Download - Biomechanics Basics
Biomechanics Basics
Biomechanics
Bio Mechanics
PhysicalTherapy
Biological SystemsOsseousJoints & LigamentsMuscles & FasciaeCardiovascularCNSPNSOrgans of sensesIntegumentaryRespiratoryDigestiveUrogenital LymphaticDuctless glands
Health professionApplication of Scientific PrinciplesMovement DysfunctionClinical practice, research, educationPathologyPrevention, evaluation, treatment
FluidsIdeal FluidsViscous FluidsCompressible Fluids
Solids
DeformableBodies
Material strengthElasticityPlasticity
Rigid Bodies
StaticsDynamics
Kinematics Kinetics
From Smidt GL. Biomechanics and Physical Therapy.Physical Therapy. 64(12): 1807-08, 1984.
Biomechanics
Study of mechanics in the human body
Mechanics statics – bodies @ rest or moving w/
constant velocity dynamics – bodies in motion
undergoing acceleration
Biomechanics
Bio Mechanics
PhysicalTherapy
Biological SystemsOsseousJoints & LigamentsMuscles & FasciaeCardiovascularCNSPNSOrgans of sensesIntegumentaryRespiratoryDigestiveUrogenital LymphaticDuctless glands
Health professionApplication of Scientific PrinciplesMovement DysfunctionClinical practice, research, educationPathologyPrevention, evaluation, treatment
FluidsIdeal FluidsViscous FluidsCompressible Fluids
Solids
DeformableBodies
Material strengthElasticityPlasticity
Rigid Bodies
StaticsDynamics
Kinematics Kinetics
From Smidt GL. Biomechanics and Physical Therapy.Physical Therapy. 64(12): 1807-08, 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
F1 F2
F1F2
F3
Force Systems
Concurrent
General
F1
F2
F1
F3
F3
F2 F4
Force Systems
Force Couple
F1
F2
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
EA RA
FEFR
First Class Lever
First Class Lever few in body
Triceps on olecranon
Splenius Capitis on OA joint
First Class Lever
Mechanical Advantage M. Adv. = FR / FE
M. Adv. = EA / RA (forces levers)
M. Adv. > 1 advantage M. Adv. < 1 disadvantage
Second Class Lever
EA
RA
Second Class Lever
FR
FE
Second Class Advantage
M. Adv. always > 1
FR
FE
Second Class Lever
Very few in body
Heel raise (fixed distal segment)
Eccentric: G is FE
muscle is FR
Second Class Lever
Third Class Lever
EA
RAFR
FE
Third Class Lever
FR
FE
Third Class Disadvantage
M. Adv. always < 1
FR
FE
Third Class Lever Most common
Concentric contractions
Exchange between 2nd and 3rd class levers
Third Class Lever
Inefficient Human Body? 3rd class:
FE > movement of distal segment (goal)
2nd class:FE (gravity) < movement of
distal segment > 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/m2
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 / L0
Compressive,tensile, shear(angulation)
Strain
TT
C
S
Linear Stress-Strain Curves
Str
ess
()
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()
Str
ess
or L
oad
()
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
C C
Poisson’s Ratio = - (transverse strain / axial
strain)
= - (t / a)
Viscoelasticity
Viscosity resistance to flow ability to lessen shear forceElasticity ability to return to original
shape after deforming load is removed
Viscoelasticity
Purely elastic – returns to original shape w/ no energy loss
Load (defo
rm)
Unload (return)
Viscoelastic Delayed return response and loss
of heat energy (hysteresis)
Load (d
eform
)
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 20 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
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
Stress Relaxation
Stress Relaxation
tt0
tt0
Viscoelastic “Solid”Viscoelastic “Fluid”
tt0
Creep Effect of temp.
temp rate of creep