Re:

You're not stupid, so dont' feel that way. Mine is just the opinion of one person - me, and I could be wrong.

I just don't see the body being made for sustained running.

For the evolution people, we haven't evolved into sustained running either, otherwise more of us would be running all the time.

Running on hard surfaces like cement, etc., plays hell on the knees. Where in nature would anyone ever run 20 miles on solid rock ?

cheerio