Hi, I'm Grace. I'm a Senior New Product Development Technologist at Science in Sport, and I run.

Whether this is your first marathon or your tenth, it's a big day.

The occasion, the crowds, and the nerves all make a difference — and that's exactly when you need a rock-solid race routine you can trust.

Because the runners who finish strongly don't get there on luck. They build a plan in training. They practise it. And they stick to it on race day. It's time to build yours.

The marathon is predominantly aerobic. Your body uses both carbs and fat for energy. But as the race goes on, carbs become increasingly important.

Running 42.2k at marathon intensity places a substantial demand on your carb stores. Over the course of a race you can use several hundred grams, depending on your pace, your body size, and your time on the course.

As the race progresses, carb availability can become limiting. When that happens, maintaining your target pace becomes increasingly difficult. That's the experience most runners know as hitting the wall. It's still surprisingly common in every marathon — and it's also largely avoidable.

So pre-race loading and in-race fuelling are both essential. Let's break your race-day nutrition down by intervals, to put together a plan you can rely on.

Ideally, you've been carb loading steadily for two days. (Covered in the episode on tapering and loading.)

That brings us to the big day. Race-day fuelling isn't complicated. It just has to be decided long before race morning — because that's the worst possible time to be making decisions.

Overnight your liver glycogen naturally drops, so the first job on race morning is restoring it. This is done with carbs.

Have your main pre-race meal — usually breakfast — around three hours before your start time. Aim for roughly 3 grams for every kilo of bodyweight, from your usual light, familiar, easy-to-digest foods.

Hydrate steadily, adding electrolytes based on the conditions.

Then an hour out, a small top-up. 20 to 30 grams of carbs, from food or a gel or drink. Keep fluids going gently, easing off as you get closer to race time.

That should get you to the start line with enough stored glycogen and good hydration.

Right. It's race time. You'll have worked out your fuelling numbers in training, based on your realistic finish time — not at the start line.

A practical target for many marathon runners is around 80 grams of carbs every hour — with up to 120 grams an hour suitable for experienced, competitive runners who have specifically trained their gut to tolerate higher intakes.

Always go with the volume you've established you can tolerate on the move. Not the one on the packet, and not the one your training partner uses.

Intakes at that level are exactly what dual-source products were developed for. Combining maltodextrin and fructose allows higher carb intakes to be absorbed and used, while minimising gut discomfort. That's why BETA Fuel, including BETA Fuel 80, is a tried-and-tested marathon choice.

Timing's important. Set your fuelling intervals and keep to them. Because consistent, predictable intake means smooth energy availability.

And stay ahead of any potential slump. By the time you feel your tank's getting low, you're already behind it.

You'll have established in training what products and flavours work for you. Stick to them, and nothing else. Race day is not the time to try anything new.

Hydration works the same way. Match it to the conditions rather than to a fixed volume. Use the aid stations, and take regular, steady, small amounts rather than too much in one go. Over-drinking is as unhelpful as dehydration.

Electrolytes matter too, particularly sodium. How much you need depends on how much you sweat, the concentration of your sweat, and the duration and conditions of the race. Something like HYDRO tablets makes that easy to manage.

When things get challenging out there, lean on the good habits you've developed in training. You're just repeating what you already know works for you.

That's how you stay focused and in control. That's how you deliver in the final 10k, when you start thinking about what time you could achieve. By sticking to your plan.

A marathon throws enough at you that you can't control. So make the most of the things you can. Your race-day nutrition is one of them — probably the most important one.

Quality, volume and timing. Trust the strategy you built in training. When you get it right, everything feels better — your pacing, your rhythm, your confidence. And that PB you're chasing becomes a reality.

So well before race week, write your three carb numbers down. Your breakfast target, your one-hour-out top-up, and your mid-race hourly rate.

Then go fuel the marathon you're capable of.