It absolutely does affect my running! In this heat and humidity I'm a good 2minutes per mile slower than what I was when I was training over the winter. It gets me very discouraged, but I have to keep reminding myself it's totally normal in this kind of weather and just think how great winter training will be when it gets here. And just think, if mother nature throws a curve ball and race day for the Princess is warmer than expected (like it was this year!) then you'll be totally prepared! My training for the Dl half is getting close to winding down...we're about a month away now, and it certainly is brutal out there. Luckily, the meat of the Princess training will be in much more favorable weather for you! Hang in there and remember to hydrate