mecanica alergarii

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Titolo

BIOMECHANICS

OF HUMAN MOVEMENT

Rita Stagni, Silvia Fantozzi, Angelo Cappello

Biomedical Engineering Unit, DEIS,

University of Bologna

Aurelio CappozzoDepartment of Human Movement and Sport Sciences

IUSM, Rome

SUMMER SCHOOL 2006 Monte S.Pietro, Bologna

ADVANCED TECHNOLOGIES FOR NEURO-MOTOR ASSESSMENT AND REHABILITATION

Biomechanics, kinematics, kinetics

Biomechanics is the science concerned with the internaland external forces acting on the human body and theeffects produced by these forces.

Kinematics is the branch of biomechanics concernedwith the study of movement from a geometrical point ofview.

Kinetics is the branch of biomechanics concerned withwhat causes a body to move the way it does.


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Anthropometric parameters

Segmental kinematics (stereophotogrammetry, wearable sensors, etc)

External forces and moments (dynamometry, baropodometry, etc)

Muscular electrical activity (electromyography)

Metabolic energy (indirect calorimetry)

Some variables and parameters can be measured

DiSMUSDiSMUSDiSMUSDiSMUS

BTS

BTS

BTSBTS

BTSBTSBTSBTS

BTSBTSBTSBTS

BTS

BTS

BTS

BTS

BTSBTSBTSBTS

BTSBTSBTSBTS

Gait Analysis Laboratory

BTS

ELITEplus

STEREOPHOTOGRAMMETRIC

SYSTEM

KISTLER

PLATFORM

AMPLIFIER

TELEMG

DYNAMIC

ELECTROMYOGRAPHY

SYSTEM

BTS

DIGIVEC

VHS

VHS AND DIGITAL

RECORDING

SYSTEM

Cameras & Infra-red Strobes

Videocamera

DynamometricPlatforms

LTM


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Instantaneous bone pose(virtual representation of the skeletal system in motion)

Relative movement between adjacent bones(joint kinematics)

Forces transmitted by muscles-tendons-ligaments-bones(joint kinetics)

Muscular mechanical work/powersystem energy variation

(joint energetics)

1

The estimable quantities

4

3

2


In order to describe the pose of the bone as a rigid body

we assume a local reference frame such that the local coordinates

of the bone points are time invariant

Yg

XgZg

yl

xl

zlDiSMUSDiSMUSDiSMUSDiSMUS

INSTANTANEOUS 3D BONE POSE


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Yg

XgZg

The problem is now the mathematical description of the position and orientationof the local reference frame with respect to the global one

The description of the pose

yl

xl

zl


Numerical description of the pose vs time (3-D case)

orientation vector

[ ] kjlzj

g

lyj

g

lxj

g

lj

g ,...,1; ==

[ ] kjtttlzj

g

lyj

g

lxj

g

lj

g ,...,1; ==t

position vector

Six scalar quantitiesin each sampled instant of time

yl

xl

zl

Yg

XgZg

Oll

gtl

g

orientation matrix

kjlj

g ,...,1 =RDiSMUSDiSMUSDiSMUSDiSMUS


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The orientation matrix of the local frame with respect tothe global one is defined by:

1st column xl axis versor components

2nd column yl axis versor components

3rd column zl axis versor components

These components are the cosines of the angles betweeneach versor and the XYZ global axes.

JOINT KINEMATICS


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y

x

z

Sagittal plane

Frontal (coronal)

plane

Transverse plane

Anatomical planes and axes

AP axis

ML axis

V axis


Hip flexion-extension

Flexion (+) Extension (-)

a a



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Knee flexion-extension

Flexion (-) Extension (+)

a g


Ankle dorsal and plantar flexion

Dorsal flexion (+)

Plantar flexion (-)

c

c

Neutral position



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h

a

k

H

K

A

M

A lower limb model

Joint centres:

H Hip

K Knee

A Ankle

M Metatarsus-phalanx V toe

Hypotheses: Planar motion (sagittal plane) Joints are modelled using

cylindrical hinges (1 dof)


Yg

Xg

H

K

A

M

Experimental protocol

Joint centres:

H greater trochanter

K lateral femoral epicondyle

A lateral malleolus

M metatarsus-phalanx V toeDiSMUSDiSMUSDiSMUSDiSMUS


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Yg

Xg

Flexion-extension angles of the lower limb joints during walking

k

a

hip

knee

ankle

0 50 100

[% cycle]

40

-20

90

30

0

-60

[deg]

h

H

K

A

MDiSMUSDiSMUSDiSMUSDiSMUS

Motor task classification


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1) starts from the knowledge, in each sampled instant of time, of the

pose of the bony segments involved in the laboratory frame

2) entails the estimation of the instantaneous pose (position andorientation) of one bony segment relative to the other.

The description of 3-D joint kinematics

yg

zg xg DiSMUSDiSMUSDiSMUSDiSMUS

Motion capture provides these data

yg

xg

zg

orientation vector

[ ] kjczj

g

cyj

g

cxj

g

cj

g ,...,1; ==

kjtttczj

g

cyj

g

cxj

g

cj

g,...,1; ==t

position vector

[ ] kjcippp zijg

yijg

xijg

ijg ,...,;,...,; 11 ===p

position vectors

xczc

yc

xczc

yc

xc

zc

yc

mathematicaloperator


kjcj

g,...,1; =R

orientation matrix


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Relative pose

global orientation matrix

cpgR

Femur

global position vectorycp

xcp

zcp

ycd

xcd

zcd

global orientation matrix

cdgR

Tibia

global position vector

relative position vector&

relative orientation matrix

In any given instant of time:

proximal frame

distal frame

[ ]PzgPygPxgPg ttt=t [ ]DzgDygDxgDg ttt=t

P

D


Relative position

Femur


Tibia


relative position vector in the proximal frame


cp

gR

+

( ) ( ) Pg

cp

g

D

g

cp

g

PD

cp

Pg

gcp

Dg

gcp

PDcp

Pg

Dg

PDg

tRtRt

tRtRt

ttt

TT=

=

=

[ ]PzgPygPxgPg ttt=t [ ]DzgDygDxgDg ttt=tycp

xcp

zcp

ycd

xcd

zcd

PDgt

P

D



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Relative orientation

Femur

global position matrix

Tibia

global position matrix

( ) cdgT

cpg

cdcp RRR =

relative orientation vector in the proximal frame


cp

gRcd

gRycp

xcp

zcp

ycd

xcd

zcd


The two systems of reference are assumed to be aligned,

In summary

then the distal system of reference moves in its new position,

yd

xd

zd

and then it rotates in its new orientation

yp

xpzp

yd

xd

zdDiSMUSDiSMUSDiSMUSDiSMUS


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At the time t1

In summary

at the time t2

yd

xd

zd

yp

xpzp

yd

xd

zd

and so forth

yd

xd

zd

yd

xd

zd

yd

xd

zd

t2t1


Motion is described as the ensemble of

the positions and orientations of the distal

bone with respect to the proximal bone

determined in sampled instants of time

during the observation interval

This matrix, and the three independent scalar quantities embedded in it,completely describe the orientation of the

distal relative to the proximal bone.

orientation matrix of the distal relative to the proximal cluster frame

Orientation

=

pdpdpd

pdpdpd

pdpdpd

zzzyzx

yzyyyx

xzxyxx

cdcp

coscoscos

coscoscos

coscoscos

R

yd

xd

zd

yp

xpzp

cdcpR

However, the relevant scalar components have no physical meaning and, assuch, do not convey readable information about joint rotation. DiSMUSDiSMUSDiSMUSDiSMUS


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Orientation

[ ]cdzcp

cdy

cp

cdx

cp

cd

cp

cd

cp

cd

cp == n

orientation vector of the distal relative to the proximal cluster frame

This vector, and the three independent scalar quantities embedded in it,completely describe the orientation of thedistal relative to the proximal bone.

However, the relevant scalar components have no physical meaning as such.

yd

xd

zd

yp

xpzp

cdcp


n

rotationvirtuala

representsand

rotation,ofaxisvirtuala

representsvectorThecd

cp

cd

cp

n

Problem

Relative position and orientation descriptions illustrated so far carry

all the necessary information relative to joint kinematics,

but

have no direct use in movement analysis



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Orientation

The orientation of the distal relative to the proximal cluster frame

may be described using

a sequence of three rotations about selected axes (Euler Angles).

These rotations have a physical meaning,

Nevertheless, still represent an abstraction !


yp

xpzp

yd

zd

xd

Example: hip joint

pelvis frame

femur frame



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yp

xp

yd

zdzpx

d

zp

yp

xp

yd

zd

xd

Starting orientation Orientation at time t

Example: hip joint


yp

xp

yd1

zd1 zpxd1

Rotation about the axis zd1: femur or pelvis medio-lateral axis

First rotation: flexion-extension



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yp

xp

yd1

zd1

zp

zd2

yd2

xd2 xd1

Rotation about the axis xd2: femur antero-posterior axis

Second rotation: abduction-adduction


yd3 yd2

xd3xd2

yp

xp

zd2zp

zd3

Rotation about the axis yd2: femur longitudinal axis

Second rotation: internal-external rotation



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The three angles of the rotation sequence

depend on both

In summary

,,

the axes about which the rotations are made to occur

the relevant sequence

A generic orientation of a distal relative to a proximal frame

may be obtained as a result of three successive and ordered rotations

about two or three different axes (belonging to either frames).


The Cardan convention

The rotation sequence illustrated previously provides angles that are often

referred to as Cardan Angles*

Grood ES, Suntay WJ. A joint co-ordinate system for the clinical description of three-dimensional motions:application to the knee. Transactions of ASME Biomechanical Engineering1983



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ADDUCTION (-)

ABDUCTION (+)

INT. ROTATION (+)EXT. ROTATION (-)

EXTENSION (-)

FLEXION (+)

JOINT ANGLES

(Grood and Suntay, ASME J.Bionech. 1983)

A question

What happens if the rotation sequence is changed?

Given an orientation of the distal relative to the proximal frame,

60.060.560.460.958.560.5

5.010.011.24.921.711.2

10.01.30.610.019.40.6

zxyyzxxyzzyxxyzyxz[deg]

zp

yp

xp

ydzd

xddepending on the sequence selected the following descriptions are obtained:



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The orientation vector convention

[ ]cdz?cdy?cdx?cdcpcdcpcdcp == n

orientation vector of the distal relative to the proximal frame

yd

xd

zd

yp

xpzp

cdcp

The problem is: in what system of reference should this vector be represented?

The options are:

either the proximal or the distal frame

the joint axes as defined by the Cardan convention

Do not forget: it is a totally abstract representation !

Woltring HJ. 3-D attitude representation of human joints: A standardization proposal. Journal of Biomechanics1994


Sensitivity of the knee joint kinematics to the angular convention

1 - Cardan convention

2 - Orientation vectorprojection on theproximal axes

3 - Orientation vector

projection on theCardan (joint) axes



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position vectoryd

xd

zd

yp

xpzp

Position

PDt?

[ ]???? PDzPDyPDxPD ttt=t

The position vector is represented relative to two points (rigid with theproximal and distal bone, respectively, and

a set of axes of choice

P

DThe selected points may bethe origins of the framesinvolved


The position vector is represented relative to two points (rigid with theproximal and distal bone, respectively) and

a set of axes of choice

yd

xd

zd

yp

xpzp

Position

thus the three scalar quantities that represent positiondepend on the choice of the two reference points and the set of axes.

PDt?

P

D

position vector

[ ]???? PDzPDyPDxPD ttt=t

The selected points may bethe origins of the framesinvolvedor two points arbitrarilyidentified



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c displacement along the distal z axis (coinciding with the proximal z axis)

a displacement along the distal x axis (after the first rotation)

b displacement along the distal y axis (after the second)

The axes with respect to which we represent

the position vector

yd

xdzd

yp

xpzp

PDt?

P

D

yd2

xd1

zdzp a

b

c

An option is represented by the joint axes:


The points with respect to which we represent

the position vector

Example with reference to the knee joint:

P

D

A point (P) in the

proximal set of axes

A point (D) in the

distal set of axes

P and D coincide while the subject assumes an orthostatic posture



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The six degrees of freedom of a joint according to the Cardan convention

about the distal z axis (coinciding with the proximal z axis)

about the distal x axis (after the first rotation) about the distal y axis (after the second rotation)c displacement along the distal z axis (coinciding with the proximal z axis)

a displacement along the distal x axis (after the first rotation)

b displacement along the distal y axis (after the second)

yd2

xd1

zdzp

cb

a

In summaryDiSMUSDiSMUSDiSMUSDiSMUS

A set of orthogonal axes rigid with the proximal bone (p)

A set of orthogonal axes rigid with the distal bone (d)

A point (P) in the proximal set of axes

A point (D) in the distal set of axes

The three axes with respect to which the position vector of the distal

bone relative to the proximal bone is represented

The axis about which the first rotation is performed

The axis about which the second rotation is performed

The axis about which the third rotation is performed

In summary

In order to determine the six quantities that describe the position and

orientation of the distal bone relative to the proximal bone the following

entities must be defined:



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Knee joint kinematics vs orientation of the proximal axes

proximal frame rotatedabout the y axis of 5

proximal frame rotatedabout the x axis of 5

nominal referencesystems


The representation of jointkinematics, whateverconvention is chosen, isvery sensitive to thedefinition of the set of axesinvolved

The two requirements are met by using anatomical frames

These sets of axes are repeatable

because they rely on identifiable anatomical landmarks

They are anatomical axes and define anatomical planes: thus,

the joint six degrees of freedom may be named in a manner

consistent with functional anatomy


The definition of anatomical frames is not unique

Possible definitions are


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Conventional Gait Model (Plug-in-Gait di VICON) 1

Calibrated Anatomical System Technique (CAST)2

ISB recommendation3

Pelvis

1 Davis III RB, Ounpuu S, Tyburski D, Gage JR. A gait analysis data collection and reduction technique.Human

Movement Sciences, 19912Cappozzo A, Catani F, Croce UD, Leardini A. Position and orientation in space of bones during movement:

Anatomical frame dedinition and determination.Clinical Biomechanics 19953Wu G, Cavanagh PR. ISB recommendations for standardization in the reporting of kinematic data.Journal of

Biomechanics1995


Centre of head of the femur

Femur

TF

Conventional Gait ModelCAST

ISB recommendation



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Femur

Mid-point between the femur epicondyles

ELEM

Conventional Gait Model

CASTISB recommendation


Femur

Conventional Gait ModelCAST

ISB recommendation



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JOINT KINETICS

Example: internal loads

acting at the knee


The problem: musculo-skeletal loading


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Loads transmitted by relevant tissues

http://www.rad.upenn.edu/rundle/Knee/kneeMRICONT.htmlDiSMUSDiSMUSDiSMUSDiSMUS

Semimembranosus Muscle

Gastrocnemius, Medial Head

Biceps Femoris

Gastrocnemius, Lateral Head

Sartorius Muscle

Plantaris

Medial Collateral Ligament

Posterior Cruciate Ligament

Patellar tendon

http://www.rad.upenn.edu/rundle/Knee/kneeMRICONT.html




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Gastrocnemius, Medial HeadGastrocnemius, Lateral Head

Patellar tendon




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Patellar tendon



Gastrocnemius, Medial HeadGastrocnemius, Lateral Head


Bone-to-bone

Patellar tendon




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Forces transmitted by muscles


QFh

Fg

Fp

Q centroid of the cross sectional area


distributed forces are assumed to be parallel and uniform



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Patellar tendon

Semimembranosus MuscleBone-to-bone Fh

FgFp


Forces exchanged between bones




Patellar tendon


FgFp



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Forces exchanged between bones: resultant force and couple




Patellar tendon


FgFp

Q

Fb






Patellar tendon


FgFp

Q

Fb

X

assumption



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Q

Forces exchanged between bones: resultant force

?




K

Q

LE

ME

Forces exchanged between bones: resultant force




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Patellar tendon


FgFp

K

Fb

Cb

Q


Internal load modelling



Patellar tendon

Semimembranosus MuscleBone-to-bone

Fh

FgFp

K

Fb

Cb



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Muscles, tendons and ligaments are treated as if they were ropes!

no 3-D modelling

no interaction with surrounding muscles and bony structuresis taken into consideration

Continuum mechanics (FEM) and a 3-D approach should be used

Internal load modellingDiSMUSDiSMUSDiSMUSDiSMUS

Construction of the free-body diagram

of the shank and foot system



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=+++++++=+++++

ICCMMMMMMamFFFFWR

KRb

K

F

K

F

K

F

K

F

K

W

K

R

CMbpgh

bpgh

Fh

Fp

FgFb

Cb

W

CR

R

The equations of motion (limited to plane motion)

K


Intersegmental force and couple: definition

W

CR

R

Fis

Cis

K

b

K

F

K

F

K

F

K

Fis

bpghis

CMMMMC

FFFFF

bpgh++++=

+++=

for the time being the point K is chosen arbitrarily

Fh

Fp

FgFb

Cb

W

CR

R



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inertia parameters

Intersegmental force and couple: estimation (limited to plane motion)

kinematic quantities

reaction forcesW

CR

R

Fis

Cis

K

=++++

=++

ICCMMM

amFWR

KRisKF

KW

KR

CMis

is


Kinematic quantities

position vector and orientation matrix ,relative to the

laboratory (g) frame, of the anatomical frame (a), in

each sampled instant of time

local position vector of the intersegmental loads

reduction point K

For each body segment of interest, the following quantities are estimated:

Kap

ag

ag , Rt



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Kinematic quantities & inertia parameters

position vector and orientation matrix ,relative to the

laboratory (g) frame, of the anatomical frame (a), in

each sampled instant of time

local position vector of the intersegmental loads

reduction point K

mass

local position vector of the CM

principal axes of inertia (i) orientation matrix relative

to the anatomical frame (a)

moments of inertia

m

ia

zyx ,I,II

CM

ap

For each body segment of interest, the following quantities are estimated:

ag

ag , Rt

Kap


W

CR

R

Fis

Cis

K

Intersegmental force and couple: estimate

=++++

=++

ICCMMM

amFWR

KRis

K

F

K

W

K

R

CMis

is



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CR

R

Forces exchanged between foot and floor

(ground reactions)


Forces exchanged between foot and floor

(ground reactions)



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Foot-ground contact area during level walking

BIOM-Essen/HennigDiSMUSDiSMUSDiSMUSDiSMUS

Forces acting on the force plate

distributed forces force-couple system

in a given instant of time

C

F

Y

X

ZO



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The force plate supplies six scalar quantities

O

Y

X

Z

O

Fx Fy Fz Cx Cy Cz

F

C


Reaction force and couple

For each body segment interacting with the environment, the followingquantities are estimated:

three force components three couple components.

These quantities are given with respect to the dynamometer frame. Since,normally, the kinematic quantities are given with respect to another set of

axes (referred to as the laboratory axes), the transformation matrix betweenthe former and the latter set is to be provided.

Y

ZX



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Intersegmental force and couple: estimate

W

CR

R

Fis

Cis

K

?inverse dynamics

How accurately do we estimate the intersegmental force and couple?

Do intersegmental loads carry functional information?

is

is

C

F

=++++

=++

ICCMMM

amFWR

KRisKF

KW

KR

CMis

is


Intersegmental force and couple: accuracy factors

The physical model (degrees of freedom)

Inertia parameter estimate

Time differentiation

External forces

Position and orientation reconstruction of the model links

External and internal anatomical landmarks identification



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R

CR

R

CR

estimated measured

open kinematic chain 2-D model 3 dof

Intersegmental force and couple: accuracy

Model (includes input data errors) fidelity assessment

Herbert Hatze, Journal of Biomechanics, 2002



estimated using photogrammetric data (inverse dynamics)measured

average rms difference = 17% of peak-to-peak valueaverage correlation coefficient = 0.87

M-L COUPLE (Nm)A-P FORCE (N) VERTICAL FORCE (N)

850

-200

-150

-100

-50

050

100

0 100

% of task duration-50

0

50

0 100

% of task duration650

700

750

800

0 100

% of task duration



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RCR

O


Redundancy may be exploited for finetuning the parameters and variablesinvolved.

In the bottom-up approach a possiblecriterium is to minimize the trunkresidual moment and force.


Position and orientation reconstruction of the model links

photogrammetric errors soft tissue artefacts anatomical landmark identification



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Shank soft tissue artefacts: effect on knee intersegmental couple

Manal et al., Gait and Posture, 2002

% of stance

Flexion/extension Adduction/abduction Internal/external rot.

Intersegmental couple [Nm]


minimization of skin movement artefacts and/or theirassessment and compensation

minimization of misidentification of both internal andexternal anatomical landmarks

identification of the bone-to-bone resultant forceapplication line

standardization of procedures

muscle, tendon, and ligament modelling

Problems still seeking for an optimal solution



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Do intersegmental loads carry functional information?

W

CR

R

Fis

Cis

K

all vectors are represented in the global (inertial frame)

=++++

=++

ICCMMM

amFWR

KRisKF

KW

KR

CMis

is


The intersegmental couple

point K was chosen arbitrarily !

bKF

KF

KF

KFis CMMMMC bpgh ++++=

Fh

Fp

FgFb

Cb

W

CR

RK

W

CR

R

Fis

Cis

K



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Patellar tendon


FgFp

Q

Fb

X

assumption


The muscular moment

there exists a point Q for which 0CM bQ

Fb=+

thus:

In this case we may refer to the intersegmental couple as muscular moment

W

CR

R

Fis

Cis

K

Fh

Fp

FgFb

Cb

W

CR

RK

QF

QF

QFis pgh

MMMC ++=

bKF

KF

KF

KFis CMMMMC bpgh ++++=



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The challenge

is to find the point Q for which it is true that

and thus:

NIH

Q

Q

F

Q

F

Q

Fis pghMMMC ++=

0CM bQFb

=+


If the knee joint is modelled using a spherical hinge

0C b = 0MQFb=

Fh

Fp

FgFb

Cb

W

CR

R

Fh

Fp

FgFb

Cb

W

CR

R Q

by definition

and, thus, the intersegmental couple is the muscular momentDiSMUSDiSMUSDiSMUSDiSMUS


50/62

The muscular forces

W

CR

R

Fis

Cis

K

This relationship cannot be solved with respect to a single muscular force*unless it is known or assumed that only one muscular force is present

Fh

Fp

FgFb

Cb

W

CR

RK

QF

QF

QFis pgh

MMMC ++=


Gait Analysis


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Gait Phases

INVERSE PENDULUMThe body center of mass rotates

around the support and increases itspotential energy during the initialstance phase: This energy isconverted in kinetic form during thesecond stance phase (Cavagna et al.1977). Il center of mass isaccelerated forward.


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Ground Reaction Forces in Normal Gait

0

0.6

1.2

0 50 100

0.3

0

-0.3

0.1

-0.2

0

% stanceScaled by body weight

Medial/Lateral

Anterior/Posterior

Vertical

Courtesy of National Institutes of Health - USA


Center of Pressure during Normal Gait


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Joint Moments during Normal Gait

HipFlexor (+)

KneeExtensor (+)

AnkleDorsiflexor (+)

0.5

-0.75

-2.00

1.0

0

-1.01.0

0

-1.0

0 25 50 75 100% stance

Nm/kg

Courtesy of National Institutes of Health - USA


Joint Moment Interpretation

Limitations

Cannot distribute moment among each agonist of a musclegroup

Moment does not account for co-contraction (moment =agonist + antagonist effects)

Moment reflects contributions from active (muscular) andpassive (ligament, joint contact) sources

Areas of caution

End range of motion

External devices orthoses, prostheses



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Electromyography

Electromyography

Electromyography (EMG) Study of muscle

function through the examination of the

muscles electric signals

Why EMG?

Estimate in vivo muscle forces for various

activities

Help solving the inverse dynamic problem

Detect muscle fatigue

Quantify pathological muscle behaviour


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History Luigi Galvani 1791

Observed the relationship between muscle and electricity

by depolarizing frog legs with metal rods

Father of neurophysiology

De Viribus Electricitatis work was introduced

Carlo Matteucci 1838

Proved that electric currents originated in muscles

Du Bois-Reymond 1849 Designed a Galvanometer to record electrical current

Reduced skin impedance by rubbing blisters on his arms

and opening them

Galvani

De Luca 1985


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EMG types

Surface EMG (SEMG) Electrodes areapplied to the surface of the skin.

Used to measure muscle signals in largemuscles that lie close to the surface of the skin

Indwelling EMG Electrodes are insertedinto the muscle (usually via a needle)

Used to measure muscle signals in small ordeep muscles, which cannot be adequatelymonitored using SEMG.

EMG Characteristics

Ranges from 0-10mV (peak to peak)

Usable frequency range: 0-500Hz

Dominant frequencies 50-150Hz

Random in nature

Mixture of signals from different motor units


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Action Potentials

De Luca 1982

Surface or Indwelling EMG

Electrodes

Single electrode with reference

Measure action potential at one electrode

Subtract common as measured from reference

Two electrodes with reference

Measure action potentials at both electrodes

Use differential amplifier

Subtract common signal at source

Amplify differences


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Noise

EMG signals are very small

External noise

Electronics noise

Recording/measuring equipment

Ambient noise

TV, radio, overhead lights Motion artifact

Movement of electrodes or wires

Electrode Placement

Place electrodes In line with muscle fibers

At the midline of the muscle

Not over or near tendon insertion sites or innervation zone(motor point) Electrical stimulation at this point results in muscle contraction

Action potentials move oddly and EMG detection is affected

Reference electrode is far away and over electrically neutralarea


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Electrode Placement

De Luca

De Luca

Effects of

Muscle Fatigueon EMG Signal


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Experimental Example

Agonist and Antagonist Muscle

Activity

De Luca 1985


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Data Acquisition and Analysis Sampling

1024 Hz, 12 bit resolution

Bandpass 1st order filter: 10-500Hz

Filter Data

Full wave rectified

4th order Butterworth filter: Fc = 3Hz (smooth)

Further analysis options

Integrated over specific time periods for iEMG

EMG Limitations

Difficult to compare between subjects

SEMG is not appropriate for all muscles

Electrode positioning must be consistent

MVC can vary between days and time of day Cant ensure that all motor units are firing for MVC

Difficult to hold isometric contractions for some muscles

Force is not proportional to EMG amplitude for many muscles

MUST CALIBRATE AT START OF SESSION


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SUMMER SCHOOL 2006 Monte S.Pietro, Bologna

ADVANCED TECHNOLOGIES FOR NEURO-MOTOR ASSESSMENT AND REHABILITATION

mecanica alergarii

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