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Interpreting Your Balance Test Metrics

Just last fall, we released a new test for AlphaPWR accessible via the remote control, namely our balance test. While things like this are generally confined to advanced facilities and used only by people in lab coats, we've taken a more user-centric approach.


Our balance test is so simple anyone can use it, yet some of the resulting analytics can be a bit hard to understand on first sight. Therefore, I'll try to explain as best as I can here.


Whether you choose to do the test on the left or right foot, with eyes open or closed, or for 5 or 60 seconds, the same result screen is displayed.


Score

As you take your first look at the result screen after a balance test, you'll notice we've chosen to make one metric stand out above all others.

The top part displays score in huge font size, which is a metric based solely on area. We created this derived measure to give an accessible and easily comparable impression of the user's "overall" performance in the test. There are many specifics one could drill into, but we've found area to be a good measure in most cases.


But what does area mean in this context? Well, throughout the test, as the user wiggles and adjusts their body to stay in the same spot, we measure a continous point of pressure on the surface of the forceplate. The movement of this point is what is displayed as a squiggly white line in the top right (we'll get to the gold line later).


Looking at the squiggle plot, you can also see a dotted trace enclosing the pressure line. This is the figure we measure the area (as well as circumference) of. As the user moves away from their average point of pressure (displayed as a white cross in the plot) throughout the test, the area naturally increases.


Pressure and mass

As you can see in various instances on the result screen, we display both a white and a gold line. In the bottom, the coloration is briefly pointed out as denoting center of pressure (COP) and center of mass (COM). I'll refer to these simply as COP and COM going forward.

COP (as mentioned previously) is what we measure directly using the forceplate, and represents the point at which your body is balancing in any given moment. This is in itself a perfectly good measurement for assessing your balance, but we decided to take this one step further.


As you can see, the COP quickly moves around to keep your body balanced, and we wanted to show something that represents your body in this context. A good measure that represents your body in any given exercise on a forceplate is mass, specifically the centre of it, i.e. COM. We can directly measure where your COM is vertically, but in the horizontal plane this is a bit more tricky.


To keep this artivle at a somewhat readable length, I won't go too much into detail on the specifics of the conversion here, but for COM estimation we apply a low-pass filter to the COP data. This basically means "dampening" the rapid peaks, which if you think about it makes sense if you think about COP as the point at which the COM is balancing.


Graphs

Moving on from the top part of the report, we have three graphs that showing how some metric changed throughout the test. These can give some insight into what went into your overall score, both good and bad. They are also accompanied by their own "mini scores".

The deviation graph shows how far you were away from the average COP (white cross in top right plot) at any given point. It's accompanying mean value (displayed both by value and a solid white line) tells you your average distance to the COP. The dotted line represents average COP, and it is in this case at the bottom because deviation is an absolute measure, meaning you always have more than or equal to 0 distance to the COP.


Left-to-right and Back-to-front both show directional COP movement. These could be used to easily assess where any problems in a users balance lie. They also both display range which is the total directional distance between extremes, i.e. for left-to-right it is the horizontal distance between the leftmost and rightmost points. As with the deviation graph, these also display a dotted line representing average COP.

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