Are Soft Surfaces Hard On The Body?
One researcher thinks so.

One researcher thinks so.
Exercise physiologist Hirofumi Tanaka from the University of Texas at Austin bristles when he sees soft-surface running trails.
Why?
Where these appear to be locations for runners to give their body a break from the pounding of the roads, Tanaka, a runner himself, disagrees. When he was recovering from a knee injury, an orthopedist told him to get off the roads and hit the trails. “I twisted my ankle and aggravated my injury while running on the softer and irregular surface,” he recalls.
After this incident, Tanaka took a deeper look at soft-surface running and says he could not find any scientific evidence that a softer surface benefits runners. He also couldn’t find any experts who would take that stance.
Surprisingly, in The New York Times article on the subject, writer Gina Kolata notes that there are “no rigorous gold-standard studies in which large numbers of people were assigned to run on soft or hard surfaces, then followed to compare injury rates.”
The reason: it’s too hard to recruit large numbers of people who are willing to be randomly assigned a running surface.
For More: The New York Times