I have just run the hardest 8 miles I have ever done. Don't know if the heat affected me. It was about 21c, which isn't really that hot, but it just sapped my energy. I had done an 8 miler yesterday too, so don;t know if that made a difference too. Or the late night drinking on Sunday may also have played apart. Either way, it was torture. I felt dehydrated 2 miles before the end. I had drunk 2 pints of water before hand. Now my legs just ache like hell. I feel so unfit. I wasn't even going that fast.