A good segue to continuing my discussion of the SR Stance is to provide a tool that will enable the assessment of the effect of different surface densities and textures and footwear, orthotics and generic insoles on the small nerve proprioceptors in the plantar foot.
Most people assume that cushioning under the plantar foot is a good thing; that it provides comfort and helps protect the foot from shocks. Who needs footbeds? Everyone. It’s only common sense. Everyone knows the foot is weak. It needs support. Except, that none of this is true.
“With thousands of plantar receptors, the foot is also a proprioceptive-rich structure, containing thousands of small nerves that are sensitive to every subtle movement we make. Our ability to walk, run or jump is all initiated through stimulation of these nerves on the bottom of the foot (aka the plantar foot).
“Because of the smaller diameter these plantar nerves are able to send signals faster to the Central Nervous System, creating faster response times”.
– Barefoot Strong by Dr. Emily Splichal
“80% of our plantar proprioceptors are sensitive to vibration” – Nigg et al
“With small nerve receptors sensitive to stimuli such as texture, vibration, pressure and skin stretch, the skin on the bottom of the foot is unique when compared to the skin on the top of the foot or the lower leg.
“As soon as we put on socks, orthotics or shoes we block these highly sensitive small nerves on the bottom of the foot.”
– Barefoot Strong by Dr. Emily Splichal
What Dr. Splichal says is true of any form of arch support. Ski boots are arguably the worst form of footwear for blocking the highly sensitive small nerves on the bottom of the foot.
As Dr. Splichal explains, the power of neuromuscular activation that enables precise balance and movement originates from the ground and moves upward through the plantar foot.
An easy way to impart an appreciation of how the stability, density and texture of surfaces under the plantar foot or structures such as insoles, orthotics, ski boots, liners or any form of footwear, affect stance, balance and movement patterns is by doing a series exercises on one foot starting barefoot on a hard level, stable surface, then adding different materials between the plantar foot and the supporting surface and assessing their effect on balance.
Dr. Splichal demonstrates a series of exercises in her EBFA YouTube Fitness group called Best Surfaces for Barefoot Training – https://youtu.be/gvJjIi3h1Bs
There are some issues with the quality of this particular video, especially as it ends and the volume increases dramatically. So use caution, especially if you are wearing earbuds or headphones. This issue aside, Dr. Splichal’s demonstration is spot on.
The reference surface for establishing a baseline should be solid, stable, level and uniform. Texture is important. The worst surfaces for small nerve stimulation are smooth and glass like. Through experimentation, I have found that the best surface in my home is the concrete floor in the mechanical room which is coated with an epoxy paint with fine sand imbedded in it. The worst surface is the smooth laminate in the main living area. Tile in the entry hall with a slight texture is somewhere in between.
The photo below shows textured surface concrete on the left, smooth laminate on the right.
Balancing on One Foot
Although balancing on one foot in a process of alternating single limb support is our basic mode of locomotion, most people seldom engage in prolonged balance on one foot. In order to ensure accurate assessment of surface effect, the move from balance on two feet to balance on one foot should be rehearsed. In my patents, I refer to these two states as bipedal and monopedal support.
Start by standing relaxed on both feet in an upright stance. Start moving the pelvis towards one foot. The movement of the pelvis should be in an arc that is sideways and forward as if the side of the pelvis on the support leg is moving diagonally towards the little toe.
As the pelvis moves forward, relax the ankle and allow the weight (pressure) to move to the ball of the foot. Keep a small bend in the knee as Dr. Splichal advises in her video.
Move back to balancing on two feet. Then repeat the balance exercise on the other side.
Repeat the exercise until you can quickly find stable balance on each foot and maintain it with minimal effort for at least 20 seconds. This may take time if the muscles that are being recruited are weak and/or unbalanced.
When you are comfortable balancing on either foot, try the exercise on different stable, hard surfaces and compare the effect of the different surface textures on balance.
You may want to try the same exercise on carpet if it is available.
A Word about Pronation
A campaign of misinformation has created a widespread perception that any amount of pronation is unnatural, even dangerous and should be prevented with a supportive insole or orthotic. Some experts have taken the position that a small amount of pronation is desirable but that it should be restricted to a specific amount controlled by an orthotic.
In a future post, I will expand on my earlier discussions of the 3 foot types. While it is correct that both pronation and supination are abnormal, the context of abnormal is in bipedal stance. From a perspective of basic trigonometry, the leg must adduct (move towards center of the body) about 6 to 7 degrees in order for the foot to be positioned under the centre of gravity. The foot must rotate an equivalent 6 to 7 degrees about its long axis in order for its tripod points to become compliant with the supporting surface. STJ joint coupling produces an equivalent amount of internal rotation of the tibia about its vertical axis. Eversion/internal rotation is called pronation.
The absurdity of what amounts to an all out war on pronation should become apparent from viewing the stick man figure below from my patents.
Systematic efforts aimed at immobilizing the joints of the foot and leg in the ski boot, usually in neutral STJ, prevent skiers from assuming a balanced (read: pronated) position on the outside foot and ski ski thus ensuring the existence of an unbalanced moment of inversion/external rotation force. In addition, studies have shown that restraining the ankle in a tightly fitting ski boot increases laxity of the knee under closed chain whole leg rotation by approximately 30% over lesser forms of ankle constraint.
In my next post, I will discuss a series of exercises for assessing the effect of the components of the ski boot, including different liner components and interventions that support the arch of the foot.
Dr Emily Splichal is a Podiatrist and Human Movement Specialist.
She is the Founder of the Evidence Based Fitness Academy (EBFA) and Creator of the Barefoot Training Specialist, Barefoot Rehab Specialist and Bare Workout Certifications for health and wellness professionals.
Her book, Barefoot Strong is available in print and ebook formats.