system to be as bored by your race-day fuel as you are by your morning porridge.
The Trap: Waiting Until You Feel "Off"
The biggest mistake I see is the "I feel fine" syndrome. You feel great at mile 6, so you skip a gel. You feel strong at mile 10, so you skip the water station.
Fuelling is proactive, not reactive.
By the time you feel light-headed or your legs start shuffling, the energy deficit is already too deep. You are essentially "absorbing load" that your body can't sustain. I tell my athletes: stick to the plan, even when you think you don’t need it. Discipline in the first half of the race earns you the right to compete in the second half.
How I Support My Athletes
Personalised coaching isn't just about giving you a list of intervals. It’s about looking at the "system management" of your entire life and race goal. When I build a personalised plan, we don't just talk about pace; we talk about what you can actually digest.
We look at:
- Your history: What has worked (and failed) for you before?
- Your environment: Are you training for a hot race or a cold one?
- Your schedule: How do we fit "gut training" into your busy life?
I provide ongoing feedback. If a certain brand of gel makes you feel sick, we adjust. We adjust the load. We find the "why" behind the performance.
Key Takeaways
- Carbs: Target 30–60g per hour. Start early.
- Fluid: Aim for 400–800ml per hour based on sweat rate.
- Salt: Include 300–800mg of sodium to aid absorption.
- Consistency: Practice every single long run. No new fuel on race day.
- Proactive: Eat and drink before you feel you need to.
Frequently Asked Questions
Can I just use "real food" like bananas or dates?
Yes, but be careful. Real food takes longer to break down and can lead to GI distress when you’re running at marathon intensity. Gels are designed to be "pre-digested" for quick absorption. If you use real food, save it for the early miles when your heart rate is lower.
What if I can't stomach gels?
Look into "liquid fuel" (high-carb drinks) or energy chews. Some athletes prefer the texture of solids over the viscosity of gels. The goal is the carbohydrate count, not the delivery method.
Should I carb-load the night before?
Carb-loading happens 36–48 hours before the race, not just the night before. Shovelling a massive bowl of pasta at 8 PM on Saturday often leads to a heavy stomach on Sunday morning. Focus on high-carb, low-fibre meals for two days leading up to the start.
Need a plan that goes beyond the miles?
I specialise in bespoke online coaching for everything from 5Ks to 200-mile ultras. If you're tired of generic apps and want a human approach to your training, let’s chat. I’ll help you manage the load, nail the nutrition, and cross that finish line strong.
Coach Steve with athletes Leanne, Angharad, and Sian at the Newport Marathon.
