How much is too much?

I read an article today that I wanted to share with you all about how much exercise to get and how much is too much.  It is good, quality information for all to read.  Here is a short quote from Dr. Kenneth Cooper to give you some food for thought and a small glimpse into this article:
If you’re running more than 15-20 miles a week, you’re doing it for reasons other than to achieve good health.


What is your reason for exercise?  Is it to achieve good health, or is it something else?  There are plenty of other reasons that may very well be ok, but it's good to recognize what reasons are behind how much you do or don't exercise.