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Biomechanics Basics

Biomechanics Basics. Bio. Mechanics. Physical Therapy. Biomechanics. Ideal Fluids. Viscous Fluids. Fluids. Biological Systems Osseous Joints & Ligaments Muscles & Fasciae Cardiovascular CNS PNS Organs of senses Integumentary Respiratory Digestive Urogenital Lymphatic

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Biomechanics Basics

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  1. Biomechanics Basics

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

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

  4. Bio Mechanics Physical Therapy Biomechanics Ideal Fluids Viscous Fluids Fluids Biological Systems Osseous Joints & Ligaments Muscles & Fasciae Cardiovascular CNS PNSOrgans of senses Integumentary Respiratory Digestive Urogenital Lymphatic Ductless glands Compressible Fluids Material strength Deformable Bodies Elasticity Plasticity Solids Rigid Bodies Dynamics Statics Health profession Application of Scientific Principles Movement Dysfunction Clinical practice, research, education Pathology Prevention, evaluation, treatment Kinetics Kinematics From Smidt GL. Biomechanics and Physical Therapy. Physical Therapy. 64(12): 1807-08, 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 F1 F2 F2 F1 F3

  13. Force Systems • Concurrent • General F2 F1 F3 F1 F2 F4 F3

  14. Force Systems • Force Couple F2 F1

  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. 20 lbs. 12” Moment • T = F * ma • T = 20 lbs. * 12 in. • T = 240 in-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 - w = mg Biomechanics Book + 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. EA RA FR FE First Class Lever

  30. First Class Lever

  31. First Class Lever • few in body • Triceps on olecranon • Splenius Capitis on OA joint

  32. First Class Lever

  33. Mechanical Advantage • M. Adv. = FR / FE • M. Adv. = EA / RA (forces  levers) • M. Adv. > 1  advantage • M. Adv. < 1  disadvantage

  34. EA RA Second Class Lever

  35. FE FR Second Class Lever

  36. FE FR Second Class Advantage M. Adv. always > 1

  37. Second Class Lever Very few in body Heel raise (fixed distal segment) Eccentric: • G is FE • muscle is FR

  38. Second Class Lever

  39. EA FE FR RA Third Class Lever

  40. FE FR Third Class Lever

  41. FE FR Third Class Disadvantage M. Adv. always < 1

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

  43. Third Class Lever

  44. Inefficient Human Body? • 3rd class: FE  > movement of distal segment (goal) • 2nd class: FE (gravity)  < movement of distal segment  > 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/m2

  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 / L0 • Compressive,tensile, shear(angulation)

  49. T T C S Strain

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

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