Originally Posted by
terrymorse
Agreed, and this brings up the big question:
How can you tell when you are doing too much intense training?
This is just my personal experience but I once had bouts of chest pain in my early 40's, had the range of tests including a stress test and the only thing they told me is that it was possible that overtraining caused it. They were brief but somewhat intense shooting pains experienced at a time when I was doing plenty of HIIT and also lengthy high zone training. This stopped when I backed it off somewhat.
My advice would be to check out articles from exercise/health pros out how much time is typically safe in the various zones based on overall health, age and training status. Listen to your body. It IS possible to overdo it and that can have consequences.