Average Cop velocity vs. walking speed

[Petcu Daniel]

Dear Members,
Because at the moment I don’t have a system for measuring the walking speed I would like to use as reference the average velocity of centre of pressure as measured by a force platform. Is the average velocity of centre of pressure as measured by a force platform a good predictor of the walking speed ? What could be wrong if I’ll use, for example, the average Cop velocity to select between walking trials ? Till now I’ve one reference related to my problem (Keijsers et al.: Velocity of centre of pressure as a predictor of walking speed. Journal of Foot and Ankle Research 2012 5 (Suppl 1):O28.) There are any other literature related to this subject ?
Thank you in advance for your kindness,
Respectfully,
Daniel

[Ross Miller]

Re: Average Cop velocity vs. walking speed

Hi Daniel,

If you have the GRF over a complete gait cycle (or if you have it for just one foot but can reasonably assume bilateral symmetry) and the mass of the subject, then you can calculate the speed of the CoM from just the force platform data.

See this thread for some discussion on doing this:

http://biomch-l.isbweb.org/threads/23216-Kinetic-measurement-of-the-centre-of-mass

Hope this helps,
Ross

[Petcu Daniel]

Re: Average Cop velocity vs. walking speed

Hello Ross,
Thank you for your reply! I'm interested by the free moment and my data, in a " visual analysis" way doesn't indicate to me a bilateral symmetry. The GRF components seems to show a bilateral symmetry so, how it is correct to define, in my case, the bilateral symmetry: from the GRF perspective or from the free moment one ?
Respectfully,
Daniel

[Vipul Lugade]

Re: Average Cop velocity vs. walking speed

Daniel,

You might also be interested in the following article: http://www.sciencedirect.com/science...66636214006171

Though there is no comparison made to walking velocity, this might give you a quick look at how the COP velocity changes throughout stance and among different foot positions.

Take care,
Vipul

[Ross Miller]

Re: Average Cop velocity vs. walking speed

Hello Ross,
Thank you for your reply! I'm interested by the free moment and my data, in a " visual analysis" way doesn't indicate to me a bilateral symmetry. The GRF components seems to show a bilateral symmetry so, how it is correct to define, in my case, the bilateral symmetry: from the GRF perspective or from the free moment one ?
Respectfully,
Daniel

If you're assessing symmetry visually (I assume you mean you're just plotting the GRF and free moment and looking at them, which is fine), then you must have force plate data for both the left and right foot? In that case there's no need to make any assumptions about symmetry, you have all the data needed to calculate speed without that assumption.

Ross

[Petcu Daniel]

Re: Average Cop velocity vs. walking speed

If you're assessing symmetry visually (I assume you mean you're just plotting the GRF and free moment and looking at them, which is fine), then you must have force plate data for both the left and right foot? In that case there's no need to make any assumptions about symmetry, you have all the data needed to calculate speed without that assumption.

Ross

Hello Ross,
I have data from left and right foot but, unfortunately I have only one force platform ! So the data from the left and right foot are from different trials.
But, this "technical situation" is raising to me a theoretical question for which I've need help: what could be wrong if I'll use the averageVCoP for selecting the gait cycles? For example, instead of "average walking speed +/-10%" to use "averageVCop +/- 10%".
Thanks for your help and patience !
Respectfully,
Daniel

[Petcu Daniel]

Re: Average Cop velocity vs. walking speed

Daniel,

You might also be interested in the following article: http://www.sciencedirect.com/science...66636214006171

Though there is no comparison made to walking velocity, this might give you a quick look at how the COP velocity changes throughout stance and among different foot positions.

Take care,
Vipul

Dear Vipul,


Thank you for the reference! I think the same question is valid for this work also: if you don't report the walking speed, how do you know that the registered differences are not the result of the differences in walking speed? The three force plates has registered the COP trajectory for the same foot in the same trial ?


Sincerely,
Daniel