>>>This is the message I sent:
>>>
>>> I'm presently working on postural sway with head injured subjects.
>>>I'm having some troubles to find a way to quantify the surface of the sway.
>>>The results shown a multi-form pattern. Subjects have been tested on a AMTI
>>>force plate-form and the acquisition is done by the Peak system.
>>>
>>> Here are some responses.
>>>
>>>Thank you for the numerous responses !!!
>>>
>>>Mylene Dault
>>>
>>>*********************************************** ****************************
>>>
>>>
>>>I have the following references for you
>>>
>>>ACH Geurts et al. Arch Phys Med Rehabil 72, 1991,p 1059.
>>>
>>>Attention Demands in Balance...
>>>ACH Geurts et al. J of Motor Behavior 26(2), 1994, p 162.
>>>
>>>Identification of Static and Dynamic..
>>>ACH Geurts et al. Arch Phys Med Rehabil 77, 1996, p639.
>>>
>>>In this artikles they have done postural and balance studies.
>>>May be it will be a help for you.
>>>
>>>Rico
>>>"Rico de Visser"
>>>
>>>
>>>*********************************************** *********************
>>>
>>>
>>>
>>>Currently a graduate student I advise is working on postural sway using an
>>>AMTI force plate. To quantify the amount of sway he sums the amount of
>>>displacement of the ground reaction forces in the X and Y directions
>>>(lateral and fore/aft, respectively, according to AMTI's definition) during
>>>a five sec. trial with sampling at 100 Hz. For example if the there are five
>>>consecutive samples of 0.5, 0.10, 0.5, -0.5, -0.10 cm, for the X values he
>>>adds 0.5+0.5+0.10+0.5=2.5 cm (differences between the values). This is also
>>>calculated for the Y direction. The velocity can be determined by dividing
>>>by the amount of time to get cm/sec.
>>>
>>>The calculations for the difference between the 500 numbers can easily and
>>>quickly be derived using a spreadsheet like Microsoft Excel. If the X data
>>>is in column A (cells A1:A500) of the worksheet, enter the formula in cell
>>>B2: =ABS(A2-A1) and fill the formula down to B500. In cell B501, calculate
>>>the sum by entering the formula: =SUM(B2:B500) or by clicking on the sum S
>>>button on the toolbar.
>>>
>>>This is like an integration of a full-retified EMG signal. A
>>>root-mean-square (RMS) calculation would also work, I believe. If your Peak
>>>system is recording the force plate data, it should be able to export the
>>>files to a spreadsheet. We use an Ariel system which exports data into the
>>>
>>>I have not verified this method with other people studying postural sway and
>>>would be interested in knowing if this is a valid method. I would also like
>>>to see other responses you get. If you don't post replies, please forward
>>>them to me.
>>>
>>>Thank you.
>>>
>>>BE
>>>
>>>
>>>Bruce Etnyre, Ph.D., P.T. _/_/_/_/ _/_/_/_/ _/_/_/ _/_/_/_/ _/
>> _/
>>>Human Performance and _/ _/ _/ _/ _/ _/ _/ _/
>>> Health Sciences Dept. _/ _/ _/ _/ _/ _/ _/
>>>Rice University _/_/_/_/_/ _/ _/ _/_/_/ _/ _/
>>>6100 Main MS 545 _/ _/ _/ _/ _/ _/ _/
>>>Houston, Texas 77005 _/ _/ _/ _/ _/ _/ _/
>>>USA _/ _/ _/ _/ _/ _/ _/ _/
>>>etnyre@rice.edu _/ _/ _/_/_/_/ _/_/_/ _/_/_/_/ _/_/ _/
>>>(713)527-4058
>>>FAX: (713)285-5329
>>>*********************************************** **************************
>>>
>>>We resolved the problem as follow supposing you have about 1000 points
>>>passed by sway. All points have a pair of coordinates (x , y) :
>>>
>>>1. taking the average of x and y gives X0 and Y0
>>>2. calculate the distance D and the angle A of each point vs X0 and Y0
>>>3. divide the area in 24 sectors with X0 and Y0 as center
>>>4. sort the data so that you find which point is in wich sector
>>>5. sort the data in each sector to the biggest D
>>>6. calculate the surface of each triangle obtained and make the sum.
>>>
>>>The more sectors gives more chance to be accurate but also increase
>>>the chance of finding a area without points...
>>>
>>>I found the algorithm in :
>>>Arch. Phys. Med. Rehabil vol 75 September 1994
>>>
>>>Sincerely
>>>Pierre
>>>=============================================== ===========
>>>ing Pierre Van Cleven
>>>Dept of Kinesiology Institute of Physical Education
>>> University of Gent
>>>Watersportlaan 2 B-9000 Gent (Belgium)
>>>tel (32)9.264.63.21 fax (32)9.264.64.97
>>>=============================================== =========
>>>
>>>*********************************************** ********************
>>>
>>>>I'm having some troubles to find a way to quantify the surface of the sway.
>>>>The results shown a multi-form pattern.
>>>
>>>You might try looking at the data in terms of fractional brownian motion,
>>>as in these papers:
>>>
>>>Riley, M. A., Mitra, S., Stoffregen, T. A., & Turvey, M. T. (1997).
>>>Influences of body lean and vision on unperturbed postural sway. Motor
>>>Control, 1, 229-246.
>>>
>>>Collins, J.J. & De Luca, C.J. (1995). The effect of visual input on
>>>open-loop and closed-loop postural control mechanisms. Experimental Brain
>>>Research, 103, 151-163.
>>>
>>>About a dozen additional ways to characterize postural sway are presented in
>>>
>>>Riccio, G. E., & Stoffregen, T. A. (1991). An ecological theory of motion
>>>sickness and postural instability. Ecological Psychology, 3, 195-240.
>>>
>>>Good luck.
>>>
>>>Tom Stoffregen
>>>
>>>---------------------------------------------------------------------------
>>---
>>>Thomas A. Stoffregen, Ph.D.
>>>Department of Psychology, P.O. Box 210376
>>>University of Cincinnati
>>>Cincinnati, OH 45221-0376
>>>
>>>(513) 556-5569
>>>Personal homepage: http://ucaswww.mcm.uc.edu/psychology/Faculty/Stoffreg.htm
>>>Postural stability laboratory:
>>http://ucaswww.mcm.uc.edu/psychology/stoffregen/
>>>---------------------------------------------------------------------------
>>---
>>>
>>>
>>>*********************************************** ****************************
>>>
>>>
>>>Mylene:
>>>
>>>We are just developing a program for testing postural sway
>>>in knee patients. So far, we have the subjects stand on the
>>>force plate (Kistler) in a single leg stance for 15 seconds
>>>with eyes open and eyes closed. We record the vertical ground
>>>reaction force Fz and the location of the force vector on the
>>>platform in both directions (ax and ay). We sample 600
>>>measurements, i.e. we have a frequency of 40 Hz. We calculate the
>>>standard deviation of ax and ay, the range between min and max
>>>values in both directions and the total distance that the force
>>>vector "traveled" during the whole period. Dividing distance by
>>>time gives you something like the sway velocity.
>>>
>>>We have yet to find out which parameter(s) is (are) most reliable
>>>and can help to distinguish between normal and pathologic
>>>conditions. I hope this helps a little.
>>>
>>>Ciao,
>>>
>>>Dieter...
>>>
>>>__________________/\ ________/\ _____________________
>>>
>>> \/ \/
>>>
>>>Dr. Dieter Rosenbaum
>>>
>>>Abt. fuer Orthopaedische Physiologie (Kinesiology Lab)
>>>
>>>Klinik und Poliklinik fuer Allgemeine Orthopaedie
>>>
>>>Westfaelische Wilhelms-Universitaet Muenster
>>>
>>>Albert-Schweitzer-Str. 33
>>>
>>>D-48129 Muenster, Germany
>>>
>>>
>>>
>>>Phone: (...49) 251 - 834 7981 or 7995 (fax 7989)
>>>
>>>email: diro@uni-muenster.de
>>>
>>>*********************************************** ****************************
>>>
>>>
>>>Thank you to Stephen J. Kinzey, Ph.D. for his response.
>>>
>>>
>>>Stephen J. Kinzey, Ph.D.
>>>Assistant Professor / Director of Biomechanics Laboratory
>>>The University of Mississippi
>>>Department of ESLM
>>>University, MS 38677
>>>e-mail: skinzey@olemiss.edu
>>>http://www.olemiss.edu/~skinzey/biomch.htm
>>>office: (601) 232 - 5540
>>>fax: (601) 232 - 5525
>>>
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