Biomechanics Basics

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): , 1984.

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

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): , 1984.

Definition Kinematics Kinetics

Kinematic Variables Temporal characteristics Position or location Displacement Velocity Acceleration

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

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

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

Force (vector) Point of application Direction Magnitude

Mass Quantity of matter (kg) Center of Mass

Force Systems Linear Parallel F1F1 F2F2 F1F1 F2F2 F3F3

Force Systems Concurrent General F1F1 F2F2 F1F1 F3F3 F3F3 F2F2 F4F4

Force Systems Force Couple F1F1 F2F2

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

Pressure Force / Area

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

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

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

Moments Coxa Varum

Newton’s Laws of Motion

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

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

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

Law of Reaction Ground Reaction Forces

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

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

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

First Class Lever EARA FEFE FRFR

First Class Lever

few in body Triceps on olecranon Splenius Capitis on OA joint

First Class Lever

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

Second Class Lever EA RA

Second Class Lever FRFR FEFE

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

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

Second Class Lever

Third Class Lever EA RA FRFR FEFE

Third Class Lever FRFR FEFE

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

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

Third Class Lever

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

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

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

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

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)

Strain TT C S

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

Stress and Strain Slope =   /   as slope   stiffness 

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

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

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

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

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

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

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

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

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

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

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

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

Creep – FSU

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

Stress Relaxation

 t t0t0  t t0t0 Viscoelastic “Solid” Viscoelastic “Fluid”  t t0t0

Creep Effect of temp.  temp  rate of creep