A bit about the guy who is trying to compete in the Olympics with artificial legs:

... Robert Gailey, an associate professor of physical therapy at the University of Miami Medical School, who has studied amputee runners.
...
According to Gailey, a prosthetic leg returns only about 80 percent of the energy absorbed in each stride, while a natural leg returns up to 240 percent, providing much more spring.

The lesson here? Never ask a "professor of physical therapy" a question on physics.