Chapter 3

Random Interesting Fun Facts Michael 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.

Overview What is biomechanics? Levers & their classification Factors impacting force production of levers Laws of motion and their influence on sport movement Equilibrium, balance, & stability Factors influencing balance

What is Biomechanics? Bio= life; Mechanics= physical actions Statics: form of mechanics that analyzes systems in constant state of motion Could be no movement at all Could 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 analysis Increase speed Increase strength Increase power Minimize risk of injury (primarily overuse)

What does biomechanics have to do with anatomical kinesiology? Anatomical kinesiology is the what Muscle origins, insertions, and actions Biomechanics is the how Mechanical principles that dictate the manner those muscles work

Levers What 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 Functions Magnify a force A simple crow bar Increase speed and range-of-motion (ROM) Small amount of muscular contraction proximally can produce lots of movement distally

Lever Functions Balance torques A triple beam scale Change direction of force A seesaw or a pulley of a weight machine

Lever Types First, second, and third class Arrangement of the applied force, the fulcrum, and the resistance determines the classification Classification determines the lever’s strengths and weaknesses

First Class FAR When 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 F R R F

Force Resist. Example: Neck extension

Second Class ARF Very few occurrences in the body Gain resultant force (you can lift more), lose distance Force

Resist. Axis

Third Class RFA As much as 85% of the muscles in the body function as third class levers Usually produce speed at the expense of force Greater lever length = greater speed (ex.) Force

Factors Impacting Force Production Torque: 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 rotation Eccentric force: applied in a direction not in line with center of rotation of non-moving axis

Factors Impacting Force Production Resistance 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 proportional F * FA = R * RA

Factors Impacting Force Production Angle 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 Motion Inertia Acceleration Reaction

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 inertia Greater mass = greater inertia Implications for sport movement Decreased 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(v f -v i ) Without time, it is impossible to generate force and change velocity Momentum Ft = (mv f -mv i ) 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 weight Follow through Athlete body weight

Law of Reaction (Newton’s Third Law) “For every action there is an equal and opposite reaction” Ground reaction force Implications for sport movement Artificial 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 Balance 1. Location of the center of gravity in relation to the base of support 2. Size of the base of support 3. Mass of the person 4. Height of the center of gravity 5. Traction/friction 6. Sensory perceptions