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Biomechanics Basics

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Biomechanics Bio Mechanics Physical Therapy Biological Systems Osseous Joints & Ligaments Muscles & Fasciae Cardiovascular CNS PNS Organs of senses Integumentary Respiratory Digestive Urogenital Lymphatic Ductless glands Health profession Application of Scientific Principles Movement Dysfunction Clinical practice, research, education Pathology Prevention, evaluation, treatment Fluids Ideal Fluids Viscous Fluids Compressible Fluids Solids Deformable Bodies Material strength Elasticity Plasticity Rigid Bodies StaticsDynamics Kinematics Kinetics From Smidt GL. Biomechanics and Physical Therapy. Physical Therapy. 64(12): 1807-08, 1984.

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Biomechanics Study of mechanics in the human body Mechanics statics – bodies @ rest or moving w/ constant velocity dynamics – bodies in motion undergoing acceleration

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Biomechanics Bio Mechanics Physical Therapy Biological Systems Osseous Joints & Ligaments Muscles & Fasciae Cardiovascular CNS PNS Organs of senses Integumentary Respiratory Digestive Urogenital Lymphatic Ductless glands Health profession Application of Scientific Principles Movement Dysfunction Clinical practice, research, education Pathology Prevention, evaluation, treatment Fluids Ideal Fluids Viscous Fluids Compressible Fluids Solids Deformable Bodies Material strength Elasticity Plasticity Rigid Bodies StaticsDynamics Kinematics Kinetics From Smidt GL. Biomechanics and Physical Therapy. Physical Therapy. 64(12): 1807-08, 1984.

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Definition Kinematics Kinetics

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Kinematic Variables Temporal characteristics Position or location Displacement Velocity Acceleration

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Linear versus Angular Kinematics Position or location Displacement (d vs. ) Velocity (v vs. ) Acceleration (a vs. )

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Kinetics Forces Mechanical action or effect applied to a body that tends to produce acceleration Push or pull

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Kinetics - Forces Mutual interaction between 2 bodies - produces deformation of bodies and/or - affects motion of bodies

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Force (vector) Point of application Direction Magnitude

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Mass Quantity of matter (kg) Center of Mass

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Force Systems Linear Parallel F1F1 F2F2 F1F1 F2F2 F3F3

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Force Systems Concurrent General F1F1 F2F2 F1F1 F3F3 F3F3 F2F2 F4F4

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Force Systems Force Couple F1F1 F2F2

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Center of Mass/Gravity Point at which body’s mass is equally distributed Balance point

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Pressure Force / Area

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Moment or Force / Torque (T) Degree to which a force tends to rotate an object Torque twist Moment bend

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Moment or Force / Torque (T) T = f * ma ma = moment arm, lever arm, torque arm Shortest distance ( ) from AOR to line of force

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Moment T = F * ma T = 20 lbs. * 12 in. T = 240 in-lbs. 12” 20 lbs.

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Moments Coxa Varum

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Newton’s Laws of Motion

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Law of Inertia (1) Body at rest or in uniform motion will tend to remain at rest or in uniform motion unless acted upon by an external force

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Law of Acceleration (2) a f causing it Acceleration acts in same direction as f f = m * a

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Law of Reaction (3) Every action = & opposite reaction Biomechanics Book - w = mg + w = mg

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Law of Reaction Ground Reaction Forces

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Equilibrium At rest (static) or Constant linear/angular velocities (dynamic) Sum of forces = 0 (3d) Sum of moments = 0 (3d)

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Work and Power Work = Force * distance Power = Work / time

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Momentum “quantity of motion” p = m * v (linear) Bigger & faster they are, the harder they hit

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First Class Lever EARA FEFE FRFR

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First Class Lever

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few in body Triceps on olecranon Splenius Capitis on OA joint

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First Class Lever

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Mechanical Advantage M. Adv. = F R / F E M. Adv. = EA / RA (forces levers) M. Adv. > 1 advantage M. Adv. < 1 disadvantage

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Second Class Lever EA RA

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Second Class Lever FRFR FEFE

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Second Class Advantage M. Adv. always > 1 FRFR FEFE

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Second Class Lever Very few in body Heel raise (fixed distal segment) Eccentric: G is F E muscle is F R

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Second Class Lever

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Third Class Lever EA RA FRFR FEFE

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Third Class Lever FRFR FEFE

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Third Class Disadvantage M. Adv. always < 1 FRFR FEFE

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Third Class Lever Most common Concentric contractions Exchange between 2 nd and 3 rd class levers

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Third Class Lever

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Inefficient Human Body? 3 rd class: F E > movement of distal segment (goal) 2 nd class: F E (gravity) control

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Forces Acting on Human Internal - muscles, ligaments, tendons, bones External - Gravity, wind, water, another person

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Stress Internal resistance of a material to an imposed load = force / area Pascal = 1 N/m 2

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Axial Stress Axial (Normal) stress ( ) - compressive - tensile Shear stress ( ) - forces acting parallel or tangential

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Strain Change in shape or deformation as a result of an imposed external load/stress shape / original shape L / L 0 Compressive,tensile, shear(angulation)

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Strain TT C S

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Linear Stress-Strain Curves Stress ( ) Strain ( ) A B

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Stress and Strain Slope = / as slope stiffness

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Stress and Strain Elastic Region Yield Point or Elastic Limit Ultimate Failure or Fracture Point Strain or Deformation( ) Stress or Load ( ) Plastic Region

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Stress and Strain Elastic Region stiffness Young’s Modulus (E) = slope in elastic region E = /

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Mechanical Stress and Strain Wet Bone Stress Strain Dry Bone Glass Aluminum Steel

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Poisson’s Effect/Ratio C TT Applied compressive load tensile stress & strain

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Poisson’s Effect/Ratio Applied tensile load compressive stress & strain T T CC

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Poisson’s Ratio = - (transverse strain / axial strain) = - ( t / a )

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Viscoelasticity Viscosity resistance to flow ability to lessen shear force Elasticity ability to return to original shape after deforming load is removed

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Viscoelasticity Purely elastic – returns to original shape w/ no energy loss Load (deform) Unload (return)

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Viscoelastic Delayed return response and loss of heat energy (hysteresis) Load (deform) Unload (return)

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Viscoelastic Elastic effects - rate of elastic return dependent on material properties Viscous effects (time-dependent properties) - Creep - Stress-Relaxation

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Creep Test Material/tissue is subjected to a sudden, constant load ( ) Constant is maintained Deformation ( ) is recorded over time Measure of viscoelastic nature of material

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Creep Tissue deforms rapidly 2 0 sudden load (elastic) Continues to deform or creep beyond initial deformation (viscous) Definition – material deforms as a function of time under the action of a constant load

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Creep – FSU

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Stress Relaxation Constant strain ( ) level Develops an initial resistance or stress at that held deformation At that held deformation the stress ( ) or relaxes

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Stress Relaxation

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t t0t0 t t0t0 Viscoelastic “Solid” Viscoelastic “Fluid” t t0t0

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Creep Effect of temp. temp rate of creep

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