Chapter 3

Random Interesting Fun FactsMichael Jordan makes more money from Nike

annually than all of the Nike factory workers in Malaysia combined.

Right-handed people live, on average, nine years longer than left-handed people do.

It’s physically impossible for you to lick your elbow.

OverviewWhat is biomechanics?Levers & their classificationFactors impacting force production of leversLaws of motion and their influence on sport

movementEquilibrium, balance, & stabilityFactors influencing balance

What is Biomechanics?Bio= life; Mechanics= physical actionsStatics: form of mechanics that analyzes

systems in constant state of motionCould be no movement at allCould be constant velocity with no acceleration

Dynamics: form of mechanics that analyzes systems in motion and accelerating

What could a biomechanist do to improve sport performance?

Technique analysisIncrease speedIncrease strengthIncrease power

Minimize risk of injury (primarily overuse)

What does biomechanics have to do with anatomical kinesiology?

Anatomical kinesiology is the whatMuscle origins, insertions, and actions

Biomechanics is the howMechanical principles that dictate the

manner those muscles work

LeversWhat do levers have to do with human

movement?EVERYTHING!

Levers are rigid bars (in the body, bones) that move around an axis of rotation (a joint) or fulcrum

Forces (supplied by muscles) cause the movement to occur

Lever FunctionsMagnify a force

A simple crow barIncrease speed and range-of-motion (ROM)

Small amount of muscular contraction proximally can produce lots of movement distally

Lever FunctionsBalance torques

A triple beam scaleChange direction of force

A seesaw or a pulley of a weight machine

Lever TypesFirst, second, and third classArrangement of the applied force, the

fulcrum, and the resistance determines the classification

Classification determines the lever’s strengths and weaknesses

First ClassFARWhen axis close to force, produces

speed and ROM, when close to resistance, produces power

About 25% of the muscles in your body operate as first class levers

Force

Axis

Resist.

Axis

FR

RF

Axis

Axis

Force

Resist.

Example: Neck Example: Neck extensionextension

Second ClassARFVery few occurrences in the bodyGain resultant force (you can lift more), lose

distance

Force

Force

Resist. Axis

Third ClassRFAAs much as 85% of the muscles in the body

function as third class leversUsually produce speed at the expense of

forceGreater lever length = greater speed (ex.)

Force

Factors Impacting Force ProductionTorque: turning effect of an eccentric force

T= Applied Force * Force Arm Force arm is the perpendicular distance between

the applied force and the axis of rotationEccentric force: applied in a direction not in

line with center of rotation of non-moving axis

Factors Impacting Force ProductionResistance arm: distance between axis and

point of resistance (NOT the perpendicular distance)

Inverse relationship between force and force arm

Inverse relationship between resistance and resistance arm

Force components and resistance components proportionalF * FA = R * RA

Factors Impacting Force ProductionAngle of pull

Rotary component, dislocating component, and stabilizing component

When line of force (inserting tendon) is perpendicular to the bone it is inserting on (90 deg.), dislocating and stabilizing components = 0, therefore all force is rotary

Laws of MotionInertiaAccelerationReaction

Law of Inertia (Newton’s First Law)“A body in motion tends to stay in motion at

the same speed in a straight line unless acted upon by a force; A body at rest tends to remain at rest unless acted upon by a force”

English translation: unbalanced forces cause motion; Balanced forces don’t change anything

Law of Inertia (Newton’s First Law)

Mass is the measure of inertiaGreater mass = greater inertia

Implications for sport movementDecreased mass USUALLY

means you are easier to move (less inertia)

Agonist/antagonist reciprocal inhibition

Law of Acceleration(Newton’s Second Law)“The acceleration of an object is directly

proportional to the force causing it, is in the same direction as the force, and is inversely proportional to the mass of the object”

F = ma

Law of Acceleration(Newton’s Second Law)Impulse

Ft = m(vf-vi)Without time, it is impossible to generate force

and change velocityMomentum

Ft = (mvf-mvi)If masses are different, deficiencies can be

compensated for by increasing speed

Law of Acceleration(Newton’s Second Law)Implications for sport movement

Club/racket/bat weightFollow throughAthlete body weight

Law of Reaction(Newton’s Third Law)

“For every action there is an equal and opposite reaction”

Ground reaction forceImplications for sport

movementArtificial turf

Equilibrium, Balance, & Stability

Equilibrium is the state of zero acceleration (static or dynamic)

Balance is the ability to control equilibrium

Stability is a resistance to the disturbance of equilibrium

Factors Influencing Balance1. Location of the center of gravity in relation

to the base of support2. Size of the base of support3. Mass of the person4. Height of the center of gravity5. Traction/friction6. Sensory perceptions