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Biomechanics
Socrates, born 2400 years ago, taught that we could not begin to understand the world around us until we understood our own nature.
As scientists who seek knowledge of the mechanics within their own bodies, and those of other living creatures, we share something of Socrates' inward inquiry.
Fortunately, we do not share the public abuse that he suffered, and which led him, as an old man of 70, to be tried, convicted, and executed for "impiety and corrupting the youth of Athens."
Introduction
Newly developed discipline of science.
Definition by Hay(1973)- Biomechanics is the science that examines forces acting upon and within a biological structure and effects produced by such forces.
External forces upon a system are quantified using sophisticated measuring devices.
Internal forces which result from muscle activity are assessed using implant measuring devices.
Possible results of these forces are:
Movement of segments of interest
Deformation of biological material
Biological changes in the tissues on which they act.
Hatze stated in (1971) Biomechanics is a science which studies structures and functions of biological system using the knowledge and methods of mechanics.
Biomechanical research addresses different areas like studies on
1. the functioning of muscles, tendons, ligaments, cartilage and bone.
2. load and overload of specified structures of living systems.
3. factors influencing performance.
Historical Highlights
Antiquity 650B.C.-200 B.C.
Middle Ages 200B.C.-1450A.D
Italian Renaissance 1450 A.D-1600 A.D
Scientific Revolution 1600 A.D-1730 A.D.
Enlightenment 1730 A.D-1800 A.D
The Gait Century 1800 A.D- 1900 A.D
The 20th century 1900 A.D…………..
The Scientific Legacy of Antiquity
Greek Sculpture illustrated the dynamics of movement and a working knowledge of surface anatomy.
Pythagorus (582 BC) experimented with shapes and numbers which resulted in famous theorem a2+b2=c2.
His disciples were divided into two hierarchical groups: the scientists (ask questions and postulate ideas) and listeners (study).
According to him “… all things have form and forms can be defined by numbers…”.
His arithmetic was based on dots drawn on pebbles.
He regarded the universe and human body as musical instrument whose string required balance and tension to produce harmony.
The execution of Socrates had a profound affect on Plato, 51 years his junior .
Plato(427-347 BC) believed that mathematics, a system of pure ideas, was the best tool for the pursuit of knowledge.
Universe was the subject to power of divine creator.
At age 17, Aristotle went to Athens to study at Plato's academy.
His father served as a physician to the grandfather of Alexander.
Aristotle’s (384-322 BC) universe consisted of four observable elements: fire, air, water and earth.
Aristotle had a remarkable talent for observation and was fascinated by anatomy and structure of living things.
Indeed, Aristotle might be considered the first biomechanician.
He wrote the first book called "De Motu Animalium" - On the Movement of Animals.
He not only saw animals' bodies as mechanical systems, but pursued such questions as the physiological difference between imagining performing an action and actually doing it.
Herophilos (300 BC) initiated the foundation of modern anatomy by creating a sytematic approach to dissection, identifying numerous organs.
He revived the belief that brain is the seat of intelligence and not heart as suggested by Aristotle.
Archimedes (287-212 BC) using his compound pulley and lever, claimed that he would be able to move the earth, if only he had a place to stand in order to do so.
Archimedes treatise Floating bodies described the principle of water displacement (while bathing). Was killed at spot by roman soldier for he was absorbed in geometrical figures and shouted “keep off”

Galen (129-201 AD) was the first sports physician and team doctor in history.
His voracious appetite for learning, exceptional brilliance, overriding ambitions and energetic and violent nature impressed the world.
He performed surgeries and dissections and published some 500 medical treatises.
His majority of manuscripts were destroyed in a fire at a temple.
Relevance to Biomechanics
The relevance of antiquity to biomechanics lies in three major aspect;
Knowledge and Myth were separated
Mechanical and Mathematical Paradigms were developed
First biomechanical analysis of human body was performed.
Middle ages
Arab scholars saved the scientific investigations of antiquity from disappearing completely by translating the works from Greek to Arabic.
St. Augustine discouraged the scientific enquiry and explained that knowledge of God is the only type of knowledge.
Medicine existed but human locomotion was discouraged.
Relevance to Bio-Mechanics
The relevance of the middle ages to the development is minimal.
The development was discouraged and put to sleep for more than 1200 years.
The Italian Renaissance
Leonardo the Vinci (1452-1519) was a military and civil Engineer.
His versatile talent reflected into his inventions.
It includes distillation apparatus, a helicopter, a parachute, etc.
He described parallelogram of forces, Ball and socket joints at shoulders and hip joint.
Shoulder joint in Da Vinci’s study
He was a self taught man and criticized others for relying on others ideas.
He worked as an apprentice to Verrochio an artist.
He surpassed his teacher who vowed never to touch another brush.
First publication of his work occurred 250 years after his death.
Picture of eye and brain which combines Greek and Arab views
Vesalius (1514-1564) received his formal training in medicine.
Performed human dissections to re-evaluate the anatomy of muscles.
He believed the muscles to be composed of ligaments and tendons which are divided into great number of fibres.
He challenged Galen’s anatomy.
Human skeleton from Vesalius’s book
Relevance to Biomechanics
Scientific work was revived.
The foundation for modern anatomy and physiology were laid.
Movement and muscle action were studied.
Scientific revolution
In 17th century, Galileo Galilei(1564-1642), Johannes Kepler (1571-1630), Issac newton (1642-1727) tried to understand the nature and the way of doing scientific analysis.
Galileo shaped the path of science for centuries to come.
Newton admitted, “If I had been able to see farther it is because I stood on the shoulders of giants.”
Galileo studied the biomechanics of human jump, gait analysis of horses and insects, effect of changing the structures of biological materials.
Santorio(1561-1636) colleague of Galileo, taught theoretical medicine at University of Padua.
He was the first to apply mechanics to medicine.
For 30 years, he spent much of his time suspended from a steelyard weighing himself and his solid and liquid inputs and outputs.
He laid the foundation for metabolism.
Santorio in his balance
William Harvey (1578-1657) studied the motion of heart.
He discovered the circulation of blood.
He applied theory of mechanics to heart and described its function as a pump.
He became first cardiac biomechanist.
And later died of stroke
Rene Descartes (1596-1650) serving as a soldier in Holland, invented cartesian coordinate system.
By observing the habits of a fly zooming in the room while lying in the bed.
This developed a habit of sleeping late in night.
He was a tutor to Queen Christina who preferred studying at 5:00 am in freezing cold library.
Within five months he died of lung disease.
Giovanni Borelli (1608-1679) was holding a degree in medicine and mathematics.
His investigations of mechanics of human body led him to be known as father of Biomechanics.
He integrated physics and physiology. He formulated hypothesis which included:
The trajectory of jump is parabolic.
Why a jump during running is longer and higher.
Muscle contraction does not consist of simple tension of the fibres similar to that exerted on a rope raising a weight.
He prepared Borelli’s table, the movement of Animals: illustrating the models of muscular construction.
On Dec 25th 11 months after Galileo’s death, Issac Newton (1642-1727) was born.
His contributions are;
Explained Kepler’s law of motion of heavenly bodies.
Explained Galileo’s law of falling bodies and projectiles.
Explained Descartes law of inertia.
Laws of motions
He discovered the theory of gravitation and misplaced it for 20 years when his interest turned to alchemy.
He reformed currency and was president of royal society.
However he was ridiculed and satirized as a scientist who concentrated on unimportant facts etc.
Relevance to Biomechanics
Experiment and Theory were introduced as complimentary elements in scientific investigations.
The Newtonian Mechanics were established providing a complete theory for mechanical analysis.
The Enlightment
Newton’s laws were analysed.
Discarded by few and appreciated by few.
40 books on Newton in English,17 in french and 3 in German.
D’ Alembert (1717-1783) stated that Newton’s third law holds true for fixed bodies and free bodies both.
Motion of rigid bodies was studied by Daniel Bernoulli and Leonhard Euler.
Euler is considered as ablest, most brilliant and productive scientist and mathematician of 18th century.
John Hunter (1728-1793) analysed that muscles are fitted for self motion and are the only body part so fitted.
Robert Whytt(1714-1793) did the first demonstration of reflex action by spinal cord.
Relevance to Biomechanics
The concept of force was clearly understood.
The concept of conservation of momentum and energy started to develop.
Mathematical consolidation of different mechanical laws took place.
Muscle contraction and action became an event influenced by mechanical, biochemical and electrical forces.
Gait century
Invention of steam engine started the industrial revolution.
Jean Jacques Rousseau’s (1712-1778) novel Emile revived the ancient idea of development of body and intellect by physical activity.
It was proposed that exercise during childhood could prevent musculo-skeleton deformities in adulthood.
Volkmann described the effect of pressure on bone growth in 1862.
In 1867 Van Meyer described the relation between the architecture of bone and its function.
Development of sports and leisure during late 18th century created a renewed scientific interest in human locomotion.
Analysis of human Gait occupied physiotherapist, engineers, mathematicians and adventurers.
Weber brothers published 150 hypotheses about human Gait which were derived from observation and theoretical considerations.
Some of them were correct others incorrect,
Primary importance is not in correctness but in establishing an agenda for further research.
Study of locomotion started as an observational science.
By the end of 19th century, photography had revolutionized and quantified the study of human and animal movement.
Etienne Marey (1838-1904) was more recognised as pioneer of cinematography than of biomechanics.
He developed modern cinecamera.
Marey suggested frame by frame analysis of movements arguing that screen portrayed images which he could not see with his own eyes.
He illustrated the movements he analyzed from film recordings with scientific drawings.
Braune and Fischer’s publication contained mathematical analysis of 3 transits of human gait including 2 on free walking and 1 walking with army knapsack, 3 full cartridge pouches and 88 rifles on shoulder arm position.
Reymond laid the foundation of electromyography.
Engineering principles were introduced to understand the bone physiology.
Relevance to Biomechanics
Measuring methods were developed to quantify kinematics and kinetics of movement and applied to human Gait analysis.
Measuring methods were developed to quantify electrical current during muscular activity.
Engineering principles were applied to biological and biomechanical analysis.
The 20th century
The 20th century was characterized by several factors which affected the development of Biomechanics:
Mechanical and technological development resulting from two world wars.
Increased popularity, social and financial recognition of sports in society.
Financial support for medical and healthcare research.
In 1920 Jules Amar published his book The Human Motor.
This was an analysis of physical and physiological components of work, taking into consideration the worker’s environment and individual movements.
Nicolas Bernstein’s (1896-1966) analysis of coordination and regulation of movement provided the basis for theories of motor control.
Einstein developed theory of relativity(1905).
A.V.Hill a mathematician switched off to physiology and received a Nobel Prize.
He developed theories for mechanical and structural function of human muscle.
Rudolph Laban developed a method of representing a series of complex human movements which are still used for dance choreography.
Elftman estimated internal forces in muscles and joints.
Huxley studied physics and worked on Radar in World war II.
He gained recognition for his work with the model of muscle contraction and development of X ray diffraction and electron microscopy.
In 1967 first international seminar on biomechanics was held with the discussions on following topics;
Techniques of motion studies,
Telemetry,
Principles of coordinations of human motion,
Applied biomechanics in work and sports,
Clinical aspect.
Research dealing with movement, exercise and sport, of which biomechanics is a substantial part, now has a prestigious international prize.
The IOC- Olympic prize.
It is awarded every two years in connection with Olympic Games.
The first Prize was awarded in 1996 in Atlanta.
This award to a biomechanist is an indication of increasing importance of this science and biomechanical research performed world wide.
Relevance to biomechanics
Biomechanics developed as a discipline at universities.
Biomechanical research results were increasingly used in practical, medical and industrial applications.
Biomechanics became a player in multidisciplanary attempt to understand human and animal movements.
Final comments
MECHANICS
We have seen footballs bouncing and wheels rolling.
The branch of science dealing with the effect of forces on bodies is called Mechanics.
When Mechanics is applied in Engineering, design and analysis of mechanisms and machine, it is called as Engineering Mechanics.
When bodies interact and forces act between them there are two possibilities, they may move or they may remain static.
Definition
The branch of Engineering Mechanics dealing with the motion of bodies is called as Dynamics.
the other branch is called as Statics, in which we study balance and equilibrium of bodies.
Statics
This branch of mechanics deals with bodies in equilibrium and are not moving with respect to the frame of reference considered for analysis.
Bodies may be experiencing different forces but the configuration of these forces is such that the resultant force on the system is zero.
The unbalanced forces tend to accelerate a body but if net force is zero the body will not.
In addition to accelerating a body, forces make bodies rotate.
This ability of a force to rotate a body is called as torque or moment of the force.
For true static equilibrium the net moment or torque on a body should also be zero along with zero net force.
Dynamics
The analysis of forces and motion in moving bodies comes in Dynamics.
Divided in two branches, kinematics and kinetics.
Kinematics deals with the analysis of motion of bodies without considering the forces causing or associated with these motions.
In this, the position, velocity and acceleration of certain points and the members of mechanisms and machines is studied.
The forces causing motion in bodies are studied under kinetics.
The concept of work and energy, and its application for analysis of mechanical systems also comes in this branch of dynamics.
Classical mechanics is the study of the motion of bodies (including the special case in which bodies remain at rest) in accordance with the general principles.
First enunciated by Sir Isaac Newton.
Solid Mechanics is the study of load carrying members in terms of forces, deformations, and stability.
Typesof motion in Classical mechanics
Translational (e.g., the motion of a bullet from a gun).
Rotational motion (e.g., the motion
of a spinning top).
Oscillatory motion. (e.g., the motion of a pendulum in a grandfather clock).
Circular motion. [e.g., the (approximate) motion of the Earth about the Sun].
First law: If F=0 then v=constant
Unless acted upon by a net external force, a body, at rest, will remain at rest and a body, in motion, will remain in motion.
Second law: F=m.a
An unbalanced force acting on an object will result in the object's momentum changing over time.
Third law: F12=-F21
Every action has equal and opposite reaction.
Density: mass per unit volume
Stress: force acting per unit area.
Yeild stress: the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed.
Ultimate stress: Maximum stress at a point where it can withstand maximum load before failure.
DOF: Min no. of variables required to specify all positions and orientations of the body.
Elastic modulus(E): ratio of stress to strain
Shear modulus(G): Ration of shear stress to shear strain
Bulk Modulus(K): Ratio of volumetric stress to volumetric strain
Poisson’s ratio(μ): Ratio of Lateral strain to longitudinal strain
Relations
Load : sum of all forces and moments
Cyclic load: A load that changes its value by following regular repeating sequence of change
Properties: which describe the material
Material properties: which describes its general behaviour
Physical properties: properties related to physics
Structural properties: Properties of a sample which includes size and shape.
Chemical properties:
Properties describing the chemistry of a material
Strain:
ratio of change in dimension to its original dimension
Engg strain:
deformation divided by original length
True strain:
deformation divided by instantaneous length.
Strain Rate:
change of strain over time
Strength:
Maximum force a material can withstand before failure
Isotropy:
A term indicating equal physical and material properties in all direction
Orthrotopy:
A property due to which material exhibits different properties in three mutually perpendicular directions.
Anisotropy:
A variation in material property with respect to direction
Type of behavior
Linear
A material in which some specified influence (such as stress, electric -field, or magnetic field) produces a response (such as strain, electric polarization, or magnetization) which is proportional to the influence.
Non linear
Output is not proportional to input
Elasticity
the ability to temporarily change shape, but return to the original shape when the force is removed.
Plasticity—
the ability to permanently change shape in response to the force, but remain in one piece.
Deformation in the plastic range is non-linear.
Viscosity
Resistance of a fluid to a change in shape, or movement of neighbouring portions relative to one another.
Viscosity denotes opposition to flow.
Visco-elasticity
Some materials exhibit both elasticity and viscosity when undergoing plastic deformation;
Deformation: Localized or overall change in the shape of member due to force or results in alteration of force system.
Change in distance between particles reflects normal deformation.
If distance increases, deformation is tensile;
If it decreases it is compressive.
If angle between two lines or layers changes, deformation is shear.
Bending
Defined as a shape change from straight to curved configuration.
It is measured by a tranverse deflection.
Twisting
Defined as change in orientation of transverse reference line.
It is measured by an angular deformation.
Stiffness:
The stiffness of a body is a measure of the resistance offered by an elastic body to deformation (bending, stretching or compression).
slope of the linear area of load deformation curve.
Toughness:
Toughness is defined as the resistance of a material to fracture at small plastic deformations under stress.
Fracture toughness
A property which describes the ability of a material containing a crack to resist fracture.
Total area under load deformation diagram
Resilience:
It is the maximum energy per unit volume that can be elastically stored.
Area under load deformation curve upto elastic limit
Ductility:
Signifies how severe permanent bend a wire can sustain without fracture
Brittleness:
Fracture point and elastic limit point coincides for perfectly brittle material.
Friction
Resistance to the movement tangent to the contact area of one material relative to the other is called Friction.
Friction between solids is called rolling or sliding friction.
The resistance that preclude actual motion is termed as static friction.
That which exists during motion is called dynamic friction.
(Orthodontic interest)