Marathon training: taking liberties with fuelling … bad idea

Yesterday’s long slow run was very hard. It was the longest I’ve done in this training programme so that’s not too surprising – but it felt harder than could be explained by just the extra two miles.

I was wondering if it was simply a bad run or whether nutrition was at the root of it. I never understand it very well, but I had a look at the science …

The internet says (so it must be true!) that someone my size burns somewhere between 100-115 calories per mile on a steady paced run. Taking the larger figure (as I doubt that I am an efficient runner) that suggests I might have burned around 2000 calories over the 17.6 miles.

I ran on an empty stomach and without taking water with me (as usual, I know, very foolish). I had one cheap cereal bar on the way round (a mighty 87 calories, so it claims) so that left me with 1910 calories to find to fuel the run.

Again, the internet suggests I can probably store about 1400-2000 calories of energy in glycogen. As I’d had nothing other than a cup of coffee (no sugar) before the run, I doubt that I was completely topped up with glycogen stores since eating on Saturday night (indeed, I’ve read that the glycogen can be 50% depleted overnight). All that suggests that I ran out of readily available energy during the run and had to start burning fat – and that’s not very efficient. I guess I got pretty dehydrated too (even though it was fairly cold) – a bad combination but I wonder which was the biggest factor?

I didn’t hit any sort of wall, but Jackson Browne’s ‘Running on empty’ comes to mind.

According to the scales this morning, I lost 0.6kg (1.3lbs) yesterday, despite eating and rehydrating after the run. That feels a bit high – but if I had a deficit from the run, and had to fuel my body for the whole day quite apart from the run, it makes at least some sense.

In addition to the run being fairly slow and laboured, I also had more quad aches after it than usual and my knees were sore for the first time. I wonder if that’s anything to do with nutrition or hydration?

Interestingly, the figures suggest that I’d burn between 2600 and 3000 calories for the marathon – that’s less than I might have guessed and indicates that if I start with a full tank of glycogen, the number of extra calories needed to fuel the run is relatively modest.

Anyway, the aches and pains have almost gone and even the Achilles’ are behaving themselves fairly well. The shoulder I hurt skiing is still improving and the weather is getting better.

Could be a lot worse, as long as I learn my nutrition and hydration lessons for the long runs.

6 thoughts on “Marathon training: taking liberties with fuelling … bad idea

  1. Julie

    You definitely made it hard for yourself! Did you ever use the gels? I use them for the long runs and find them good – I know they don’t suit everyone. I take one every 5 miles or so, about 100 calories and 26g carbs I think. For all the things I did wrong in the marathon, my fueling was good and I didn’t hit the wall. Well done on the distance!

    Liked by 1 person

    1. The Omil Post author

      Thank you. I’ve used gels while on the bike but, oddly, not for running. I was slightly put off them when I squirted myself in the face with one riding the Etape du Tour in 2013 – and spent many miles in an unpleasant sticky mess. I think you’re right, I should look for some gels and some of the isotonic energy gels (I guess they are just diluted versions of the normal gels) as they might mean I don’t need to carry water.

      Liked by 1 person

  2. Paul Twedt

    I’ve done the same before, running a long run (20 miles) with no fuel or water, but my intent was to hit the wall and bonk so I would know what to look for in terms of warning signs and feelings as I approach that point. It was MISERY! One of my roughest training sessions ever. But also, now I know I can still survive it, and that makes me a stronger runner. When considering using gels, I would be sure you still have some water available, at aid stations within a few or five miles, as the gels can turn your stomach if not diluted with some water. I’ll have to check into those isotonic gels. Cheers mate and happy trails!

    Liked by 1 person


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s