[pg314]

You didn't define 'extensive'.

Is it 20-30 miles/week over a long period, which you claim is already way too much for the majority? If I read study [1] correctly the runners were running 3.5 hours a week at the beginning of the study, which would be around 20 miles/week. That same group had a lower incidence of osteoarthritis than the control group.

Do you have any evidence to back up your claim?