Transcript
Page 1: Biomechanics concepts

BIOMECHANICS CONCEPTS

BIOMECHANICSStudy of Biological Systems by Means of Mechanical Principles

father of MechanicsSir Isaac Newton

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BIOMECHANICS

Biology

Skeletal system

Muscular system

Nervous system

Physics

Mechanics

Kinetics Kinematics

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HUMAN MOVEMENT ANALYSIS

BIOMECHANICS KINESIOLOGY

KINETICS FUNCTIONALKINEMATICS

Linear

Position Velocity

Acceleration

Position Velocity

Acceleration

Linear Angular

Force Torque

Angular

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Basic types of Motion Linear

Rectilinear Curvilinear

Angular or rotational Combined or general

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Human Analysis Internal: mechanical factors

creating and controlling movement inside the body

External: factors affecting motion from outside the body

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Kinematics Describes motion

Time Position Displacement Velocity Acceleration

Vectors Angular and linear quantities

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Kinematics Formulas Linear Motion Angular Motion

Symbol Equation Symbol Equation

Time t t=t2-t1 t t=t2-t1

Position (x,y) (r,)

Displacement d d=d2-d1

Velocity v v=d/t =/t

Acceleration a a=v/t =/t

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Kinetics Explains causes of motion

Mass amount of matter (kg)

Inertia: resistance to being moved Moment of Inertia (rotation) I = m·r2

Axis

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Kinetics Force: push or pull that tends to

produce acceleration Important factor in injuries Vector

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Kinetics Idealized force vector Force couple system

d= d

FF

F

F’

=d

F

M=Fd

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Kinetics: Force Force & Injury factors

Magnitude Location Direction Duration Frequency Variability Rate

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Kinetics: Force System Linear Parallel

Concurrent

General

Force Couple

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Center of Mass (COm) or Gravity (COG) It is an imaginary point where

there is intersection of all 3 cardinal plane.

Imaginary point where all the mass of the body or system is concentrated

Point where the body’s mass is equally distributed

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Pressure P = F/A Units (Pa = N m2) In the human body also

called stress Important predisposing

factor for injuries

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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

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Moments of Force (Torque) Force components

Rotation Stabilizing or destabilizing

component

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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

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Moments of Force (Torque) Large moments tends to produce injuries on the

musculo-skeletal system Structural deviation leads to different MA’s

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NEWTONIAN LAWS of Motion

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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

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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

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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

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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

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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)

dW W

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Mechanical Energy Capacity or ability to

do work Accounts for most

severe injuries Classified into

Kinetic (motion) Potential (position or

deformation)P.Ratan (MPT, Ortho & Sports)

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Kinetic Energy Body’s motion Linear or Angular

KE=.5·m·v2

KE=.5 ·I·2

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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

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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 )

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Momentum 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

P

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Angular Momentum Quantity of angular

motion H=I · (angular) Conservation of angular

momentum Transfer of angular

momentum

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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

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Friction Resistance between two bodies

trying to slide Imperfection of the surfaces Microscopic irregularities -

asperities Static friction

f< s·N Kinetic

f=µk·N N

f

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Friction Rolling: Lower that static and kinetic

friction (100-1000 times) Joint Friction - minimized Blood vessels - atherosclerosis

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FLUID MECHANICS

Branch of Mechanics Dealing with the Properties & Behaviors of Gases & Fluids

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Fluid Flow Laminar Turbulent Effects of friction on

arterial blood flow

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Fluid Forces Buoyancy Drag

Surface Pressure Wave

Lift Magnus forces Viscosity Biological tissue must have a fluid component

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Fluid Forces

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