In my post, TONGUE TIED, I described how a conventional ski boot tongue can block the glide path of the ankle during dorsiflexion, disrupting the physiology of the ankle joint. It is essential to avoid this especially in dynamic activities such as skiing because the ankle joint is a portal for the flow of neural information. Neural flow from the more than 200,000 nerve endings in each foot and mechanoreceptors in the ankle send a flow of proprioceptive, sensory information to the central nervous system where it is processed and used to generate postural responses that sustain balance. Disrupting the physiology of the ankle joint with physical structures can disrupt neural flow and introduce foreign forces into the ankle joint that contaminate neural information from mechanoreceptors. Disrupting the physiology of the ankle joint has a similar effect on the balance system as taking a hammer to your computer or smart phone then expecting it to still work.
My US Patent No. 4,544,299, published almost 30 years ago, discloses an in-boot tongue fit system that restrains the foot without obstructing the glide path of the ankle joint. The short video clip below shows a section through the center of the tongue system superimposed over the actual patent figures to illustrate how this system works when used in a conventional ski boot shell. The shank and forefoot portions are separate components joined by a flexible link. This allows the components to maintain their respective positions on the shank and forefoot during ankle flexion.
The in-boot system allows the ankle to flex while maintaining the position of the load centre on the shank. In order to keep the load on my shin centred in my Head World Cup boot work I had to perform some tongue surgery. The photo below is of the original tongue sectioned through the centre to reveal the core.
The first thing to note is the use of chip foam for the tongue padding. Chip foam is made from foam scraps that are ground up and held together in matrix with a bonding agent. It has been my experience that chip foam has very poor energy absorbing qualities. My first procedure will be a partial chip foamectomy. Since I only want the lower distribution of force on my shin to extend a little further below the load centre at the top of the front of the shaft than it extends above the load centre I don’t need any foam below this point where it could load my shin. I am also going to surgically remove a portion of the outer padded tongue skin since it is folded over adding thickness in the glide path of the ankle, the very place where I don’t want any foam or padding. While I am at it, I am going to remove all the chip foam from the forefoot of the tongue since it is next to useless anyway.
Here’s what the tongue looks like after removal of the foam.
In addition to removing the foam, I also trimmed off the front of the plastic tongue body that would normally be used to stitch the tongue to the liner. I want my tongue to be able to ‘float’ in the forefoot area to reduce any possibility of the transition blocking the glide path of my ankle joint. As my shin approaches the front of the boot cuff in the lead segment of flexion, I want to decelerate the movement as opposed to having my shin slam into the top edge of the shaft (aka Lange Bang). I also want to create more space below the pressure distribution zone to help maintain the centre of pressure while reducing the possibility of any load at the bottom of my shin that could block the glide path of my ankle. The solution? Add a band of foam to the tongue in front of my shin bone as shown in the photo below.
I don’t want to add foam to the entire area of the tongue. I only want to add a rectangular band of foam that is directly in front of my shin bone. The reason for this is that there is usually a gap where the sides of the liner overlap the sides of the tongue. Placing a band of foam in front of the shin bone draws the sides of the tongue inward as my shin pushes through the gap. This assists the deceleration of the forward movement of my shin during ankle dorsiflexion while helping keep the force centred. The photo below shows the gap.
When I am skiing, the only time I would ever have any perception of contact of my shin with the front of my cuff is if I were to get momentarily pitched forward. Even then, any sensation of any contact is minimal. When I am skiing, the only sensation I am consciously aware of is the considerable tension in the soles of my feet.
In my next post I will discuss final tongue modifications including how I reduce the crash space over my forefoot.