Sunday, 14 September 2014

Is running LCHF harder for the first 20 minutes?

Here’s An Idea.

“While adapting to burning fat instead of glycogen it may take up to 30 minutes to get into your stride on longer runs”.

This is a thought that has been crossing my mind during the first 2 weeks of reverting to a LCHF diet after 2 weeks on carbs on holiday in France.

The French Experiment is starting to look like a success - by which I mean can I go on a carb-bender for 2 weeks and then easily switch back to LCHF? - after just 8 days back on LCHF I managed a gentle 13 mile run (longer than I have run in 5 months) with none of the classic fatigue symptoms that hit me when I first tried the diet in January.  The intensity is less, and I am mixing the exercise with cycling, but it has been a problem-free return to LCHF so far.

One thing that I have noticed, and I recall this from January; my longer runs and rides have tended to feel harder at the beginning, much harder . In some ways this is not surprising – I'm not an early riser and the knowledge that I am nearing home often lifts my mood and my speed. This week though I have noticed my energy levels rise significantly after 20 minutes or so and then remain that high for the rest of each run/ride.

If true this could explain a lot about why some people reject the diet –“it made me feel worse than ever before when I was running”. But didn't we all feel this way for the first week or so when we first started running? The body has to adapt; only this time it is the energy supply that is adapting rather than the muscles. If false then no matter, it's just an idea.

I have precisely no data to back this idea up; but today's 17 miler was a good example; the first hill was lousy and I had to walk some of it, which is a rear event. Then after 40 minutes I had to slow down a lot as I was daydreaming and casually running much faster than I had planned (my coach/wife thinks this is why I get injured so much!). The second hill at 9 miles was a breeze, as was the third and it was only the fourth at 14 miles that actually had me properly knackered.  

Perhaps it was the gentle breeze behind me!

I don't have a good explanation for this experience; apart from the idea that maybe when we first set off our muscles have some stored glycogen and they want to burn it; but there is not enough so they can't perform; once this runs out the fat-adapted state wakes up and gets to work. 

I can find no articles on the internet that talk about this subject. So, head down and time to find out more. 


  1. Well, I've found nothing at all on the internet on this subject. So I'm going to do some basic experimentation. My last few runs and a long hilly run yesterday (21 miles and 10 hills ) felt just the same with a crappy first hill or two and steady improvement after that. But I did not feel this way when I started out on LCHF in January.

    One possible difference is that I was alcohol free in January. It is quite possible that the better sleep and fewer carbs in January made the difference. One way to find out is to Go Sober for October. So I've signed the pledge and we will see what happens.

    If all other things remain the same and my performance changes having changed this one variable then it could be an interesting find.

    I am also thinking I'll ditch the diet at Christmas and do it again in January. I'm not going to write a paper on it and call it science, but it will be interesting nonetheless.

  2. Too late! The problem went away last week before I gave up on the booze. No difficulties getting up to speed on a couple shorter runs and I did a very hard 20 miles yesterday around Edale with no problem climbing straight up to Hollins Cross from my dad's. I'll just have to put that idea on the shelf for a few months.