Socks - 1 Cal = 4.17KJ.

Ok, i'm going to advise you based on what I have learnt up to and during this weekend. Please don't take any of it as fact, I am still learning and very inexperienced!

With your heart rate, your heart rate training zone or aeorobic conditioning zone should be between 60 and 80% of your maximal heart rate (MHR) or 40-50% if you are a beginner. It's quite difficult to work out your MHR so the best way to do it is to look at a scale of 1-10 (10 being the hardest) if you would rate the activity as a 5 then your PROBABLY working at about 50% of your MHR.

What your body uses to make energy depends on the energy system your body is useing at the time. There are 3 the Anaerobic system (made up of 2 systems) and the aerobic system. Very briefly, the anaerobic system is used for intense, very fast exercises like sprinting or low rep high weight resistance training as it very quickly runs out. It can usually last up about 3 mins. Then your body switches to the aeorobic system which utilises Oxygen (which has no limit) the aeorobic system will burn fat then carbs.

So with distance running you want to improve your aorobic capacity which you can also do by endurance or strength resistance training (you are then using your slow twitch muscle fibres which are the ones activated during endurance activities) so medium weight high reps.

I hope this helps, as I said I don't fully understand it yet so the explainations might not be spot on but the basic principles are right!