Ask the Coach: I keep fading badly after mile 18 – is this a pacing issue or a fitness issue?

Hi Mike, I keep fading badly after mile 18 – is this a pacing issue or a fitness issue?

Mila

Running coach answer: preventing fading after 18 miles

Thank you for the question – the answer can be several things, including pacing, fitness and nutrition.

To tackle fitness first.

One of the objectives of your long runs in training is to develop the ability to metabolise fat as an energy source. To do this, you need to be doing runs of over 2 hours at an easy to steady pace at an early stage in your training block. You also need to do several of them to get adaptation.

Your muscles prefer to use glycogen (carbohydrate) as their primary energy source. The faster you go, the more your body will prioritise glycolysis. The problem is that you have a limited store of glycogen in the muscles – enough for about 18 miles of hard running!

At slower speeds, your muscles will also be able to use fat as an energy source. As we all have a big supply of calories stored as fat, it is something endurance athletes need to encourage.

To encourage your body’s efficiency in burning fat, you should run your long runs more slowly. It is at zone 1 and zone 2 paces – recovery to steady paces – that your body will be encouraged to use fat for energy. As you run faster, the amount of fat used declines and the amount of energy from your limited supply of glycogen increases.

In training, we want to be running mostly at that zone 1 and zone 2 pace.

Once you are an efficient fat burner, your body will be better able to use glycogen and fat together. The proportions it does this will depend on your running speed.

This is where pacing comes into the equation. You need to judge your race pace so that you use glycogen and fat efficiently to give you a supply of energy through to the end of the race.

Getting the pace right is about experience. As a useful guide, you can use heart rate as a measure of effort (pace) – a heart rate of 83% of maximum is about right.

Nutrition is a key area of endurance running. It is good to be well-fuelled with carbohydrate in advance of long training runs, as well as before a long race.

For the marathon, I would suggest eating more carbohydrate foods in the last 72 hours before a race, while also reducing your training to a small volume, so that you have a full tank of fuel before you start.

There are numerous ways of getting carbohydrates into the body during a long run or race, such as gels, blocks, jelly babies, ripe bananas, rice pudding, and energy bars. It is a whole new topic, and what you prefer will be personal to you – not everyone can stomach a lot of gels and taking a gel every 30 minutes in a 5-hour marathon, or a 10-hour ultra, is likely to cause some gastronomic distress.

I wish you lots of luck in your next marathon, Mila.

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