For one reason or another — as a scientific advisor, peer-reviewer, or just to stay current — I read a lot of scientific articles. And every so often, I might say out loud, “Now THAT was a really nice study.” Myself having published many scientific studies, I’m adept in appreciating those that are especially meaningful.
Let me begin by saying that there’s been this long-held belief that the muscles in the arch of our foot are inconsequential to supporting the arch when we stand, walk, and run. Going along with this belief, for the last hundred years, virtually all shoes – from dress and comfort shoes to athletic shoes – have been constructed with a built-in arch support. In fact most shoe companies and shoe stores thrive on marketing this arch support. Just go to a typical shoe-selling website and see how shoes are often rated on the basis of how much arch support they provide.
Well, last month, Glen Lichtwark and his research team at the University of Queensland published a study of the muscles in the arch of our feet using a technique known as fine-wire dynamic electromyography. Before I give away the results of their study, let me explain the technique they used.
Fine-wire dynamic electromyography, in conjunction with kinematic and kinetic measurements, although time-intensive, provides the most comprehensive method for determining the functions of any particular muscle in the body. In fact, knowing how useful fine-wire electrode studies are for determining muscle function, I once published a method for preparing fine-wire electrodes. Like many physicians specializing in this type of study, I’ve measured electrical activity of muscles and electrically stimulated muscles in thousands of patients and research subjects so as to diagnose problems as well as to define normal muscle functions.
Basically, a pair of thin, flexible, fine-wire electrodes (an active and a reference electrode), is used to both record muscle electrical activity as well as stimulate a muscle while the subject performs a specific task. In a sterile setting, the wire electrodes are pre-threaded into a hollow needle, the needle is inserted into the muscle, and then the needle is pulled out, leaving just the two fine wires in the muscle. Simultaneous with the muscle being recorded or stimulated, motion and forces are measured typically in a sophisticated motion laboratory with a 3-D motion analysis system in conjunction with force plates. When the study is complete, the wires are pulled out.
Using this technique, Lichtwark and his team studied the three largest muscles that are intrinsic to the foot: the abductor hallicus, the flexor digitorum brevis and the quadratus planae. “Intrinsic” refers to muscles that start and end in the foot.
They placed electrodes into each of these muscles and first had the subjects sitting with their feet gently touching the ground. They then placed an increasing amount of weight at the end of one thigh so as to simulate the forces that occur when we stand, walk, and run. As the weights were increased, the arch of the foot gradually flattened out toward the ground. Along with this gradual flattening they observed increasing amounts of muscle activity from each of the three muscles. Next, with weights still applied to the end of the thigh, they electrically stimulated the muscles. The stimulation of each muscle significantly raised the arch of the foot from the ground.
What this says is that without any interference from, say, cushioning under our foot arch, our arch muscles play a substantial role in supporting our arches when we put weight through them, as in when we stand, walk, or run. The type of active resistive response they provide is consistent with most every other muscle in the lower extremity. For example, during walking and running, our quadriceps muscles actively resist our knee collapsing into flexion.
The results indubitably dispel the belief that the muscles in the arch of our feet are inconsequential. Even when the arch of the foot completely collapses under the weight of the body, (such as occurs in people with “flat feet”), there is increasing and substantial active resistive muscle activity that is simultaneously occurring. Given what we know about the importance of small muscles in controlling proper postural alignment throughout the body; for example, the role the small rotator cuff muscles play at the shoulder, it’s unfathomable to think that these foot arch muscles aren’t important in properly aligning our posture. Or to believe that a cushioned arch support could ever, in a million years, substitute for the complex combination of forces that these small muscles apply.
One more thing that Lichtwark and his team did in this study is measure the center of pressure under the foot. The center of pressure is basically the point under the foot where our bodyweight is centralized. They found that electrically stimulating the abductor hallicus while weight was applied to the end of the thigh, caused the position of the center of pressure under the foot to shift laterally, to the outside part of the foot.
Given the work I’ve done in measuring forces across joints during walking and running, I’m especially appreciative of the meaning of this latter finding. The center of pressure is a significant determinant of the forces occurring through the joints. Such that even a slight shift in the center of pressure will significantly affect the forces through all the joints, but most importantly in areas where we are prone to osteoarthritis.
I’ve shown that virtually every type of non-OESH, traditional shoe (from dress to athletic) shifts the center of pressure medially compared to barefoot, thereby increasing forces through the joints, including through the inside part of the knee where we are prone to osteoarthritis. (Not a small matter especially for us women who get it nearly twice as often as men and in whom it causes more physical disability than any other singular disease). There are many facets of a shoe that work in combination to substantially affect this shift in center of pressure and subsequent joint torques and forces, with a cushioned arch support being one of them, as we showed here.
Lichtwark’s study might help explain some of the mechanism behind our center of pressure and joint force findings. If the abductor hallicus is inhibited by a shoe’s arch support, then the abductor hallicus can’t actively help shift that center of pressure, ever so slightly, laterally, which would help minimize the forces through the joints.
Old beliefs die hard especially when they’re supported by a multi-billion dollar shoe industry that thrives on manufacturing and marketing built-in arch supports. Some time ago I gave up trying to convince the industry with research. It’s been far more rewarding to just build my own factory, make shoes that have, among other things, absolutely no built-in arch support, and share in the joy that occurs when an OESHer learns for herself what her little arch muscles actually CAN…and DO, when given a chance.