I went for a long, slow easy run of 12 miles today and my average pace was 7:32, which is about a minute slower than my race pace. Thing is I am still knackered after this. I thought the whole point of slow, long runs is that they are meant to be easy. Ok, it was easy on my heart and lungs as my heart rate stayed quite low and I never felt breathless or anything, but the last 2 or 3 miles still hurt my legs. My legs feel as do after a long run at race pace. Is this normal? Should I be running at an even slower pace for my long runs?