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Biomechanics Basics. Biomechanics Bio Mechanics Physical Therapy Biological Systems Osseous Joints & Ligaments Muscles & Fasciae Cardiovascular CNS PNS.

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Presentation on theme: "Biomechanics Basics. Biomechanics Bio Mechanics Physical Therapy Biological Systems Osseous Joints & Ligaments Muscles & Fasciae Cardiovascular CNS PNS."— Presentation transcript:

1 Biomechanics Basics

2 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.

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

4 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.

5 Definition Kinematics Kinetics

6 Kinematic Variables Temporal characteristics Position or location Displacement Velocity Acceleration

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

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

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

10 Force (vector) Point of application Direction Magnitude

11 Mass Quantity of matter (kg) Center of Mass

12 Force Systems Linear Parallel F1F1 F2F2 F1F1 F2F2 F3F3

13 Force Systems Concurrent General F1F1 F2F2 F1F1 F3F3 F3F3 F2F2 F4F4

14 Force Systems Force Couple F1F1 F2F2

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

16 Pressure Force / Area

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

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

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

20 Moments Coxa Varum

21 Newton’s Laws of Motion

22 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

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

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

25 Law of Reaction Ground Reaction Forces

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

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

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

29 First Class Lever EARA FEFE FRFR

30 First Class Lever

31 few in body Triceps on olecranon Splenius Capitis on OA joint

32 First Class Lever

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

34 Second Class Lever EA RA

35 Second Class Lever FRFR FEFE

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

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

38 Second Class Lever

39 Third Class Lever EA RA FRFR FEFE

40 Third Class Lever FRFR FEFE

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

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

43 Third Class Lever

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

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

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

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

48 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)

49 Strain TT C S

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

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

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

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

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

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

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

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

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

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

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

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

62 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

63 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

64 Creep – FSU

65

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

67 Stress Relaxation

68

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

70 Creep Effect of temp.  temp  rate of creep


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