I run between 3-5 times a week, the runs range from 3.5 miles to 7.5 miles and I tend to run mid/late afternoon or early evening. What I have begun to notice is that some days I can have a really good 7.5 mile run - I really enjoy the run, have a good pace, and my lungs don't feel like paper bags. However, on somedays it can be a struggle to do a 4 miler, I breathe a lot heavier and start taking deeper breaths earlier into my runs than usual, and it is a real effort to make the distance. Yet a day later or before, I could do a really good 7.5 miler. Firstly, I suspected some pace differences. After a week of conciously keeping my pace in tempo - I found my running experiences to be much the same. Some great, some shite. Now I'm wondering whether it's about my energy levels and the food I eat. Given that I run during the times I do, I've eaten throughout the day (had breakfast, elevenses, lunch and usually a mid afternoon pick me up) I've always tried to have a good and varied diet, I don't smoke, I don't even drink. But I don't have a set out eating plan. My question is this: Should I be running when I have had very little to eat, or when I have fed substantially? The problem, I suppose, is that I'm finding it tough to gauge my fitness and any improvements I'm making when my running experiences are so erratic. Should I be gauging my fitness levels on how far I can run with or without "feeding up"? Any help or advice would be most helpful. Cheers for your time. Hed.