Orthotics are the fingerprints of running, in theory no two should be identical. As for the manufacture of orthotics, opinions vary wildly on how to make a “correct” orthotics.
In my opinion, the two critical areas of disagreement regarding orthotics are: casting technique and construction.
1. Casting Technique: Weight bearing or non-weight bearing?
Non-weight bearing casting has been popularized by podiatrists and involves placing the foot in a “sub-talar neutral” position, and basing the orthotic prescription on this.
Weight bearing casting places the foot in a deformable material or on a scanning device and taking multiple measurements to calculate the correct prescription.
Which technique is best? Both techniques have limitations. Sub talar neutral is a position that the foot may or may not achieve during normal foot movement; if it does move into this position, it is only for a very limited time during the gait cycle. That is, you are placing the foot into a position that may not represent true function. Weight bearing casting is more functional in that it does show the actual foot position. The corrections however are based on what is assumed to be optimal from the information obtained from the cast or scan. As you can see both methods make some assumptions regarding what is best for your foot.
2. Construction: Rigid or flexible?
To understand this issue, remember that the foot has to have multiple functions. It has to act as a flexible structure to adapt to uneven terrain, a rigid lever able to propel us forward, and a shock absorber that has to deal with impacts of 5G’s while walking and up to 8G’s when running.
My opinion for runners is that flexible is the way to go. It allows for normal foot function and the added capability of enhanced shock absorption if the orthotic has viscoelastic materials built into it. The other and perhaps most important element of a flexible orthotic is that it can stimulate joint receptors which creates a proprioceptive response in the cerebellum. That is, the part of our brain concerned with coordinated movement receives better quality information from the foot, which enhances muscular control and neurological function of the gait cycle. Our gait becomes more efficient.
Rigid orthotics tend to crutch the foot in one position, which denies it the ability to operate in a fully functional manner and reduces its shock absorbing capability. Proprioceptive response is also altered, but in a negative sense since the joint receptors that are normally stimulated with joint movement provide less information for neural processing.
Overall, my preference is for a flexible orthotic that is based on a weight bearing cast or scan. These tend to be a more functional device and result in fewer problems for the athlete as far as joint stress and adaptation time are concerned and offer up enhanced biomechanical efficiency that can and usually does translate into better performances.
[...] Dr. Miller on Orthodics article/post categories: running(t) , Injuries(t) November 15 2005 November’s article is the second in Dr. Miller’s two-part series discussing Pronation, Supination and Orthodics. It’s a great read that you can check out here. Bookmark this article on:These icons link to social bookmarking sites where readers can share and discover new web pages. [...]