I've never been able to run any distance.
Going back to my younger days I played football twice a week, trained once, played American football every week and trained once. I also played squash. In fact, my only day where I wasn't playing sport or training for it was a Friday. At the time I was as fit as a butchers dog and really slim, unlike the heavier person I am now in my late forties. Back then I could run around a football pitch for 90 minutes and not break a sweat but if I was asked to actually just do a lap of the pitch......I couldn't.
I've put it down to that when playing a sport you are pre-occupied with where you should be, what the opponent is doing etc. etc. Essentially, you're distracted from the mental aspect of the exercise. When running though you have nothing to occupy your mind except running. I firmly believe it is a mental block.
I cycle regularly and am doing a 300 miler in August from Germany to the UK (pre warning of sponsorship request

) for charity. I would like to be able to run as some of those mud events look like they would be fun.
Mrs Spudmasher can run like a whippet!