Sunday, November 23, 2008
Running Shoe Cushioning: Perception and Reality
The running shoe industry has built much of its platform on cushioning. In studies by Benno Nigg ,very soft shoes will bottom out when loaded, producing higher impact forces than firmer shoes that do not bottom out. Yet for any of us who have run downhill on concrete the more cushioned shoes seem to be less jarring so how do we reconcile this? I interviewed Benno Nigg, one of the foremost biomechanics gurus on running shoes and he was able to provide a new paradigm which he has published on. He started by telling me that there is no article in the literature which supports the notion that peak force transmission will be altered with varied levels of cushioning. In fact peak force transmission does not occur during heel contact as we might intuit but in midstance where the internal forces in joints muscles and tendons are 4 to 5 times greater than during impact There is something else that accounts for the perception that we are more comfortable in a certain level of cushioning. That something else is explained in Benno' Nigg's vibration model. When we impact the ground our soft tissue compartments (e.g. calf, hamstrings etc.) start to vibrate. However the human body does not like vibrations. Consequently, muscles are activated to dampen these vibrations. The degree of dampening that occurs in various types of shoes is what leads to our perception of comfort in the shoe. Cushioning is better represented by examining the vibrations that travel up the lower extremity according to Dr. Nigg. So we have an innate sense of what works for our bodies that is probably more accurate than any test could demonstrate for us. We must also consider the fatigue that occurs within the muscles that are working to distribute the vibrations. We know from other studies that fatigue can lead to injuries and this may be part of the answer we seek.