Quote Originally Posted by HappyAnika View Post
Yesterday was supposed to be a nice easy zone 2 for 40 min. I've been working on increasing my long run time 5 - 10%/week. However my heart rate was really high, I had a hard time keeping it down, I ended up running soooo, sloooooow. About 13.5 min/mi. I felt like I could have been walking faster. My theories on why my hr was so high: a) stress, b) heat (I'm used to running in 55 - 60 degree weather, yesterday afternoon it was 78), c) not yet recovered from mountain half century on Saturday, or d) all of the above. It was discouraging to say the least. I'd started seeing some real progress in my pace for the same heart rate the last few weeks, this felt like a set back. Oh well. I accomplished my time goal, hopefully next time out will be better.

Heat will make a huge difference on the HR. You still need to respect your parameters, you're body is stressing, just for a different reason. It is likely all of the above. You did the right thing to slow down and like KSH said, it'll be getter next time.