Usually late 40s, sometimes early 50s if feeling ropey.
Frightening thing is I've had to have several medical tests because, according to my Garmin, and the Polar, I bought to double check, it can go up to 240 on a long,hot run!!!! Not doing hill or intervals,(180 max) - just when I'm doing a very long run. My doctors were adamant that I'm not going to drop, and the medical advice was not to wear my monitor as they think it's partly down to anxiety.
Incidently, my mum was a champion, record-holding cyclist, in the 1950s, who's heart rate was so low, she had doctors waiting to test her coming off the tracks and velodromes.
Oh, and I'm 55.
Edited: 09/09/2012 at 15:22