Fueling the Grueling Marathon Miles

You see plenty of weary runners guzzling sports drinks, like Lucazade Sport, on events such as the London Marathon without really knowing what it’s doing to their body and how much they should be knocking back at each mile.

But to understand why and when you should consume sports drinks & gels, it’s first helpful to know a bit about the way your body uses fuel for exercise, and why you get tired on a long run.

Muscle Power

When you start exercising, your main supply of fuel is the glycogen that's stored in your muscles and liver. But this is in limited supply. The harder you work, the faster it’ll run out.

As you tick off the miles during a marathon, your body starts to burn proportionally less glycogen and instead turns to blood sugar and body fat for energy.

Fuel for Thought

However, your brain relies on blood sugar to function properly, and it simply can’t let this supply run out. So as levels drop, your body increasingly switches over to fat as a preferred fuel source.

Unfortunately fat, in comparison to blood sugar and glycogen, takes much longer to be converted into energy. The more your body relies on fat as an energy source, the slower and harder things become.

On top of that, converting fat into fuel requires considerably more oxygen, so you’ll also become increasingly out of breath too!

From relative comfort into pure torture!

After about 2-3 hours, you may develop temporary hypoglycemia. At this point, your body has a depletion of muscle and liver glycogen stores together with low blood sugar levels.

Runners call it “hitting the wall” whilst cyclists refer to it as “bonking”. Symptoms include light-headedness, heavy legs, severe tiredness, and you generally feel like you’re giving a 16 stone man a piggyback!

Read "What’s the Point of Sports Drinks & Gels?: Part 2" to find out how you can make things easier!