I work in carbon fiber. It's light, strong, and maintains a stiffness based on thickness that if tweaked juuuust right, provides a spring of energy return at the moment the proximal tibia advances over the toes. It's not toe-off i'm concerned with, it's the assistance of the body's COG to get forward. By the time the heel is off the gound is too late. But if I can help the heel to rise from the return of energy stored by pronation in the mid-foot, my mission has been accomplished.
Chris Gracey MPT, Cped