Thanks to all who replied to my problem about balance and feet position.

Special thanks to Ambarish Goswami. I found his work most applicable to the

problem at hand.

Regards

Rene Ferdinands

Department of Physics and Electronic Engineering

University of Waikato

Hamilton 2001

New Zealand

--------------------------------

ORIGINAL EMAIL

--------------------------

Hello, I am a biomechanist specialising in the biomechanics of cricket. At

the moment I am studying the role of footwork in batting. Of particular

importance to a good batsman is the ability to use his footwork in order to

optimise balance. The question of balance and footwork in cricket has not

been objectively dealt with in the past - current theories are mostly

subjective, and not based on sound biomechanical principles. I am not sure

whether this is the case in other ball sports.

So my problem is the following:

"How can one quantify balance? Obviously, the area of the base of support

and the position of the centre of gravity in relation to it is a

fundamental concept. But how can this be quantified? Also what about the

types of base of support and their stability in relation to perturbations

from various angles?

For example, if one adopts a stationary posture with splayed feet, what

kind of perturbation forces is he more able to withstand than if he stood

with the feet straight or even pigeon-toed? Or what if one foot is straight

and the other splayed? (This can be the case in batting postures.) In other

words, how does the postion of the feet in relation to the direction of a

perturbation force effect balance. For example, if one considers the type

of posture that is best to withstand a front-on tackle in rugby, then what

about the angles of the feet in relation to the direction of the impact

force - which way should they point? - e.g. perpendicular/parallel etc to

the line of impact force ? What kind of calculations can quantify this? Is

there current biomechanical research that can deal with this problem? "

If you believe you can help me in this area, then a detailed reply would be

most appreciated.

Thank you.

Rene Ferdinands

Department of Physics & Electronic Engineering

University of Waikato

Hamilton 2001

New Zealand

---------------------------------------

SUMMARY OF REPLIES:

************************************************** **********************

It might be worth sking my French friend , D. P-M Gagez at

pmgagey@club-internet.fr

He is president of the posturological society (but not much cricket is

played in Paris !)

--

Geoffrey.Walsh@ed.ac.uk

http://www.ed.ac.uk/~gwalsh

Phone (0)131.664.3046

64, Liberton Drive,

Edinburgh

EH16 6NW

UK

************************************************** ***********************

Hi Rene,

You can use a pressure mat and collect foot pressure distribubtion. From

the mat, you can then obtain center of pressure trajectory and calculate its

length and area of travel, and this with respect to time.

If you wish more information, email or call me at 1-800-248-3669 ext 263.

You can also visit the following web site:

http://www.tekscan.com/medical/system_matscan.html

There is much research done in Europe (mostly in french) that deals with

posture and balance.

The research does indicate a relationship between normal able-bodies vs

pathological conditions with respect to center of pressure trajectory,

length and area of travel.

Hope this helps,

norman

Norman Murphy, Ph.D.

************************************************** **********************

Dear Rene,

G'day. I just had a teach-in on this topic on the Clinical Gait Analysis

list/website:

http://guardian.curtin.edu.au/cga/teach-in/bos

I have developed a BodyBuilder model which calculates the discrepancy

between the base of support and the centre of mass. Of course, most of

the time the latter is contained by the former, but not always - e.g. in

gait there are two periods each gait cycle when the CoM goes outside the

BoS, as you can see on the page.

Hope this helps!

Best wishes,

Chris

--

Dr. Chris Kirtley MD, PhD

Assistant Professor

Department of Rehabilitation Sciences

The Hong Kong Polytechnic University

Hung Hom

Hong Kong Special Administrative Region of the People's Republic of

China

Tel.: +852 2766 6755 Fax +852 2330 8656

************************************************** **********************

Hello Rene:

Please see my recent paper on postural stability of biped

robots (the concepts are quite relevant to the human). You

can download the paper from:

http://www.cis.upenn.edu/~goswami/papers/paper.html

The paper is:

Postural stability of biped robots and the foot rotation

indicator (FRI) point

A. Goswami

International Journal of Robotics Research, Vol. 18, No. 6, 1999.

If you have any question, I will be happy to answer. My work

in this area continues.

Ambarish Goswami

************************************************** *******************

>So my problem is the following:

>

>"How can one quantify balance? Obviously, the area of the base of support

>and the position of the centre of gravity in relation to it is a

>fundamental concept. But how can this be quantified? Also what about the

>types of base of support and their stability in relation to perturbations

>from various angles?

>From an instrumental approach, we have looked at several ways to assess

balance and postural sway. We have used three methods; force plate,

accellerometers, and motion analysis.

Motion analysis turned out to be the least sensitive of the three.

Force plates are the most conventional method of balance. A force plate is

a large plate (aluminum), that has force sensors in the four corners. The

subject stands in the center of the force plate, and any change in balance

(sway) is picked up by the sensors. When the subject is in balance (no

sway), the forces on the sensors will be equal (or will have reached a

static steady state).

Another way to measure balance is by attaching accelerometers to either the

subjects head or in the region of the C7 vertibra. The accelerometer picks

up motions of the head as the subject tries to maintain an upright

position. I've got some pictures on my web page at

http://www.ecn.ou.edu/~major/www/accel.html .

With either the force plate or the accelerometer method, one can easily

reduce the data (say for a 10 second trial) to a single number. There are

a number of statistical methods to do this, but the easiest (for us) was to

calculate the RMS (root-mean-squared) value for the entire 10 second trial.

The voltage produced by the accelerometer (or force platform) was recorded

via a digital-to-analog board every 1/100 of a second, and stored on the

hard drive as an ascii file (10,000 entries for a 10 second trial).

To calculate the RMS number, the values in the ascii file were all squared.

These numbers were all added up and divided by 10,000 (to calculate the

mean), and the square-root of this number was taken. This gives a single

number corresponding to the total amount of postural sway for the interval

of the trial.

Trying to condense everything down to a single e-mail message, I may have

overlooked or not explained something very well. If you have any

questions, please feel free to post back and I will do my best to help out.

Dan Major

Univ. of Okla. School of Industrial Engineering

major@ou.edu htp://www.ecn.ou.edu/~major

************************************************** ***********************

---------------------------------------------------------------

To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl

For information and archives: http://isb.ri.ccf.org/biomch-l

---------------------------------------------------------------

Special thanks to Ambarish Goswami. I found his work most applicable to the

problem at hand.

Regards

Rene Ferdinands

Department of Physics and Electronic Engineering

University of Waikato

Hamilton 2001

New Zealand

--------------------------------

ORIGINAL EMAIL

--------------------------

Hello, I am a biomechanist specialising in the biomechanics of cricket. At

the moment I am studying the role of footwork in batting. Of particular

importance to a good batsman is the ability to use his footwork in order to

optimise balance. The question of balance and footwork in cricket has not

been objectively dealt with in the past - current theories are mostly

subjective, and not based on sound biomechanical principles. I am not sure

whether this is the case in other ball sports.

So my problem is the following:

"How can one quantify balance? Obviously, the area of the base of support

and the position of the centre of gravity in relation to it is a

fundamental concept. But how can this be quantified? Also what about the

types of base of support and their stability in relation to perturbations

from various angles?

For example, if one adopts a stationary posture with splayed feet, what

kind of perturbation forces is he more able to withstand than if he stood

with the feet straight or even pigeon-toed? Or what if one foot is straight

and the other splayed? (This can be the case in batting postures.) In other

words, how does the postion of the feet in relation to the direction of a

perturbation force effect balance. For example, if one considers the type

of posture that is best to withstand a front-on tackle in rugby, then what

about the angles of the feet in relation to the direction of the impact

force - which way should they point? - e.g. perpendicular/parallel etc to

the line of impact force ? What kind of calculations can quantify this? Is

there current biomechanical research that can deal with this problem? "

If you believe you can help me in this area, then a detailed reply would be

most appreciated.

Thank you.

Rene Ferdinands

Department of Physics & Electronic Engineering

University of Waikato

Hamilton 2001

New Zealand

---------------------------------------

SUMMARY OF REPLIES:

************************************************** **********************

It might be worth sking my French friend , D. P-M Gagez at

pmgagey@club-internet.fr

He is president of the posturological society (but not much cricket is

played in Paris !)

--

Geoffrey.Walsh@ed.ac.uk

http://www.ed.ac.uk/~gwalsh

Phone (0)131.664.3046

64, Liberton Drive,

Edinburgh

EH16 6NW

UK

************************************************** ***********************

Hi Rene,

You can use a pressure mat and collect foot pressure distribubtion. From

the mat, you can then obtain center of pressure trajectory and calculate its

length and area of travel, and this with respect to time.

If you wish more information, email or call me at 1-800-248-3669 ext 263.

You can also visit the following web site:

http://www.tekscan.com/medical/system_matscan.html

There is much research done in Europe (mostly in french) that deals with

posture and balance.

The research does indicate a relationship between normal able-bodies vs

pathological conditions with respect to center of pressure trajectory,

length and area of travel.

Hope this helps,

norman

Norman Murphy, Ph.D.

************************************************** **********************

Dear Rene,

G'day. I just had a teach-in on this topic on the Clinical Gait Analysis

list/website:

http://guardian.curtin.edu.au/cga/teach-in/bos

I have developed a BodyBuilder model which calculates the discrepancy

between the base of support and the centre of mass. Of course, most of

the time the latter is contained by the former, but not always - e.g. in

gait there are two periods each gait cycle when the CoM goes outside the

BoS, as you can see on the page.

Hope this helps!

Best wishes,

Chris

--

Dr. Chris Kirtley MD, PhD

Assistant Professor

Department of Rehabilitation Sciences

The Hong Kong Polytechnic University

Hung Hom

Hong Kong Special Administrative Region of the People's Republic of

China

Tel.: +852 2766 6755 Fax +852 2330 8656

************************************************** **********************

Hello Rene:

Please see my recent paper on postural stability of biped

robots (the concepts are quite relevant to the human). You

can download the paper from:

http://www.cis.upenn.edu/~goswami/papers/paper.html

The paper is:

Postural stability of biped robots and the foot rotation

indicator (FRI) point

A. Goswami

International Journal of Robotics Research, Vol. 18, No. 6, 1999.

If you have any question, I will be happy to answer. My work

in this area continues.

Ambarish Goswami

************************************************** *******************

>So my problem is the following:

>

>"How can one quantify balance? Obviously, the area of the base of support

>and the position of the centre of gravity in relation to it is a

>fundamental concept. But how can this be quantified? Also what about the

>types of base of support and their stability in relation to perturbations

>from various angles?

>From an instrumental approach, we have looked at several ways to assess

balance and postural sway. We have used three methods; force plate,

accellerometers, and motion analysis.

Motion analysis turned out to be the least sensitive of the three.

Force plates are the most conventional method of balance. A force plate is

a large plate (aluminum), that has force sensors in the four corners. The

subject stands in the center of the force plate, and any change in balance

(sway) is picked up by the sensors. When the subject is in balance (no

sway), the forces on the sensors will be equal (or will have reached a

static steady state).

Another way to measure balance is by attaching accelerometers to either the

subjects head or in the region of the C7 vertibra. The accelerometer picks

up motions of the head as the subject tries to maintain an upright

position. I've got some pictures on my web page at

http://www.ecn.ou.edu/~major/www/accel.html .

With either the force plate or the accelerometer method, one can easily

reduce the data (say for a 10 second trial) to a single number. There are

a number of statistical methods to do this, but the easiest (for us) was to

calculate the RMS (root-mean-squared) value for the entire 10 second trial.

The voltage produced by the accelerometer (or force platform) was recorded

via a digital-to-analog board every 1/100 of a second, and stored on the

hard drive as an ascii file (10,000 entries for a 10 second trial).

To calculate the RMS number, the values in the ascii file were all squared.

These numbers were all added up and divided by 10,000 (to calculate the

mean), and the square-root of this number was taken. This gives a single

number corresponding to the total amount of postural sway for the interval

of the trial.

Trying to condense everything down to a single e-mail message, I may have

overlooked or not explained something very well. If you have any

questions, please feel free to post back and I will do my best to help out.

Dan Major

Univ. of Okla. School of Industrial Engineering

major@ou.edu htp://www.ecn.ou.edu/~major

************************************************** ***********************

---------------------------------------------------------------

To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl

For information and archives: http://isb.ri.ccf.org/biomch-l

---------------------------------------------------------------