Hello Amirhossein

Fay Horak and Martina Mancini have been looking at this for the past few years with accelerometers. They calculate frequency based parameters as well as Jerk (rate of change of acceleration) and Root Mean Square (RMS: magnitude of acceleration). Google their names along with Balance and you'll easily find their work. Moreover, my colleague Silvia Del Din (Newcastle University) has done some nice analysis recently investigating how the above parameters change over the course of a standing balance assessment: Del Din S, Godfrey A, Coleman S, Galna B, Lord S, Rochester L. Time-dependent changes in postural control in early Parkinson's disease: what are we missing?. Medical & Biological Engineering & Computing 2015.

Papers by Martina and Silvia should give you a good insight how to calculate what you need. 

Hope that helps

Alan

Hi Amirhossein,

To add to Alan contribution you could also check the following article about some mathematics use to calculate sway (and others) parameters :

Prieto, T. E., Myklebust, J. B., Hoffmann, R. G., Lovett, E. G., & Myklebust, B. M. (1996). Measures of postural steadiness: differences between healthy young and elderly adults. Biomedical Engineering, IEEE Transactions on, 43(9), 956-966.

Hope this helps,

Michel

Have a previous article, that can help:

Some methods and parameters of body sway quantification and their neurological applications

A. Hufschmidt, J. Dichgans, K. -H. Mauritz, M. Hufschmidt

Best regards.

Dear friends

we use a posturography setup. we have the information of displacement of center of pressure in medial lateral and anterior posterior during the testing time in separated graphs  and we need to calculate body sway as it has been frequently reported in stability papers or other parameters from it which are related to postural balance and steadiness.

now we don't know how to extract these parameters form those information.

for example its standard deviations or mean or peak amplitude or first and second differentiation what are the mechanical meaning of these parameters and which one is body sway 

best regards

Amirhossein

David A. Winter has a very useful go-to-guide on all this stuff: Biomechanics and Motor Control of Human Movement. Or even his review on: Human Balance and postural control during standing and walking (1995). Be careful on what you interpret as balance though: CoP, COM etc are terms that have been incorrectly interchanged and assumed to be the same!

Martina Mancini's paper: iSway from Journal of Neuroengineering and Rehabilitation, 9:59, 2012 will help with what you need. Specifically Table 2 within that paper. (Use of frequency, sway and Jerk may also be estimated from force plates, I presume thats what you are using so you will need to adapt accordingly). 

Happy reading

Alan

thank you dear Alan would you plz give me your email for more contact?

hi Amirhossein

feel free to message me via ResearchGate

Hi Amirhossein,

I`m not sure that I understand exactly what kind of data you need, but you can check if Sway Analysis Module software from Tekscan could be useful for your research.

Dear Alina 

we don't need a setup for posturography we have a Synapsys posturography setup and it provides us with data of the center of pressure in medial lateral and anterior posterior we need to know how to calculate the body sway and other balance parameters from our data

Hi Amirhossein,

From displacement of COP you can extract several variables to describe/evaluate postural/stability control. However, it is not easy to relate these variables to physiological mechanisms. A summary of these variables and related references can be found in Vieira et al., 2015. Effects of four days hiking on postural control. PlosOne. 

dear Marcus

what are the limitations of relation these CoP parameters and physiological mechanisms.

Hi,

in our research we always related STD (standard deviation) as a body sway (mean body sway). So you can just calculate standard deviation of COP position in AP and ML direction. But it could be affected if you have some time trends in behaviour of your signal. The simplest is unidirectional time trend (let say that body move slowly forward during time of observation) than we use regression line, and as a mean body sway we calculate standard deviation in relation to this line.

If you check some of our papers about balance, LOS there is a lot of useful information.

Best

Greg

Article Evaluation of the Limits of Stability (LOS) Balance Test

I think a commonly cited paper in the calculation of CoP-based measures of postural stability is Prieto 1996 which provides a list of several measures of postural stability as well as their equations for calculation.  It should be noted that these are measures of CoP and not true measures of sway.