One of our friends, journalist Max Lockwood of Running Insight magazine, cut to the chase by asking me a few simple questions this week: What is torque and How bad is it for the runner?
To properly answer Max, I referenced the landmark study we published in 2009, when I was director of the University of Virginia (UVa) Gait Laboratory. We showed that traditional running shoes increase joint torques compared to barefoot. The study received a lot of press and you can find coverage of it online…a site that has the entire pdf available is here.
I included in the introduction and the discussion the meaning of torque, which is, in a nutshell, the body weight force applied a distance from a joint, as well as its potential medical significance. Generally, greater joint torque implies greater loads through the joint and greater stresses and strains through the joints associated muscle, ligaments, and tendons. Peak joint torque is a function of peak body weight force which occurs not at the moment of impact when the heel first touches the ground, but much later when the foot is fully planted.
We can only guess from this study that the raised heel was a factor in raising joint torques because of my previous studies first at Harvard and then at UVa showing that high heeled shoes similarly increase joint torques. The other factors that are likely to play a role are the general foam cushioning and inherent arch support in traditional shoes.
The fallacy in thinking has been that cushioning in shoes somehow reduces pressure on joints. But in fact, foam, gel, “air” cushion and the like simply absorb energy without giving it back, which basically makes the joints have to work even harder. This in turn, places greater demands and thus greater torques, forces, and pressures on the joints. A better sole / ground surface would both give and give back, not at impact when the heel first touches the ground, but much later in the gait cycle when the joint torques are at their greatest. Regarding torque, I always explain the physics by the example of moving a frozen bolt…you can’t do it with a tiny wrench, but increasing the torque via a long handled wrench will move anything…now imagine what that excessive torque might feel like on your joints.