tytbody, I've been running since the early 1980's but I only started using a heart-rate monitor about 3 years ago.
I started when I was in the Army where they require a 2-mile run test, and have increased mileage over the years, although I walk more now than I run. I did the Four Day Marches Nijmegen (or Vierdaagse) in 1999 which was the hardest overall distance I've done (25 miles per day for 4 days). I always wanted to do just 1 ultra-marathon, but now that I'm in my 50s I may have to stick to lesser mileage. On the other hand, when I ran in the Marine Corps Marathon 4 years ago there were some 80+ yr-olds who finished (and a couple of 60+ yr-olds ahead of me

) so age is not an excuse I guess.