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Mechanics of human movementMechanics of human movement

M. Foidart-Dessalle (Prof. FM, ULg)S. Cescotto (Prof. FSA, ULg)

F. Pascon (FNRS)

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Structures implied in movementStructures implied in movement

Bones and JointsBones and Joints: : Moving StructuresMoving Structures

Motor forcesMotor forces: : Gravity, Gravity, muscle contractionsmuscle contractions, , friction forces, friction forces, ground reaction, aquatic, …. ground reaction, aquatic, ….

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KinematicKinematic conventionsconventions

Kinematics (descriptive analysis)Kinematics (descriptive analysis)displacement, velocity, displacement, velocity, accelerationacceleration

Kinetics (causal analysis)Kinetics (causal analysis)forcesforces

Necessary to analyze human motion

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LES CHAINONS

OSSEUX

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Schematic representation of jointsSchematic representation of joints

Joints (rotation centers) are represented as pointsIt is a necessary approximation Rotation centers are between 18.9 (scapula) and 12 (elbow) square mm

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Schematic model of human bodySchematic model of human body

Segments joining points:mechanical axis# of anatomic axis

Either all body, either part of it: limb, part of it

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KinematicsKinematics

Position = localization in spaceGlobal reference frame neededUse a “human reference frame”Movements wrt the “human reference frame”Relative movements of the limbs

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« Humanreference frame »

3 reference planes

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Examples of movements that could be described wrt the “human reference frame”

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Examples of relative movements between limbs

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Classification of diarthroses withconcordant surface

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KinematicKinematic analysisanalysis: position/: position/timetime

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Numeric and graphic analysisNumeric and graphic analysis

For complex movementsvelocity and acceleration

can be calculated from positioncan be calculated from position--time time data obtained with high precision data obtained with high precision cameras and chronometerscameras and chronometers

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Graphic resolutionGraphic resolution

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Graphic resolutionGraphic resolution

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Historical:Chronophotography – running man

Measurement techniquesMeasurement techniques

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Historical:Chronophotography – walking man

Measurement techniquesMeasurement techniques

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Measurement techniquesMeasurement techniquesHistorical:

Chronophotography

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Measurements techniques Measurements techniques Stroboscopic flashStroboscopic flash

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Measurement techniques Measurement techniques ElectrogoniometryElectrogoniometry

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camera

platform for force measurement

Measurement techniquesMeasurement techniques

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Electrodes inside the muscles for precise measurements of

muscle activity

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hip curve and numerical walk

3D and numerical walk

Electrodes on the muscle for simple measurements of

muscle activity

Reflecting spheres to capture the movement by 5 cameras

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Anthropometric requirementsAnthropometric requirements

Length of the segmentsWeight and density of whole body and segmentsThe center of mass locationMoment of inertia and radius of giration

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Length of segmentsLength of segments

Necessary determination to represent Necessary determination to represent the body and its segments at the right the body and its segments at the right scalescale

Direct measure is preferableDirect measure is preferable

Data from tables give length of segments Data from tables give length of segments as fractions of whole body heightas fractions of whole body height

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Useful in determination of mass centers Useful in determination of mass centers and moments of inertiaand moments of inertia

In the past it was measured on cadavers/ In the past it was measured on cadavers/ then on segments volumes with tables /then on segments volumes with tables /nowadays on crossnowadays on cross--sections obtained by sections obtained by scanning the segments at regular intervalsscanning the segments at regular intervals

Whole body densityWhole body density

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Measurements with tablesDirect measurements with

accelerometers:

quick release experiment

Determination of mass centers Determination of mass centers and moments of inertiaand moments of inertia

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Whole body densityWhole body density

Density of the whole body depends on Density of the whole body depends on respective density of bone (>1.8), muscle respective density of bone (>1.8), muscle ((≤≤1), fat (<1)1), fat (<1)

Ponderous index in metric units Ponderous index in metric units c = c = h/wh/w : kg/m: kg/m

Whole body density Whole body density d = 0.69 + 0.9 cd = 0.69 + 0.9 c

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Segment densitiesSegment densities

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Segments weight ratiosSegments weight ratios

Upper body part / Lower body part: 5/3Upper body part / Lower body part: 5/3Head and trunk / both upper limbs: 4/1Head and trunk / both upper limbs: 4/1Head / trunk: 1/6Head / trunk: 1/6Arm / forearm and hand: 1/1Arm / forearm and hand: 1/1Hand / Forearm: 1/3Hand / Forearm: 1/3Thigh / leg and foot: 5/3Thigh / leg and foot: 5/3Leg / foot: 3/1Leg / foot: 3/1

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Muscles anthropometric dataMuscles anthropometric data

Physiological Cross sectional Area (PCA) of a Physiological Cross sectional Area (PCA) of a muscle is a measure of the numbers of muscle is a measure of the numbers of sarcomerssarcomers(contractile units) parallel to the angle of pull of the (contractile units) parallel to the angle of pull of the muscle. In muscle. In pennatepennate muscles, only the parallel muscles, only the parallel component in effective. component in effective. PCA = m PCA = m coscos θθ / D l / D l θθ = = pennationpennation angle angle m = mass D = density l = lengthm = mass D = density l = lengthForce/unit cross section area ranges from 0.20 to Force/unit cross section area ranges from 0.20 to 1MPa 1MPa (0.70 MPa in quadriceps during running andjumping)

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5 deg25 cm²6.8 cm180 gVastus intermedius

5 deg26 cm²7.2 cm200 gVastus medialis

5 deg30 cm²6.7 cm210 gVastus lateralis

5 deg12.5 cm²6.8 cm90 gRectus femoris

5 deg9.1 cm²7.3 cm70 gTibialis anterior

15 deg21 cm²2.4 cm55 gTibialis posterior

15 deg30 cm²4.8 cm158 gGastrocnemius

30 deg58 cm²3.0 cm215 gSoleus

04.4 cm²16 cm75 gSemitendinosus

015.8 cm²9 cm150 gBiceps femoris

01.9 cm²38 cm75 gSartorius

Pennation anglePCAFiber lengthMassMuscle

5 deg25 cm²6.8 cm180 gVastus intermedius

5 deg26 cm²7.2 cm200 gVastus medialis

5 deg30 cm²6.7 cm210 gVastus lateralis

5 deg12.5 cm²6.8 cm90 gRectus femoris

5 deg9.1 cm²7.3 cm70 gTibialis anterior

15 deg21 cm²2.4 cm55 gTibialis posterior

15 deg30 cm²4.8 cm158 gGastrocnemius

30 deg58 cm²3.0 cm215 gSoleus

04.4 cm²16 cm75 gSemitendinosus

015.8 cm²9 cm150 gBiceps femoris

01.9 cm²38 cm75 gSartorius

Pennation anglePCAFiber lengthMassMuscle

Physiological Cross-section Area of some muscles

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Moments of musclesMoments of muscles

Depend on the force and on the moment Depend on the force and on the moment arm length (i.e. the normal line from the arm length (i.e. the normal line from the joint center to the muscle force vector).joint center to the muscle force vector).

Change with the joint angleChange with the joint angle

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Calculation of human movementCalculation of human movement

Get the anthropometric data

Get the mechanical properties of materials

Define the acting forces

Define the boundary conditions

Solve the equations of movement

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ExampleExample showingshowing thethe complexitycomplexity ofofanthropometricanthropometric datadata

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Example of presence of biomaterials in the tissues

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Forces acting on the kinetic chainsForces acting on the kinetic chains

GravityGravity : : fall, walking, divingfall, walking, divingFrictionFriction:resistance:resistance to body progression in air, to body progression in air, water...water...Muscle forceMuscle force under nervous system control:under nervous system control:push off in walking, push off in walking, antigravificantigravific, antagonist, , antagonist, agonistagonistInternal linking forces Internal linking forces (tension developed by (tension developed by ligaments and/or transmitted by contact surfaces)ligaments and/or transmitted by contact surfaces)Ground reaction, impact with obstaclesGround reaction, impact with obstacles

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Forces acting on the kinetic chainsForces acting on the kinetic chains

O2

uptake

CO2

expired

EXTERNAL WORK

maintenance heatheat of contraction, activation, labile stable, shortening

Metabolic energyMetabolic energy

Mechanical energyMuscle tension

Mechanical energyMuscle tension

loss due to cocontractionor absorption by muscles at another joint

Increase in segment energies

Increase in segment energies

The main difficulty is the force delivered by the muscle !!!

Scheme of energy flow through the muscles

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Equations of movementEquations of movement

Based on the classical laws of mechanicsBased on the classical laws of mechanicsDifferent levels of complexityDifferent levels of complexity

rigid body mechanics with jointsrigid body mechanics with joints(body decomposed into rigid elements with (body decomposed into rigid elements with kinematickinematicconstraints)constraints)

deformable solid mechanics with jointsdeformable solid mechanics with joints(the different elements of the body model can deform with (the different elements of the body model can deform with kinematickinematic constraints) constraints)

Use of Use of softwaressoftwares to solve the equationsto solve the equations