Biomechanics lec 3
Foundation of human movement
Review of last lecture
Stress-strain curve –bone is special material
Elastic | yield point->plastic | failure
Function of skeleton Leverag
Support
Protection
Storage
Blood cell formation
Wolfs law
Resorption
Response to decreased stress
Osteoclasts dominate Disuse, immobilization, microgravity
Anisotropic properties Compression Tension
Sheer
Visoelastic properties
Load |_ c(fracture)C(fracture) Deformation
Apply stress faster the curve is steeper
Faster hit vs slower hit
More tension allowed before break vs more overall stress
Joint stability Ligaments Gravity Vacuum
Which joints are typically most stable

Muscular system
Characteristics of muscle
Irritability
Ability to respond to stimulation
Contractibility
Ability to shorten when it receives sufficient stimulation Can only contract by itself Unique to muscle tissue
Extensibility
Ability to stretch/lengthen beyond resting length Like rubber band, when let go the muscle will return to resting properties Protective mechanism
Elasticity
Ability to return to resting length after being stretched Oritection mechanism
Functions of muscle
Produce movement
Maintain posture ans positions
Stabilize joints
Other functions Support and protection visceral organs Alter and control cavity pressure maintain fiber type
Type I Slow twitch, oxidative Red, high myoglobin content
Endurance athletes, marathon runners/cyclists
Type IIa intermediate fast twitch, oxidative glycolytic
Type IIb Fast twitch, glycolytic White sprinters, jumper individual muscle organization motor unit page 13 group of muscle fib innervated by same motor neuron from 4-2,000 musc fiber per motor unit action potential signal to contract from mot neur neuromusculat junction also called end plate where action pot from neur meets muscle fib conduction velocity velocity at which action pot is propagated along memb resting potention sliding filament theory
a.f. huxley seeks to explain production of tension in muscle myosin and actin creat cross bridge muscle attachmen page 21 direct, tendon, aponeurosis characteristics of a tendon transmits muscle force to associated bone can withstand high tensile loads viscoelastic stress-strain response myotendinous junction where tendon and muscle join mechanical model of muscle
A.V. Hill
Three component model Contraction (CC)
Converts stimulation into force
Parallel elastic (PEC) Allows the muscle to be stretched Associated with fascia surrounding muscle
Series elastic (SEC)

Muscle role vs. angle of attachment
Page 26
Role of muscle
Prime mover Muscle prim response for a given movement
Assis mover Other musc cont to move
Agonist
Muscle creat same joint move
Antagonist
Muscle oppositng join movement
Stabilizer
Holds one segment still so a specific movement in an adjacent segment can occur
Neutralizer
Muscle working to eliminate undesired join movement of another muscle

Net muscle actions Isometric
Tension prod without vis change in join angle Holding arms to side Concentric Muscle visibly shortens while prod tension Up phase of a sit-up Eccentric Muscle visibly lengthens while producing tension Lowering phase of squat
- Factors influencing muscle force o Angle of attachment o Force time charact
 Force inc nonlinearly due to elastic component o Lenth tension relat o Force velocity relat
- Muscle fatigue o Fatigue results from:
 Peripheral (musc) mechanisms
 Central (nervous) mechanism o When motor unit fatigues:
 Change in frequency content
 Change in amplitude of emg signal o Sufficient rest restored initial signal content and amplitude

Strengthening muscle
Page 36

Biomechanics lecture 6
Injury potential
85% gen pop of west world lower back problem

` Effects of aging
Flex decrease
Trunk muscle lose app 1% of