August 2021

Insoles to Mazimize Proprioception, Part I

By Mark Cucuzella, MD, FAAFP

The whole concept of minimal shoes is to give the runner an experience similar to what they would get if they were actually barefoot. A primary goal is to get the athletes in the least amount of shoe that is safe for them today and gradually reduce the shoe as the foot strengthens.

One of the main benefits about being truly barefoot is maximizing proprioception, the valuable sensorimotor information we receive from the foot/ground interface. The foot’s dense proprioceptive system plays a critical role in the activation and efficiency of muscles controlling gait, posture, and alignment.  When we introduce a layer between the sole of the foot and the ground, we add a layer of sensory insulation. So, let’s look at the role of a critically important aspect of the shoe – the insole layer, the layer that is in contact with the foot.

Insoles have traditionally been broken down into 3 main categories; cushioning, support, and custom orthotics. Recently a 4th category, foot strengthening or proprioceptive feedback insoles, has been introduced.

The cushioning products use terms like shock absorption and energy dissipation. The basic premise is that the material, through physical changes in the material properties and /or material breakdown, dissipate harmful impact energy and provide cushioning. Top products in this category, SofSole and Spenco, use materials with viscous properties. The viscous property materials tend to be heavy, and the softness of the product dampens our interactions with the ground.  This does not produce the desired effect for efficient walking and running activities.

The second category of insoles support the foot, and most commonly the foot’s medial arch. Variations of these insoles exist which feature wedging effects to alter pronation. These insoles mimic the custom orthotic concept. Variations of these insoles also exist where you can heat form the insole to match your foot, making it more like a custom orthotic products.  In the support category are Sole, A-Line, and Superfeet. In many cases, the brands offer devices that both support and cushion.

Another device is the prescription orthotic. Websters’ Dictionary defines an orthotic as “a device (as a brace or splint) for supporting, immobilizing or treating muscles, joints or skeletal parts which are weak, ineffective, deformed or injured.” Although typically not sold at retail, virtually every retailer has a percentage of consumers who come in and must ensure that their orthotic will fit into their new shoes. Although I believe there are several structural flaws in the human frame that benefit from orthotics, we often take a structurally normal foot, which has atrophied through years of bracing and support, make a cast of the weakened foot, and make a support to brace the weak foot. We allow the foot to continue to weaken and make another pair in a year.

Taking the foot and making it reliant on a brace or support is counterintuitive to those wanting to strengthen and rehabilitate so the foot can become a self-supporting structure.

Once a joint is braced, it will often require bracing indefinitely until an active rehab is prescribed.

Athletes embracing the healthy foot movement desire the following:

1) We don’t want sensory insulation

2) We want full foot range of motion

3) We do not want excessive bracing, cushioning or support.

A unique category of insoles is a proprioceptive-based insole by Barefoot Science. This is not a new concept – Barefoot Science insoles have been around for almost a decade and the underlying science it is based upon is 2 decades old – but today it is getting looked at anew.  The patented insole focuses on the use of the body’s own sensory perception and proprioception to introduce a mild stimulus to a region corresponding with the foot’s center of mass. The body’s natural response to the stimulus is to move away and thus a series of continuous and minute muscle contractions are begun. The insole works with a progressive series of inserts, much like a progressive resistance training program, to gradually introduce this muscle strengthening component to the foot. So, as opposed to the concept of brace or support or the concept of cushion and insulate, here the concept is strengthen / rehabilitate. For those of us that have begun questioning the benefits of the brace-support and cushion footwear products, this makes perfect sense.

Another interesting aspect of the insole is how it interfaces with the foot. The science of typical insoles focuses on primarily supporting the foot’s medial arch and possibly, depending on product, the transverse and lateral arches. The shape and concept behind the Barefoot Science device is in the interface with the foot’s centre of mass. This key region aligns with the body’s line of action through the foot and thus it creates a dome-like effect that the foot can rotate about. From an anatomical point of the view, the hip is like a ball-socket, the knee is like a simple hinge, and therefore the foot, to interact multi-directionally with the ground, needs to have a ball-socket multi-directional capacity as well. This aspect is especially beneficial for those running or doing any sports on uneven surfaces.

Apart from the sock, the insole is the layer in most immediate contact with the foot. The features and benefits of this insole come as close as can be found to bringing the benefits of actual foot/ground interface inside the shoe to the foot/insole interface. It is also transferable into daily footwear, effectively providing progressive barefoot like stimulation for every step taken, which should, in theory, reduce the injury rate and shorten the transition time that some have associated with the minimalist/barefoot transition.

Overall, the advantages of improved foot strength translate into more efficient and a less injury prone movement. The natural mechanics of the musculoskeletal system are capable of providing the shock absorption and support our body requires for most activity.

Insoles focusing on the strengthening and rehabilitation of the foot make sense for not only minimalist runners but for the entire shoe-wearing population.

Part 2 will focus on the science behind strengthening the feet and why the center of mass is critical in this paradigm.

Lt. Col. (Dr.) Mark Cucuzzella is a Professor at West Virginia University School of Medicine. As a US Air Force Reservist he designs programs to promote healthier and better running with the US Air Force Efficient Running Project (program modules on website below). He has been a national-level Masters runner, having competed for over 35 years with more than 100 marathon and ultra-marathon finishes. Mark is a two time winner of the Air Force Marathon and has a marathon PR of 2:24. As well as being the race director of Freedom’s Run race series in West Virginia, Mark is director of the Natural Running Center, an education portal designed to teach healthier running. He is also the owner of Two Rivers Treads – A Center for Natural Running and Walking in his hometown of Shepherdstown, WV. For details, visit drmarksdesk.com

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