kirtley24

02-27-2007, 12:55 AM

G'day everyone from Vientiane, People's Democratic Republic of Laos (he

says, just to get Laos into BIOMCH-L for the first time...).

I would like to take the opportunity to ask a question one of my students

once raised. When we calcuate/estimate joint moment, we model the

muscle-tendon-joint system as a "torque motor", implying a free-spinning

spindle driven by a rotation torque. I wonder what the assumptions aee

behind this model - e.g. does it necessarily assume that the tendon moment

arm is small?

I ask because this student showed me a very complex analysis (beyond my ken)

showing that the torque-motor assumption broke down when the tendon moment

arm >> 0.

Chris

On 2/24/07, David Smith wrote:

>

> Dear Sae Yong Lee

>

> I can see why you can get confused with all the terminology and many

> papers

> don't state whether they are presenting external or internal moments and

> in

> what terms.

> I will assume you are working in a 2D frame.

>

> This is my explanation:

>

> 1) Moments are the result of a minimum of two opposing offset forces that

> have lever arm about a point of interest acting on a body, known as

> a force

> couple, and cause a tendency for that body to rotate. (This would be a lot

> easier if we could post diagrams) So usually in the human body the applied

> forces cause rotation at the joints. This as a result of the force couple

> between Joint force (bone and soft tissue) and internal or external forces

> E.G. muscle or GRF.

>

> So a moment is (Force * lever arm) but only if there is an equal and

> opposite (force * lever arm) (lever arm also known as moment arm)

>

> It seems simple but is very useful to remember that all forces are equal

> and

> opposite and the sum of all forces is zero and this is is true for

> moments.

> F-m*a=0 applied forces or moments - resisting forces or moments = 0 The

> forces and moments in any mechanical system, dynamic or static, are always

> in eqilibrium.

> Therefore when speaking of the magnitude of forces and moments it is

> necessary to define when we mean applied or resisting since the sum of the

> two is always zero and the product of each are always equal..

>

> Terminology:

> Applied force: That force acting on the body of interest

> Resisting force: That force resisting the applied force

>

> External force: In terms of biomechanics is usually the force applied by

> GRF

> or some force extrinsic to or outside the body EG the weight of a kettle

> held in a hand or the force of a boxing glove applied against a boxers

> head.

> This can also be thought of as an external moment.

> Internal force: Is usually the force that resists the external force and

> is

> exerted by forces intrinsic or inside the body EG muscles, inertia,

> ligaments, bone.

> This could also be thought of as an internal moment.

>

> Clockwise moment: Is a way of defining the rotation or tendency to rotate

> of the moment (force * lever arm) in a 2D plane.

> Anticlockwise moment: (Anticlockwise and clockwise moments can also be

> thought of as positive and negative moments as can the forces but stick

> with

> the former for now)

>

> You may be able to see from the above descriptions that a moment in a

> given

> direction (say anticlockwise) about a joint of interest may be the sum of

> external and internal forces.This may be where you get confused since

> External forces * lever arm + Internal forces * lever arm = internal and

> external moments acting in the same direction, when intuitively you might

> imagine they would be in opposite direction.

>

> The easiest way to imagine and summate the moments is to find all the

> forces

> * lever arms causing an anticlockwise rotation minus the forces * lever

> arms causing a clockwise rotation about the joint of interest. This

> negates

> (cancells the importance of) the fact of whether they are internal or

> external. Can you see that Internal and external are not absolute terms

> but

> more a comparative term. So therefore in terms of the body as a whole a

> given force or moment of interest may be internal or intrinsic but in

> terms

> of a given joint of interest the same force or moment may be external or

> extrinsic to that joint.

>

> Nett: That sum remaining after all deductions from the gross or grand

> total.

> Gross sum: = total sum of everything

> Nett sum: = the gross sum less a certain individual sum of interest.

> Therefore it could be said that the individual sum is the nett sum. EG

> Gross

> of all stock value of a shop = £117.50 - Gross sum net of Value Added Tax

> at

> 17.5% = £100 - Nett sum of VAT = £17.50

>

> Joint moment: is the sum of moments acting about the joint of interest,

> which is ZERO. The NET sum of joint anticlockwise moments = X and the NET

> sum of joint clockwise moments = Y (X - Y = 0)

>

> 2) So you may now see that although all moments within the mechanical

> system must be in equilibrium we cannot easily directly measure the

> internal

> moments and forces of the muscles and joints and bones etc. We can however

> measure the external forces (external and internal in terms of the whole

> body) of GRF for instance.

> Then by using the laws of Newton to caculate the external moments about a

> joint of interest we can, by knowing that moments are equal and opposite,

> calculate the forces required from the internal structures for equlibrium

> of

> moments to be established. This is known as inverse dynamics using linked

> segment models. It is inverse because the action is reversed whereas in

> real

> life (some would say) muscles are the initiating or driving force and not

> GRF for instance. (For me the two are inseperable as the muscles could not

> move the body without the opposite action of external forces).

>

> 3) There are two basic systems for studying Human movement, a) Kinetics

> =forces and b) Kinematics = motion, Vicon or Motion monitor systems

> characterise the kinematics (motion) of the joint and limb. Therefore they

> do not measure related forces, which are Kinetics, which can be measured

> using a force plate for instance, moments can then be calculated. It is

> possible to calculate the forces and moments from the kinematics by

> finding

> the product of the accelerations of a limb and its body parameters. This

> is

> known as the Forward solution or Forward Dynamics.

> This brings the Anthropometry into the picture and Anthropometry is the

> knowledge of the body parameters such as Dimensions, Mass, CoM and Radius

> of

> Gyration of a segment and the location of its joint centres. These are

> necessary for both forward and inverse dynamic calculations.

> A good reference for this is Biomechanics and Motor Control of Human

> Movement, David Winter, Wiley interscience NY.isbn 0-471-50908-6

>

> Does this help? all the best Dave Smith.

>

>

>

>

> ----- Original Message -----

> From: "Sae Yong Lee"

> To:

> Sent: Friday, February 23, 2007 4:07 PM

> Subject: [BIOMCH-L] about definition of moment

>

>

> > Dear Biomch-L subscriber

> >

> > My name is Sae Yong Lee. I am doctorate student studying at University

> of

> > Virginia in Kinesiology program.

> > I have question related to moment. Are there anyone help me to clarify

> the

> > definition of moment related termiology?

> > 1. Difference between joint moment, net joint moment, external moment,

> > muscle moment, and internal moment. I'll write down my understanding of

> > those terms.

> > Joint moment: The moment acting at the joint to overcome external

> moment.

> > net joint moment: Sum of all moment acting at the joint including

> internal

> > (active (muscle) + passive (ligament, joint capsule...), external

> moment.

> > muscle moment: Moment produced by the muscle (different to quantify

> using

> > motion analysis system).

> > Internal moment: Moment produced by active (muscle) + passive (ligament,

> > joint capsule...). part of joint moment.

> > external moment: Moment produced by external forces such as ground

> > reaction force.

> > Please give me some comments whether or not my understanding is right.

> >

> > 2. What is general Newtonian inverse dynamics calculating? I have been

> > believed that it is internal moment which is moment produced by passive

> > and active structures crossing the joint. But I got confused these days

> > while I was reading articles. It seems like quite a lot of articles

> > alternatively use all those terms I mentioned. Even though the several

> > articles use same system to calculate Moment, one said it is external

> > moment and the other said internal moment. Is it joint moment, net joint

> > moment, external moment, muscle moment, or internal moment.

> >

> > 3. If anyone use Vicon system or Motion monitor system, what kind of

> > moment does this system calculating? Are there any reference article

> that

> > mention about the calculation of moment of these systems?

> >

> > Thanks

> >

> > __________________________________________________ _______________

> > FREE pop-up blocking with the new MSN Toolbar - get it now!

> > http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/

> >

> > ---------------------------------------------------------------

> > Information about BIOMCH-L: http://www.Biomch-L.org

> > Archives: http://listserv.surfnet.nl/archives/Biomch-L.html

> > ---------------------------------------------------------------

> >

>

> ---------------------------------------------------------------

> Information about BIOMCH-L: http://www.Biomch-L.org

> Archives: http://listserv.surfnet.nl/archives/Biomch-L.html

> ---------------------------------------------------------------

>

--

Dr. Chris Kirtley MB ChB, PhD

608 Dockside

44 Ferry St.

Kangaroo Point

Queensland 4169

Australia

Tel. (07) 3891 6644 x 1608

Fax 3891 6900

Clinical Gait Analysis: http://www.univie.ac.at/cga

Book:

http://www.amazon.co.uk/exec/obidos/ASIN/0443100098/203-6674734-4427132

says, just to get Laos into BIOMCH-L for the first time...).

I would like to take the opportunity to ask a question one of my students

once raised. When we calcuate/estimate joint moment, we model the

muscle-tendon-joint system as a "torque motor", implying a free-spinning

spindle driven by a rotation torque. I wonder what the assumptions aee

behind this model - e.g. does it necessarily assume that the tendon moment

arm is small?

I ask because this student showed me a very complex analysis (beyond my ken)

showing that the torque-motor assumption broke down when the tendon moment

arm >> 0.

Chris

On 2/24/07, David Smith wrote:

>

> Dear Sae Yong Lee

>

> I can see why you can get confused with all the terminology and many

> papers

> don't state whether they are presenting external or internal moments and

> in

> what terms.

> I will assume you are working in a 2D frame.

>

> This is my explanation:

>

> 1) Moments are the result of a minimum of two opposing offset forces that

> have lever arm about a point of interest acting on a body, known as

> a force

> couple, and cause a tendency for that body to rotate. (This would be a lot

> easier if we could post diagrams) So usually in the human body the applied

> forces cause rotation at the joints. This as a result of the force couple

> between Joint force (bone and soft tissue) and internal or external forces

> E.G. muscle or GRF.

>

> So a moment is (Force * lever arm) but only if there is an equal and

> opposite (force * lever arm) (lever arm also known as moment arm)

>

> It seems simple but is very useful to remember that all forces are equal

> and

> opposite and the sum of all forces is zero and this is is true for

> moments.

> F-m*a=0 applied forces or moments - resisting forces or moments = 0 The

> forces and moments in any mechanical system, dynamic or static, are always

> in eqilibrium.

> Therefore when speaking of the magnitude of forces and moments it is

> necessary to define when we mean applied or resisting since the sum of the

> two is always zero and the product of each are always equal..

>

> Terminology:

> Applied force: That force acting on the body of interest

> Resisting force: That force resisting the applied force

>

> External force: In terms of biomechanics is usually the force applied by

> GRF

> or some force extrinsic to or outside the body EG the weight of a kettle

> held in a hand or the force of a boxing glove applied against a boxers

> head.

> This can also be thought of as an external moment.

> Internal force: Is usually the force that resists the external force and

> is

> exerted by forces intrinsic or inside the body EG muscles, inertia,

> ligaments, bone.

> This could also be thought of as an internal moment.

>

> Clockwise moment: Is a way of defining the rotation or tendency to rotate

> of the moment (force * lever arm) in a 2D plane.

> Anticlockwise moment: (Anticlockwise and clockwise moments can also be

> thought of as positive and negative moments as can the forces but stick

> with

> the former for now)

>

> You may be able to see from the above descriptions that a moment in a

> given

> direction (say anticlockwise) about a joint of interest may be the sum of

> external and internal forces.This may be where you get confused since

> External forces * lever arm + Internal forces * lever arm = internal and

> external moments acting in the same direction, when intuitively you might

> imagine they would be in opposite direction.

>

> The easiest way to imagine and summate the moments is to find all the

> forces

> * lever arms causing an anticlockwise rotation minus the forces * lever

> arms causing a clockwise rotation about the joint of interest. This

> negates

> (cancells the importance of) the fact of whether they are internal or

> external. Can you see that Internal and external are not absolute terms

> but

> more a comparative term. So therefore in terms of the body as a whole a

> given force or moment of interest may be internal or intrinsic but in

> terms

> of a given joint of interest the same force or moment may be external or

> extrinsic to that joint.

>

> Nett: That sum remaining after all deductions from the gross or grand

> total.

> Gross sum: = total sum of everything

> Nett sum: = the gross sum less a certain individual sum of interest.

> Therefore it could be said that the individual sum is the nett sum. EG

> Gross

> of all stock value of a shop = £117.50 - Gross sum net of Value Added Tax

> at

> 17.5% = £100 - Nett sum of VAT = £17.50

>

> Joint moment: is the sum of moments acting about the joint of interest,

> which is ZERO. The NET sum of joint anticlockwise moments = X and the NET

> sum of joint clockwise moments = Y (X - Y = 0)

>

> 2) So you may now see that although all moments within the mechanical

> system must be in equilibrium we cannot easily directly measure the

> internal

> moments and forces of the muscles and joints and bones etc. We can however

> measure the external forces (external and internal in terms of the whole

> body) of GRF for instance.

> Then by using the laws of Newton to caculate the external moments about a

> joint of interest we can, by knowing that moments are equal and opposite,

> calculate the forces required from the internal structures for equlibrium

> of

> moments to be established. This is known as inverse dynamics using linked

> segment models. It is inverse because the action is reversed whereas in

> real

> life (some would say) muscles are the initiating or driving force and not

> GRF for instance. (For me the two are inseperable as the muscles could not

> move the body without the opposite action of external forces).

>

> 3) There are two basic systems for studying Human movement, a) Kinetics

> =forces and b) Kinematics = motion, Vicon or Motion monitor systems

> characterise the kinematics (motion) of the joint and limb. Therefore they

> do not measure related forces, which are Kinetics, which can be measured

> using a force plate for instance, moments can then be calculated. It is

> possible to calculate the forces and moments from the kinematics by

> finding

> the product of the accelerations of a limb and its body parameters. This

> is

> known as the Forward solution or Forward Dynamics.

> This brings the Anthropometry into the picture and Anthropometry is the

> knowledge of the body parameters such as Dimensions, Mass, CoM and Radius

> of

> Gyration of a segment and the location of its joint centres. These are

> necessary for both forward and inverse dynamic calculations.

> A good reference for this is Biomechanics and Motor Control of Human

> Movement, David Winter, Wiley interscience NY.isbn 0-471-50908-6

>

> Does this help? all the best Dave Smith.

>

>

>

>

> ----- Original Message -----

> From: "Sae Yong Lee"

> To:

> Sent: Friday, February 23, 2007 4:07 PM

> Subject: [BIOMCH-L] about definition of moment

>

>

> > Dear Biomch-L subscriber

> >

> > My name is Sae Yong Lee. I am doctorate student studying at University

> of

> > Virginia in Kinesiology program.

> > I have question related to moment. Are there anyone help me to clarify

> the

> > definition of moment related termiology?

> > 1. Difference between joint moment, net joint moment, external moment,

> > muscle moment, and internal moment. I'll write down my understanding of

> > those terms.

> > Joint moment: The moment acting at the joint to overcome external

> moment.

> > net joint moment: Sum of all moment acting at the joint including

> internal

> > (active (muscle) + passive (ligament, joint capsule...), external

> moment.

> > muscle moment: Moment produced by the muscle (different to quantify

> using

> > motion analysis system).

> > Internal moment: Moment produced by active (muscle) + passive (ligament,

> > joint capsule...). part of joint moment.

> > external moment: Moment produced by external forces such as ground

> > reaction force.

> > Please give me some comments whether or not my understanding is right.

> >

> > 2. What is general Newtonian inverse dynamics calculating? I have been

> > believed that it is internal moment which is moment produced by passive

> > and active structures crossing the joint. But I got confused these days

> > while I was reading articles. It seems like quite a lot of articles

> > alternatively use all those terms I mentioned. Even though the several

> > articles use same system to calculate Moment, one said it is external

> > moment and the other said internal moment. Is it joint moment, net joint

> > moment, external moment, muscle moment, or internal moment.

> >

> > 3. If anyone use Vicon system or Motion monitor system, what kind of

> > moment does this system calculating? Are there any reference article

> that

> > mention about the calculation of moment of these systems?

> >

> > Thanks

> >

> > __________________________________________________ _______________

> > FREE pop-up blocking with the new MSN Toolbar - get it now!

> > http://toolbar.msn.click-url.com/go/onm00200415ave/direct/01/

> >

> > ---------------------------------------------------------------

> > Information about BIOMCH-L: http://www.Biomch-L.org

> > Archives: http://listserv.surfnet.nl/archives/Biomch-L.html

> > ---------------------------------------------------------------

> >

>

> ---------------------------------------------------------------

> Information about BIOMCH-L: http://www.Biomch-L.org

> Archives: http://listserv.surfnet.nl/archives/Biomch-L.html

> ---------------------------------------------------------------

>

--

Dr. Chris Kirtley MB ChB, PhD

608 Dockside

44 Ferry St.

Kangaroo Point

Queensland 4169

Australia

Tel. (07) 3891 6644 x 1608

Fax 3891 6900

Clinical Gait Analysis: http://www.univie.ac.at/cga

Book:

http://www.amazon.co.uk/exec/obidos/ASIN/0443100098/203-6674734-4427132