INTRODUCTIONF FOR BIOMECHANICS

ByAbdulgalil Allam

When we study any part of knowledge we ask ourselves these questions

• WhatIs the application of mechanical principles on the

living organisms.• WhyVia this science we able to solve many medical

problems that face the patients• HowUsing it on designing exercise programs, orthotics

and prosthesis, application of a technique etc… even when we give an advice to a patient.

Course Contents

• Forces• Centre of Gravity (COG).• Stability and Equilibrium.• Force Systems.• Simple Body Mechanics.• Motion and Newton’s laws.

• Biomechanics of bone.• Behaviour of bone under stress.• Stress strain curve.• Possible fracture patterns.• Various loading modes.

• Biomechanics of fracture fixation.• Soft tissue biomechanics(muscle and

cartilage)• Regional biomechanics: hip, knee, shoulder,

spine.• normal Gait.• Pathomechanics of Gait.• Mechanics of Posture.

Kinesiology &Biomechanics

• Kinesiology is the scientific study of human motion. (kinesis and ology)

• Biomechanics Is the application of mechanical principles on the living organisms.

Forces

• Definition:Physical quantity that tends to change state or

shape of an object ( state means the speed or equilibrium). So force can generate, stop, or modify motion.

It’s unit is Newton (N).

Force is a vector quantity

That because it has a magnitude and direction.Represented graphically by an arrow(vector) has

four characteristics:1-Magnitude length2-Direction head3-point of application tail4-line of application angle with the

horizontal (angle of pull).

A Vector representing a force

(1)

(2)

(3)(4)

Gravitational force

The force that attract any object to the Earth.The force by the gravity on an object is equal to

its weight . W = M x (g)

(in Newton) (in kg)Where g=9.8m/s or =10 N/kg 2

• Magnitude= the weight of the body.• Direction= downward.• Point of application= the center of gravity.• Line of application= 90 angle (perpendicular to

the ground)(COG is an imaginary point that the body weight can be assumed

to be concentrated and equally distributed.)

Ground Reaction Force

• Magnitude = gravity.• Direction opposite to gravity.• Line of application= gravity.• Point of application= point of contact to the

ground.

Frictional force

It’s the resistance force generated when two surfaces pressed and slide on each others.

• Magnitude= the pressure and coefficient of friction (µ) roughness.

• Direction=lateral.• Point of application= the surface of contact.• Line of application= parallel to the surface

pressure

Definition: It is the total force applied per unit area.

P=F/A

Measured in (N/m2 ) or pascal

Resistance

force that tends to reduce or stop a moving object

As air or water resistance, it depends mostly on the surface area

Center Of Gravity(COG)

Definition:(center of mass) COG is an imaginary point that the body weight

can be assumed to be concentrated and equally distributed, around which body can rotate freely in all direction.

At which summation of all moments equal zero

Location of COG

• Depends on the body’s shape and position.• In objects possess a symmetrical shape and

it’s mass are equally distributed it is located exactly in the center.

• For asymmetrical irregular bodies the COG will be nearer the larger and heavier end.

• In normal standing adult person its located anterior to the second sacral vertebra.

Factors affect the location of COG in the human body

1. Age• In newborn: above the umbilicus.• At two years: at level of umbilicus.• At five years: below the level of the umbilicus.• In adults: anterior to the 2nd sacral vertebra.

2-Sex

The COG in males is higher than in femalesBecause of

The different mass distribution

3- position of any part in relation to the others

COG is always shifts to the heavy mass

e.g. flexion and extension

running.

4-Addition and subtraction of weight

• By carrying a weight • Pregnancy• amputation