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



jbdingwell38
04-17-2003, 04:39 AM
Chris (& others):

I'm sorry, but I'm going to have to agree with Ton van den Bogert and At
Hof on this one.
Moreover, I have plotted some of my old dissertation data that shows this:
http://www.edb.utexas.edu/faculty/dingwell/SD.jpg

The reason that the SD's look smaller during periods of high velocity is on
a plot of mean +/- SD is an optical illusion. The SD band appears narrow
(horizontally), but if you actually measure (vertically), you get a
different answer....

The figure shows data from a healthy young subject walking over level
ground. The joint angle data were obtained with goniometers (P&J) and the
mean +/- SD curves were constructed from a set of 50 consecutive strides
from the middle of the self-selected speed walking trial. Even though the
SD bandwidth appears narrower in the mean+/-SD plots (top plots), the SD
values get larger when angular velocity is higher (bottom plots).

Although I have made no attempts to verify this, I believe Ton's suggestion
as to why this happens makes a lot of sense.

I hope this helps.....
Jon Dingwell


At 08:27 AM 4/17/2003 -0400, Ton van den Bogert wrote:
>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



Jonathan Dingwell, Ph.D., Assistant Professor

University of Texas at Austin
Department of Kinesiology and Health Education
1 University Station, D3700
Austin, TX 78712-0360

Phone: 512-232-1782 *** NEW PHONE NUMBER !!! ***
Lab: 512-471-4017
Fax: 512-471-8914
Web: http://www.edb.utexas.edu/faculty/dingwell/

"Sanity is the playground for the unimaginative" -- Anonymous bumper sticker

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