Biomechanics: 11 + 12, 13

material mechanics of biomechanics is interested in _________ ____________ of forces and moments

internal effects

tissue mechanics is the mechanics of

human connective tissue

how an object responds to load is determined by:

• magnitude

• duration

• direction

• location

• frequency

• rate

• variability

2 types of axial loading

• compression

• tension

2 kinds of bending

• 3 point

• 4 point

2 kinds of shear

• direct

• torsion

effect of bending on body/object is determined by 3 factors

• CSA

• distribution of material around neutral axis

• length of body (longer = problem)

area moment of inertia is the measure of

bodies resistence to bending

area moment of inertia is combined effects of

• CSA + how its distributed from neutral axis

loading causes two surfaces to move in opposite parallel direction

shear

rotational type of loading that exists when there is a twist around neutral axis

torsion

mechanical properties

• strength

• deformation

• stiffness

• toughness

  • ductile

  • brittle

ratio of change in load to change in deformation

stiffness

change in deformation to change in load

compliance

compliance is the opposite of

stiffness

amount of energy absorbed by body before failure

toughness

way a force is distributed within body

stress

• change in dimension normalized to original dimension

• analogous to stiffness

strain

property of material that exhibit both viscous + elastic characteristics when deforming

viscoelasticity

t/f: most human tissue demonstrates viscoelastic properites

true

properties of viscoelastic materials

• stress relaxation

• creep

• hysteresis

• strain rate dependency

_________ ___________ occurs when strain is held constant and stress decreases over time

stress relaxation

__________ occurs when stress is held constant and strain increases over time

creep

____________ is the loss of energy to heat when unloading after loading

hysteresis

hysteresis is also known as

cyclical loading

T/F: energy that is dissipated as heat cant be recouped

T

Strain Rate dependency

when mechanical properties are dependent on rate of change of strain

strain rate dependency refers to

how quickly is strain changing over time

Strength, stiffness, and toughness of viscoelastic material

• increases w increasing strain rate

severity of injury depends on

how much actual stress exceeds failure tolerance

actual stress

how much stress body is subjected to

margin of safety

difference between failure tolerance + actual stress

what happens when load is applied at the right frequency (not low or high)

improve tissue ability to handle stress

what happens if frequency load is too high

• tissue fatigues

• failure tolerance decreases

• margin of safety declines

wear occurs when

surface material is deformed & removed by frictional forces

__________ wear occurs when 2 surfaces are in contact

interfacial

___________ wear is the result of repetitive microdamage

fatigue

to increase margin of safety

• decrease load

• increase failure tolerance

to decrease imposed stress

• decrease load

• increase contact area

by increasing contact surface (CSA under strain)

• greatly decrease injury risk

___________ bone is compact bone

cortical

___________ bone is spongy bone

trabecular bone

bone is ______________; behavior determined by direction of forces

anisotropic

the shape of bone makes them susceptible to

bending

when do acute fractures occur

instantaneously

when do stress fractures occur

over time

bone is ___________ tissue; constantly undergoing modeling + remodeling

dynamic

modeling of bone

laying down new bone

remodeling of bone

absorbing old bone and laying down new bone

____________ loading is the signal to start modeling and remodeling

mechanical

if frequency of loading is too high, signals for resorption ________- those for reformation and decreases margin of safety

outpace

osteoporosis

severe loss of bone mineral density

3 types of cartilage are

• articular

• elastic

• fibrocartilage

__________ cartilage

• covers articular surfaces of bone

• loaded under compression

• distributes load across joints

• allows for movement

articular cartilage

fibrocartilage has a specialized role of

cushioning

elastic cartilage is found in

• external ear

• nose

what 2 things form the solid part of cartilage

• collagen

• proteoglycans

fluid part of cartilage

• interstital fluids w inorganic salts

fluid flows through _____________ __________ to support load

cartilage matrix

cartilage has a _______ ___________ property

self lubricating

with osteoarthritis ____________ cartilage and _____________ bone degenerate

articular cartilage and subchondral bone

with osteoarthritis, cartilage thickness _____________

decreases

Moderate intensity loading of cartilage is

positive

moderate intensity loading of cartilage causes

• increased proteoglycan

• decreased proteoglycan extractability

• increased cartilage thickness

repetitive high intensity loading of cartilageis negative and causes

• decreased collagen network

• site specific proteoglycan loss

• reduced cartilage stiffness

ligaments provide support to

keep joints intact

ligaments contain __________ ____ collagen

type 1

type 1 collagen of ligaments is arranged in ________ not parallel

bundles

tendons have a higher _________ than ligaments

collagen

the collagen in tendons are more _________ than in ligaments

organized

ligaments sustain __________ loads in 1 direction

tensile

ligaments are already ___________ w tension at rest

straightened

the _________ ___________ __________ regulates movement

muscle tendon complex

which end of MTC moves depends on the

amount of resistance at each segment muscle attaches

Primary structural component of tendons is _____ _____ _______ arranged parallel like muscle fibers

also type 1 collagen

T/F: type 1 collagen of muscle fibers is wavy at rest unlike tendons which is straightened

true

T/F:a stiffer tendon can produce more passive force

True

factors of MTC force-producing ability

• CSA

• MTC strength

• velocity

• type of action

• fiber type

MTC length: Ascending Curve

actin + myosin too close

MTC length: Plateau

actin + myosin optimal

MTC Length: Descending Limb

Actin + myosin too far apart

Force production

eccentric> isometric>concentric

during eccentric actions, muscle is acting __________

isometrically

During eccentric actions, tendon acts __________

eccentrically

the __________ force of tendon and __________ force of muscle increases total force production

passive force of tendon

active force of muscle

T/F: longer muscle fiber causes more force

True

Type 1 fibers are better for __________ and slow actions

isometric and slow actions

type 2 fibers: better for _________ powerful movements

faster

Human balance is the

ability to maintain equillibrium in gravitational field

the visual system provides info about

body position relative to moving environment

visual system is most sensitive to ________ frequency stimuli and requires ________ ___________ for integrating movement

• lower frequency

• more processing

______ system maintains upright body position

vestibular system

what system has the slowest processing of all afferent systems

vestibular

the vestibular system acts as ____________ w conflicting inputs

reference

Components of vestibular system for linear motion

utricle and saccule

Components of vestibular system for angular motion

semicircular canals

2 fluid filled sacs form part of labrynth of inner ear

• utricle and saccule

• electromechanical transducing receptor

macula contains

hair cells