The two weeks that decide whether your training shows up on the clock.
Hi, I'm Grace. I'm a Senior New Product Development Technologist at Science in Sport, and I'm chasing a marathon PB of my own.
You've trained hard for months. Every hour and every mile's been focused on arriving on the start line in the best possible shape.
And then, far too often, the final weeks trip runners up.
For some reason, tapering and carb loading are made to sound far more complex than they really are. In reality, they're well-established strategies designed to optimise performance — by reducing accumulated fatigue while maximising carb availability before race day. And they're not just for elite athletes. They benefit marathon runners at every level.
Understanding the mechanism helps us here. Your training produces two things at once: fitness, and fatigue.
Reducing your training load — and paying real attention to your nutrition — lets you deal with the fatigue. Repairing muscle. Refilling your energy stores. Refreshing your mind.
Over a short period you generally don't lose the aerobic fitness you've built. What you do lose is the tiredness sitting on top of it. And that's the whole point.
So let's be clear. Done properly, tapering and carb loading aren't undoing the benefits of your training. They're unlocking them.
Tapering isn't about stopping completely. It's pulling back just enough to let your body absorb the work you've already done.
The standard window is two to three weeks, usually starting after your full race-rehearsal session. From there in, you're gradually cutting your mileage down.
The most common mistake in the final couple of weeks — and it's completely understandable — is panicking that you're losing the gains you've made. Or feeling guilty for resting more. So you up your mileage.
Don't. Resisting that natural urge is a large part of smart tapering.
You're not going to get any fitter at this point. But you can get fresher. And freshness, alongside good fuelling, is what brings the fitness you've already built to your race performance.
So what about carb loading?
Through the taper period, don't change a thing. Regular, balanced meals, and solid hydration.
Then, 48 hours out, carbs become your top priority. We know we store carbs as glycogen, and race pace burns through it fast. So you want to start with those stores as full as possible. That's all loading is. Filling them, calmly, smoothly, and steadily.
Where many runners still go wrong is the old idea of a huge plate of pasta the night before, or something heavy an hour before the gun. There's no need for either.
Instead, just gently increase the proportion of carbs in all your meals across those two days. Keep it familiar — light, plain, carb-rich foods, and keep the fibre low.
And be accurate with your carbs. Don't guess. Work out a target number, based on your weight — aim for 10 to 12 grams per kilo, on both days. Spread that total evenly across the whole day, shared between all your meals and snacks. Don't forget drinks and supplements count too.
Then on race day, depending on your start time, top up three hours out and again one hour out. (Covered fully in the next episode.)
Good carb loading is all about being calm, controlled, and predictable — just like we want your run to be.
Your two to three weeks of tapering and your two days of loading go hand in hand. Together they're the bridge between your months of training and your big day.
Tapering and carb loading are more straightforward than most runners think. The good news is a relaxed, patient, no-panic approach is all you need.
Trust the science. Trust the process. Trust your training.
So build strict plans now for your tapering and your carb loading. Then when the time comes, stick to them, even when you're tempted to improvise.