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View Full Version : Re: SUMMARTNormal gait: Are joint angle standard deviationslarger atma ximal joint angular velocities?



Ton Van Den Bogert
04-16-2003, 10:27 PM
Dr. Chris Kirtley wrote:

> I think this warrants a bit more discussion. The SDs are clearly smaller
> during periods of HIGH angular velocity in all the plots I have looked
> at - and the effect is most pronounced in the knee angle. Compare the

Chris,

In your plot, it looks like the SD is smaller on the slopes
of the curve, but I'm not sure if it actually is. SD is the
width of the colored area measured along the *vertical* axis.

It has been a while since I looked at gait, but I distinctly
remember plotting SD as a function of time and seeing peaks
at the times of highest angular velocity. I could not dig up
any data quickly, but you should be able to plot SD vs. time
and see what it looks like.

For normal gait, the timing variations between gait cycles may not
be sufficient to cause the increased SD on the slopes that was
described by At Hof and me. The knee joint may have a very
stable timing in normal gait.

Another thing that I noticed in your plot was a tendency for SD
to be higher when the angle is higher. This could be a result
of how the knee joint functions in gait. A 5 degree variability
in max flexion angle (which occurs in the swing phase) would not
cause problems, but if there is the same variability in the min
flexion angle (which is near neutral and occurs in stance), gait
stability would be seriously affected. So I can imagine that the
lower flexion angles are more tightly controlled.

Ton van den Bogert

--

A.J. (Ton) van den Bogert, PhD
Department of Biomedical Engineering
Cleveland Clinic Foundation
9500 Euclid Avenue (ND-20)
Cleveland, OH 44195, USA
Phone/Fax: (216) 444-5566/9198

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