Red,

Couple of thoughts from my experience with running and exercise.

After 3 years I still need to monitor my heart rate during exercise...if I get up on the higher
Aerobics end for extended periods I get payed back. If I push I can for around 5 min then have to let it come down to moderate levels, it's still a good workout.

I can't run since my accident on the street so I run on an inclined treadmill. The incline seems to take the jarring out. I wish I was outside but I'd rather do something than nothing.

Bud