Marathon: how to fuel up for the distance

A marathon is a test of body and will. Whether you’re doing a ski marathon in the Otepää hills or running a long trail, your body’s energy stores run out much sooner than most people expect. When that happens, neither willpower nor training will help. In this article, we look at what you actually need to finish a long distance strong.

Why a marathon demands fuel on the course

Glycogen stores in the muscles and liver typically last about 60–90 minutes under training load. In a ski marathon, where the distance is 30–53 km, those stores run out when you’re only halfway there. Without extra energy, you hit what competitive athletes call “the wall” — your muscles refuse to work, your pace collapses and your head starts to swim.

Winter weather makes things harder. Frost means more than just feeling cold — your body burns extra energy to stay warm. In a winter marathon, energy needs can be 10–15% higher than in a summer run or in indoor training. That’s not an exaggeration; it’s physiology.

The practical takeaway: replenishing your energy has to begin before you feel a drop — not after it. If you wait for hunger or fatigue, you’re already too late.

Carbohydrates and gels: a marathon needs fast energy

On the course, energy has to get into your body quickly, which makes short-chain carbohydrates an endurance athlete’s best ally. The general sports nutrition recommendation is 30–60 g of carbohydrates every 30–45 minutes — this keeps your glycogen stores steady and stops your blood sugar from dropping suddenly.

Gels are absorbed faster than bars, but using them together gives the best result: a gel delivers a quick burst of energy, while a bar provides longer-lasting satiety and helps you avoid the one-note sweetness that becomes tiresome on a long course.

All three fit in a back pocket and weigh very little together — a big advantage when you’re counting every gram on the course.

Magnesium and cramps on a long distance

Magnesium gets too little attention in training — until the first cramp hits. Sweating removes magnesium from the body faster than is usually assumed. Losing even 3% of your body weight in fluid noticeably affects muscle function and increases the risk of cramps. Over a long, intense distance, especially in the cold, a deficit builds gradually and unexpectedly.

A liquid magnesium solution is absorbed faster than tablets — an important choice when time is critical. To prevent muscle cramps, specialists recommend taking magnesium before taking on a heavy training load rather than waiting for the first symptoms.

A practical tip: take your magnesium 20–30 minutes before the start. If you feel your legs starting to cramp on the course, your body has already built up a deficit — by that point, it’s better to have the magnesium already in your system.

FAQ: common questions about marathon preparation

When should I take my first energy gel?

30–45 minutes after the start — even if you don’t feel any lack of energy yet. A glycogen deficit builds up quietly and becomes noticeable only when it’s already too late. Prevention is easier than recovery in the middle of the course.

Do bars and gels go together?

Yes, and that’s exactly why combined solutions make so much sense. A gel gives you a quick punch, while a bar adds longer-lasting satiety. A mildly sweet bar is also easier to stomach once a long distance starts to make a sweet gel tiresome.

Should I try sports nutrition before heading out on the course?

Absolutely. Your digestive system often tolerates things differently under training load than at rest. A gel that feels neutral at home can upset your stomach during intense effort. Test every product at least once during a longer training session — don’t use it for the first time at the actual race.

Author: Turg.Fitness.ee

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