The point is that world-class runners from countries in which most people train barefoot have far fewer foot defects than people from rich countries who are engaged in the exact same occupation.

What does {{fact}} mean?

How do you know this? Is there any real data on this topic?

I know about and keep up with this topic because of my background. It's not the result of a casual google surf.

Hartman's work with over 100 world class athletes is "real data". Aside from that, there's a great deal of literature about overpronation, probably the most common bio-mechanical foot defect in runners from rich countries. Additionally, has been conducting research about this topic for a while. In fact, the American Academy of Physical Medicine and Rehabilitation published a couple of months ago, saying that running shoes often increases joint torques at the hip, knee and ankle. Their study did include athletes and did look at long term bio-mechanical defects in those who wore sneakers of varying degrees of padding.

You may not be able to find all of this data for free from your computer desk, but it does exist.