Posted: 26/01/2016 at 10:49
I'm going to disagree with my far more accomplished friends Jimbob and RR. I don't think the slower pace of the long run is to help you learn to burn fat. Why do I say that? Because on both hose training runs and during the marathon we take in almost pure carbs as fuel - and as long as we do that, there is virtually no fat burning going on. None. To burn fat as fuel, you have to be glucose depleted. So, if you want to train your body to use fat as fuel - which you can do - you need to train and race without using carbs.
The purpose of going slower on long run training is to enable you to still have quality training sessions in the days following the long run, and not be too trashed to do that.
Hmm .... agreed you won't burn any fat on a short slow run, but on a longer workout you burn fat and carbs at the same time, if it's slower you burn less carbs giving you more reserves. The purpose of the session is to not to train yourself to use fat as fuel but to make your carbs last you longer. But of course, if you run it too hard you will knacker your training for the following few days having a negative effect on your other training sessions..