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.