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Chapter 3 Biomechanics Concepts I. Biomechanics: Study of biological systems by means of mechanical principles Sir Isaac Newton, father of Mechanics. Basic types of Motion. Linear rectilinear curvilinear Angular or rotational Combined or general. Human Analysis.

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chapter 3 biomechanics concepts i

Chapter 3 Biomechanics Concepts I

Biomechanics: Study of biological systems by means of mechanical principles

Sir Isaac Newton, father of Mechanics

basic types of motion
Basic types of Motion
  • Linear
    • rectilinear
    • curvilinear
  • Angular or rotational
  • Combined or general
human analysis
Human Analysis
  • Internal: mechanical factors creating and controlling movement inside the body
  • External: factors affecting motion from outside the body
kinematics
Kinematics
  • Describes motion
    • Time
    • Position
    • Displacement
    • Velocity
    • Acceleration
  • Vectors
  • Angular and linear quantities
kinetics
Kinetics
  • Explains causes of motion
    • Mass
      • amount of matter (kg)
    • Inertia: resistance to being moved
    • Moment of Inertia (rotation) I = m·r2

Axis

kinetics1
Kinetics
  • Force: push or pull that tends to produce acceleration
  • Important factor in injuries
  • Vector
kinetics2

d

Kinetics
  • Idealized force vector
  • Force couple system

F

F’

F

M=Fd

d

d

=

=

F

F

kinetics force
Kinetics: Force
  • Force & Injury factors
    • Magnitude
    • Location
    • Direction
    • Duration
    • Frequency
    • Variability
    • Rate
kinetics force system
Kinetics: Force System
  • Linear
  • Parallel
  • Concurrent
  • General
  • Force Couple
center of mass or gravity
Center of Mass or Gravity
  • Imaginary point where all the mass of the body or system is concentrated
  • Point where the body’s mass is equally distributed
pressure
Pressure
  • P = F/A
  • Units (Pa = N m2)
  • In the human body also called stress
  • Important predisposing factor for injuries
moments of force torque
Moments of Force (Torque)
  • Effect of a force that tends to cause rotation about an axis
  • M = F ·d (Nm)
    • If F and d are 
  • Force through axis
moments of force torque1
Moments of Force (Torque)
  • Force components
    • Rotation
    • Stabilizing or destabilizing component
moments of force torque2
Moments of Force (Torque)
  • Net Joint Moment
    • Sum of the moments acting about an axis
  • Human: represent the muscular activity at a joint
    • Concentric action
    • Eccentric action
    • Isometric
moments of force torque3
Moments of Force (Torque)
  • Large moments tends to produce injuries on the musculo-skeletal system
  • Structural deviation leads to different MA’s
1 st law of motion
1st Law of Motion
  • A body a rest or in a uniform (linear or angular) motion will tend to remain at rest or in motion unless acted by an external force or torque
  • Whiplash injuries
2 nd law of motion
2nd Law of Motion
  • A force or torque acting on a body will produce an acceleration proportional to the force or torque
  • F = m ·a or T= I ·

F

3 rd law of motion
3rd Law of Motion
  • For every action there is an equal and opposite reaction (torque and/or force)
  • Contact forces: GRF, other players etc.

GRF

equilibrium
Equilibrium
  • Sum of forces and the sum of moments must equal zero
    •  F = 0
    •  M = 0
  • Dynamic Equilibrium
    • Must follow equations of motions
    •  F = m x a
    •  T = I x 
work power
Work & Power
  • Mechanical Work
    • W= F ·d (Joules)
    • W= F ·d·cos ()
  • Power: rate of work
    • P = W/t (Watts)
    • P = F ·v
    • P = F ·(d/t)

d

W

mechanical energy
Mechanical Energy
  • Capacity or ability to do work
  • Accounts for most severe injuries
  • Classified into
    • Kinetic (motion)
    • Potential (position or deformation)
kinetic energy
Kinetic Energy
  • Body’s motion
  • Linear or Angular
    • KE=.5·m·v2
    • KE=.5 ·I·2
potential energy
Potential Energy
  • Gravitational: potential to perform work due to the height of the body
    • Ep= m·g·h
  • Strain: energy stored due to deformation
    • Es= .5·k·x2
total mechanical energy
Total Mechanical Energy
  • Body segment’s: rigid (nodeformable), no strain energy in the system
  • TME = Sum of KE, KE, PE

TME = (.5·m ·v2)+(.5 ·I ·2)+(m ·g ·h )

momentum
Momentum

P

  • Quantity of motion
  • p=m ·v (linear)
  • Conservation of Momentum
  • Transfer of Momentum
  • Injury may result when momentum transferred exceeds the tolerance of the tissue
  • Impulse = Momentum
angular momentum
Angular Momentum
  • Quantity of angular motion
  • H=I · (angular)
  • Conservation of angular momentum
  • Transfer of angular momentum
collisions
Large impact forces due to short impact time

Elastic deformation

Plastic deformation (permanent change)

Elasticity: ability to return to original shape

Elastoplastic collisions

Some permanent deformation

Transfer and loss of energy & velocity

Coefficient of restitution

e=Rvpost/Rvpre

Collisions
friction
Friction
  • Resistance between two bodies trying to slide
  • Imperfection of the surfaces
  • Microscopic irregularities - asperities
  • Static friction
    • f<s·N
  • Kinetic
    • f=µk·N

f

N

friction1
Friction
  • Rolling: Lower that static and kinetic friction (100-1000 times)
  • Joint Friction - minimized
  • Blood vessels - atherosclerosis
fluid mechanics

Fluid mechanics

Branch of mechanics dealing with the properties and behaviors of gases & fluids

fluid flow
Fluid Flow
  • Laminar
  • Turbulent
  • Effects of friction on arterial blood flow
fluid forces
Fluid Forces
  • Buoyancy
  • Drag
    • Surface
    • Pressure
    • Wave
  • Lift
  • Magnus forces
  • Viscosity
  • Biological tissue must have a fluid component