The Harvard Indoor Track Revisited (part 3 of 4)
Okay, so the first big difference between cushioning in a shoe and the successful plywood structure of Harvard is that the plywood does not give at impact like a typical cushioned shoe. The second difference, which needs to be emphasized, is that the plywood maximally compresses and releases like a spring when the foot is fully planted. Specifically, the slopes of the rise and fall of the ground reaction force correspond precisely to the equal and opposite slopes of the compression and release of the plywood surface.
While the athletic shoe industry has been designing around trying to cushion impact, any data we may have seen regarding midsole compression relates to what occurs at impact, not what occurs when the body weight force and all the stresses and strains in the body reach their peak. Foam, gel, and air bladders are incapable of providing the same spring like compression and release that Dr. McMahon showed with his plywood structure. Sure, the typical ethlyne vinyl acetate (EVA) sole of the shoe may give underfoot but it doesn’t give back like the plywood spring.
Over these last 30-plus years, nothing has really changed in the design of the typical athletic shoe. It has been mostly about cushioning impact combined with varying amounts of trying to control foot pronation.
So, with all we now know about how the Harvard Indoor Track works, and how the current athletic shoe doesn’t work, how to we go about making a better shoe?
From a biomechanical standpoint we know that attempting to cushion impact reduces feedback to the body, resulting in altered muscle activity and foot position at contact. It has been shown that making impact with a soft surface can actually increase injury. And most recently we showed that a typical cushioned running shoe increases peak knee joint torques associated with knee osteoarthritis.
With all of this in mind, I am hearing that ‘crack’ of the pistol, and tomorrow I’ll take you on our gun lap around Harvard’s Track.