Midterm 2

Question 1

tensile stress (Pa)

Answer 1

axial stress that tends to pull apart the molecules at the analysis plane
- object elongates

Question 2

compressive stress (Pa)

Answer 2

axial stress that tends to push or squash the molecules together at the analysis plane
- object shortens

Question 3

shear stress (Pa)

Answer 3

transverse stress that acts parallel to the analysis plane
- molecules slide past one another
- one force pushes down the other pushes up

Question 4

simple (uniaxial) loads

Answer 4

one type of stress produced, uniform across plane

Question 5

complex mechanical loads

Answer 5

multiple types of stress produced, stress varies across the plane

Question 6

bending (Pa)

Answer 6

counteracting tensile and compressive stress
- object with greater depth and larger CSA can withstand greater bending

Question 7

torsion (Pa)

Answer 7

twisting forces - shear force
- creates an internal torque
- object with greater diameter (area) can withstand greater torsion

Question 8

combined loads

Answer 8

combination of loads
1. muscles, tendons & ligaments: carry one type of load (uniaxial tension)
2. bones and cartilage: carry multiple loads (more complex)

Question 8

linear strain

Answer 8

change in length/deformation as a result of tensile or compressive stress

Question 9

shear strain

Answer 9

change in orientation of adjacent molecules as a result of molecules slipping past each other due to shear stress

Question 10

elastic modulus

Answer 10

ratio of stress to strain

Question 11

elastic behaviour

Answer 11

occurs when an object stretches under tensile load, but return back to original shape when the load is removed (rubber band)

Question 12

material strength

Answer 12

maximum stress/strain a material is able to withstand before failure

Question 12

plastic behaviour

Answer 12

when a permanent deformation of the object occurs under a load

Question 13

yield point

Answer 13

point on stress-strain curve where further stress will cause permanent deformation

Question 14

yield strength

Answer 14

stress at the elastic limit of a materials stress-strain curve

Question 15

ultimate strength

Answer 15

maximum stress the material is capable of withstanding

Question 16

failure strength

Answer 16

stress where failure actually occurs (endpoint, breakage)

Question 17

ductile vs brittle materials

Answer 17

ductile: can withstand lots of plastic deformation before failure = high failure strain
brittle: require little plastic deformation before failure = small failure strains

Question 18

hard vs soft material

Answer 18

hard: stiff = large failure stress
soft: pliant = small failure stress

Question 19

toughness

Answer 19

ability to absorb energy - area under stress-strain curve
- tougher = the more energy requires to reach failure

Question 20

viscoelastic materials

Answer 20

both viscous and elastic behaviours
(liquid and solid)
ex. bone, tendon, ligament, cartilage, muscle

Question 21

properties of viscoelastic materials

Answer 21

1. strain-rate dependency
2. stress-relaxation
3. creep
4. hysteresis

Question 22

strain-rate dependency

Answer 22

rate at which you deform/strain a tissue will effect the stress it feels
- faster loading = more stress

Question 23

stress-relaxation

Answer 23

Decrease in stress under constant strain (length held constant)

Question 24

creep

Answer 24

Increase in plastic strain under constant stress (load held constant)

Question 25

hysteresis

Answer 25

the amount of energy absorbed during loading and unloading

Question 26

active element

Answer 26

muscle tissue

Question 27

passive element

Answer 27

connective tissue

Question 28

collagen

Answer 28

stiff, brittle, high tensile strength, unable to resist compression

Question 29

elastin

Answer 29

pliant (soft), extensible, ductile, high failure strain

Question 30

isotropic

Answer 30

same mechanical properties in every direction

Question 31

ansiotropic

Answer 31

have different mechanical properties depending on direction of the load ex. tendon is stronger if tensile load is aligned with tendon fibres rather than transverse

Question 32

two primary factors affecting mechanical properties of tissues

Answer 32

1. activity 2. age

Question 33

activity

Answer 33

1. strength of CT increases with use 2. stiffness may also increase ***inactivity = decrease in strength of tissues

Question 34

age

Answer 34

1. CT increases in stranght with age until 30 years old, then strength decreases 2. bone become brittle and less tough with increasing age 3. tendons and ligaments become less stiff

Question 35

bones

Answer 35

1. strongest in compression, weakest in shear 2. high tensile strength 3. strongest and stiffest material 4. ansiotropic

Question 36

cortical (compact) bone

Answer 36

found in dense and hard outer layers of bone

Question 37

cancellous (spongy/trabecular) bone

Answer 37

less dense, porous bone that is spongy in appearance and found deep to cortical bone

Question 38

cartilage

Answer 38

able to withstand compressive, tensile, and shear loads

Question 39

hyaline cartilage

Answer 39

covers the end of long bones at joints 1. no blood supply, thin to allow diffusion of nutrients 2. made of water and water is not compressible so under compressive load, collagen is under tension

Question 40

fibrous cartilage

Answer 40

found within some joint cavities

Question 41

elastic cartilage

Answer 41

found in external ear and in several other organs that are not part musculoskeletal system

Question 42

tendons and ligaments

Answer 42

major difference is arrangement of their collagen fibres

Question 43

tendons

Answer 43

collagen fibres are bound together in parallel - parallel arrangement produces a structure that is very stiff and high in tensile strength - little resistance to compression or shear

Question 44

ligaments

Answer 44

collagen fibres are bound together nearly parallel - have slightly larger elastin component making them less stiff and slightly weaker than tendons

Question 45

muscle fibres

Answer 45

encased in endomysium

Question 46

fascicles

Answer 46

bundles of muscle fibres - encased in perimysium

Question 47

whole muscle

Answer 47

bundles or muscles fascicles - epimysium

Question 48

tendon

Answer 48

woven CT that connects muscle to bone allowing for movement

Question 49

sarcomeres

Answer 49

basic contractile unit of a muscle - contain overlapping filaments of myosin (thick) and actin (thin)

Question 50

resting state

Answer 50

tropomyosin prevents myosin from bonding to actin

Question 51

z-line

Answer 51

band that anchors actin to each other, boundary of one sarcomere

Question 52

I-band

Answer 52

area that contains only actin

Question 53

A-band

Answer 53

area that contains myosin, overlapping with actin

Question 54

H-zone

Answer 54

area that contains only myosin

Question 55

M-line

Answer 55

band that anchors myosin to one another

Question 56

factors affecting force development

Answer 56

1. length 2. velocity 3. physiological cross-sectional area 4. muscle geometry 5. activation

Question 57

resting length

Answer 57

greatest active tension - optimal length

Question 58

contractile element

Answer 58

represents force development by sarcomeres

Question 59

force-velocity relationship

Answer 59

the greater the shortening velocity, the smaller the force produced - slower the contraction velocity = more force produced (more time for cross-bridges to form and exert force)

Question 60

concentric

Answer 60

muscle shortens while generation force (lifting weights) 1. muscle contraction or flexion - muscle is moving body part closer to center body 2. muscle tension exceeds the external load AS VELOCITY INCREASES, FORCE DECREASES

Question 61

eccentric

Answer 61

muscle lengthens while generating force (lowering weight or body) 1. lengthening or extension - muscle is moving body part away 2. external load exceeds muscle tension = muscle lengthens AS VELOCITY INCREASES, FORCE INCREASES

Question 62

physiological cross-sectional area

Answer 62

adding sarcomeres in parallel makes a muscle stronger

Question 63

activation of muscle fibres

Answer 63

force produced by a muscle is directly proportional to number of fibres that contract at any given time - more fibres contracting = more force produced

Question 64

fine/precise control

Answer 64

smaller number of muscle fibres per motor neuron

Question 65

coarse control

Answer 65

larger number of muscle fibres per motor neuron

Question 66

hennemans size principle

Answer 66

motor units are recruited from smallest (slow-twitch) to largest (fast-twitch) - beneficial for fatigue prevention + fine + coarse control

Question 67

sarcomere arrangement

Answer 67

length-wise= strong muscle height-wise= fast muscle ***longer the muscle length, the easier the ability to create tension

Question 68

shorter moment arm

Answer 68

more force required with same torque

Question 69

larger joint angle

Answer 69

faster the muscle

Question 70

longer moment arm

Answer 70

less force required with same torque

Question 71

smaller joint angle

Answer 71

slower the muscle

Question 72

series element

Answer 72

muscle fibres aligned end-to-end so the forces are additive 1. greater ROM 2. greater force production 3. limited strength ***typically longitudinal muscle

Question 73

parallel element

Answer 73

muscle fibres aligned side-by-side, running parallel to each other 1. greater strength (not faster) 2. limited ROM

Question 74

force-length relationship - optimal length

Answer 74

generate highest force due to best overlap of myosin and actin to form cross-bridges

Question 75

force-length relationship - too short

Answer 75

force production is reduced cause there is limited overlap between myosin and actin thereby reducing cross-bridge formation

Question 76

force-length relationship - too stretched

Answer 76

force production is reduced cause myosin and actin are pulled too far apart, limiting cross-bridge formation

Question 77

passive tension

Answer 77

as a muscle length increases (overstretch), active force is decreasing and passive force component comes into play and increases total force production of the muscle