In physical therapy school in 1990, I came to understand balance from two vantage points. The first was the control of the body and its center of mass over the surface area of the feet and the space between the feet. The second was from a more “refined definition” based upon neurophysiology and physics. Balance was the ability of the organism (nervous system) to adapt to the changing conditions of the body and environment to maintain the intended sitting, standing or other desirable posture. I am paraphrasing and synthesizing of course after 30 years of practice. That though is what stayed with me over the years. My "takeaway" from my formal education in the 1990’s, and reinforced with my terminal degree in 2006. This was primarily a function of kinesiology education with some neurophysiology, physics and advanced physiology thrown in.
My work with Rehabit Health to develop the balance, gait and selective exercise retraining technology would clarify the very nature of how I viewed human balance and most importantly restoration of balance and walking. It was this work in which I coined the term “balance field”. Since I regularly bandy that label about, and I inevitably am met with a blank look a majority of the time, I decided it was time for me to explain what exactly I mean by the term “Balance Field” or more precisely, “Human Balance Field”.
When I Google the terms as recently as 08-13-2023, there is nothing in the images or otherwise that I can find that describes this “Field” at least not in the way I understand it. Since it is not described in the manner in which it appears to exist, the implications for meaningful, and significant recovery would be arguably “elusive”.
I have written that in the early years, the technology focused on restoration of the gait cycle. As the clinician and the only member of the Rehabit Health team with formal education on the nature of balance, I argued that unless balance and understanding its attributes were explored, the technology would not be as effective as we all desired. Walking is after all, a form of balance. Without balance there is no walking. Now that resources were put into the question of human balance, I fell back on that 1990 definition. It made sense on a lot of levels. It was simple. It was Newtonian physics, and at least for inanimate objects, irrefutable. The question was though, did the definition really apply to people?
In getting started, the Center of Mass(COM) or predominate weight of the person was available to generate from a technology standpoint. For insoles this is sometimes referred to as Center of Pressure. I will though refer to the “predominate weight or pressure” from this point forward as the Center of Mass(COM). So, going into the trenches, the first question in terms of balance and rehabilitation of it was “ what are the boundaries of balance for a person with normal balance?” I really did not know. So, I started with the premise of the base of support of a given person. The surface area of the shoes(feet) and the space between them. By definition and clinical inference, this seemed to be a close and a natural starting point.
This illustration was the starting point. It is the definition
I learned in kinesiology training as an undergraduate and seemed to be generally what I experienced.
Figure 1
It soon became apparent though that the area in which the Center of Mass(COM) interacted upon was not based on this definition. Not even close. I decided that I would instead continue to “explore” what was accurate by using a round target. This was in part to ensure a degree of safety, so the target was defined by a universal color scheme. Red was “danger” or the outer limits, Yellow represented “proceed with caution” and white the “safe zone.”
This was an early compromise because it was safe to train. The problem was it discouraged unilateral standing or standing on one foot. Furthermore, it seemed unlikely to determine what the boundary of balance or the “field” was.
Figure 2
Resources being what they were, I had to merely do what was possible and reasonable. I had to make some inferences and because I could test this on myself, the engineer, other family members and eventually patients, the boundaries and very specific parameters could be “discovered.” The results of the testing were unexpected and frankly fascinating. The balance area is “squarish” in nature and corresponds to 2 of the 5 key anatomical landmarks of the foot.
The Area of Balance which I early on defined as the area in which the COM moves and interacts was a square in which the boundaries were the 3rd metatarsal heads and the calcanei (heels). The COM does not really move beyond these boundaries except in extreme circumstances, and for most people with normal balance, moving beyond them would cause loss of balance
Figure 3
Over time, it occurred to me that the COM interplay and the Base of Support might actually look like this. See figure 4 below.
The area of balance which I gradually started referring to as “the Field of Balance and eventually the “Balance Field” appeared very much to have a larger base (illustrated by the blue highlights) for which the individual’s COM interacted on a more limited “Top” region (the non-highlight area). However, for all practical and rehabilitative purposes, the “Balance Field” was as illustrated in Figure 3.
Figure 4
Now what is obvious to the observer is that the feet are not always neatly, side by side. This is very true. So, if the shape of the field changes and possibly even continuously changes, should we not try to capture that? The short answer was maybe(?). So employing the power of trial and error, the engineer and myself with some friends and family volunteers explored this question. The static side by side representation though proved valid irrespective of the position of the feet, and with use of “zones”, unilateral standing or standing on one foot did not affect the retraining.
This was a relief for a few reasons. First, the amount of software programing to adjust the field dimensions would be overwhelmingly complicated. Second, the potential sensory overload for patients having to look at and interpret a continuously changing field was a real concern (especially for neurological patients).
As time and testing continued, it was clear that there were three distinct “zones” within the balance field that were relevant to balance recovery.
See Figure 5 below:
Zone 1: This area of the Balance field is defined by 30 to 70% of the “weight” COM on both feet.
Zone 2: Noting a left and right zone 2. In this region there is 71 – 89 % of “weight” (COM interplay) on either the left or right zone. And a corresponding 11 – 29% of “weight” residually upon the opposite foot.
Zone 3: Noting a left and right zone 3. In this region there is 90 - 100 % of “weight” (COM interplay) on either the left or right zone. And a corresponding 0 - 10% of “weight” residually upon the opposite foot.
Figure 5
By 2021 the “Balance Field” had its boundaries defined, COM interplay “zoned” and was one of two major components practically utilized to restore impaired balance. Fortunately, and I do mean this, the mechanism was a classic example of “K.I.S.S.”( keep it simple stupid). While there is without question deep complexity in terms of human physiology, attitudinal and cultural factors in terms of rehabilitation in general, at least there was clarity on one of the fundamentals of clinical rehabilitation of standing balance.
Presently the Human Balance Field is defined as the area comprising the feet and space between the feet in which the boundaries comprise a square shape extending from the heels to the 3rd metatarsal head of both feet. This is the field in which the individual’s COM or predominate weight ideally is able to easily interact to allow all static and dynamic standing balance activity including walking.
One might take note of the fact that I said “one of the fundamentals”. I also eluded to “one of two” major components. The purpose of this week’s blog was to cover the first of the two major facets of balance recovery, namely the concept of the Balance field, its boundaries and definition. The discussion though is not complete without a presentation of the second major element of balance recovery. That will be the topic of next week’s blog.
Warm Regards
Dr Michael J. Malawey, PT
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