Mechanical Behavior of tissues (bone/articular cartilage/tendon/ligament) Flashcards
1
Q
Connective Tissue: structure and mechanical properties
A
s
2
Q
structure of connective tissue
A
- characterized by a wide dispersion of cells in the presence of a large extracellular matrix (ECM)
- microscopic level
- -interfribrillar (ground substance/collagen) and fibrillar (fibrous) components
- CT are unique among body structures. function determined by ECM unlike muscle/nerve where cell behavior dictates function
3
Q
fibroblast
A
basic cell of most connective tissue
- may become:
- chondroblast: cartilage
- osteoblast: bone
- tenoblast: tendon
4
Q
extracellular matrix
A
- interfibrillar (ground substance)
- -hydrated proteins:
- -PGs
- -glycoproteins
- fibrillar (fibrous compenent)
5
Q
PGS
A
proteoglycans
-attached are one or more polysaccaride chains called glycosaminoglycans (GAGs) (chondroitin and chondroitin sulfate, hyaluronon)
6
Q
glycoproteins
A
-compound containing a carbohydrate (sugar type molecule) covalently linked to protein
7
Q
Pgs and gags
A
- proportion of PG’s in extracellular matrix effects hydration
- GAGs are negatively charged such that a concentration of negatively charged PG’s creates a swelling pressure=water flows into the extracellular matrix
- collagen fibers resist and contain the swelling (via tensile stress w/osmotic swelling pressure)=creates regidity of matrix, therefore, can resist compressive forces
- tissues subjected to high compression forces have a high PG content and those that resist tensile loads have a low content
- GAGs have affinity for H2O, tension load increased on collagen fibers, creates rigidity
- PGs found in all connective tissues
8
Q
types of connective tissue
A
blood
bone
cartilage
connective tissue proper (tendons and ligaments)
9
Q
fibrillar component
A
2 major components: collagen and elastin
- collagen: main substance of most connective tissues
- -most abundant protein in body
- -tensile strength similar to steel, resistance to tensile forces
- elastin: uncoils into a more extended formation when the fiber is stretched and recoils psontaneously when the stretching force is removed
- tissues that require more give contain more elastin
10
Q
collagen type I
A
-predominantly in ll, tendons, menisci, and joint capsules
11
Q
collagen type II
A
-predominantly in hyaline articular cartilage and nucleus pulposus of disk
12
Q
elastin
A
- properties allow the fibers to deform under force and return to original state (rubber band)
- generally elastin smaller in in proportion to collagen in connective tissues (varies greatly)
- ligamentum flavum has higher elastin
13
Q
composition and structure of connective tissue
A
- sparsely vascularized, “parallel” fibered (primarily type 1 collagen), dense connective tissue in tendon and ligament
- delayed healing
- structure and chemical composition of ligaments and tendons identical in humans and many other mammalian models
14
Q
composition and structure
A
- fibroblasts synthesize and secrete procollagen (pre-collagen) which is cleaved extracellularly to produce type I collagen
- each polypeptide chain is coiled in a left-handed helix. these three alpha chains are then coiled together in a right handed-helix. such structure increases molecular strength
15
Q
cross links
A
- formed by GAG’s between collagen molecules provide strength to fibrils
- cross links are few and fairly easily broken in new collagen, become strong with maturation
- aid resistance of tension loads
- orientations of collagen makes them good tension load resistors
16
Q
elastin content
A
- more in ligaments than tendons
- proportion of elastin important in determining mechanical properties
- tension loaded ligament=preloaded
- assists in ability to come back up
- may be why ligamentum flavum has more elasitin in it
17
Q
general mechanical principles
A
overload
- specificity
- reversibility
18
Q
overload
A
- tissues increase their structural or functional capability in response to overloading (stimulus and response)
- develop tissue=impart stimulus
19
Q
specificity
A
-specific stimulus for adaptation elicits specific structural and functional changes in specific elements of tissues
20
Q
reversibility
A
- discontinuing training stimulus will result in de-training and the adaptive changes regress (disuse atrophy)
- lose muscle benefit that you gained in 72 hours if not stimulated again
21
Q
SAID
A
Specific Adaptations to Induce Demands
22
Q
elasticity
A
-property of a material or structure to return to its original form following removal of deforming load (compression, tension, sheer)
23
Q
plasticity
A
- property of a material to deform permanently when its loaded beyond its plastic (compression resistance) range
- permanent change in density
24
Q
viscosity
A
- property of a material to resist loads that produce shear, controls fluid rate of flow
- higher viscosity=slower deformation/rate of flow
25
Q
elastic materials
A
- return to normal form/shape following removal of deforming load (solid property)
- energy is stored during loading and released completely during unloading-no energy loss (if in elastic region)
- loading-unloading curves are the same
- every tissue contains visco-elastic tissue
26
Q
visco-elastic materials
A
- a combination of viscosity and elasticity
- sensitive to rate of loading or deformation
- higher rate: greater energy stored cannot dissipate rapidly througha single crack, comminution of bone and extensive S.T. (soft tissue) damage occurs
- low rate: energy can dissipate through a crack, bone, and S.T. remain relatively intact. little displacement occurs
- faster-rate=more damage
- all connective tissues
- makes behavior time, rate, and history dependent
27
Q
CREEP
A
- load (stress) is applied and then held constant over time (not cyclic)
- continued deformation over time though load is held constant
- deformation=strain
- use to enhance ROM in tissues like ligaments and tendons that respond to longer period of time stretching
- force remains constant while length changes
- initial elastic deformation, continues to elongate over time (CREEP)
- constant force, increasing length
28
Q
stress-relaxation
A
- tissue stretched to a fixed length while the force required to maintain this length decreases over time
- length remains constant while force decreases
- less force is required to maintain same tissue length/stretch
- constant length, decreasing load (force) (naturally)
29
Q
cyclical loading
A
- causes a shift of curve to the right
- shift decreases in magnitude with each repetition
- repeated on and off force
- load=stress
- strain=elongation (deformation)
- demonstrating elasticity of tissues
- stretch=permanent plastic change
30
Q
hysteresis
A
- a load-deformation curve that reveals that the forces applied and removed do not follow the same path
- not all the energy gained as a result of the lengthening work is recovered during the exchange from energy to shortening work
- some energy is lost, usually as heat
- energy lost/deformation can be a good thing, CREEP and stress-relaxation are trying to create a hysteresis curve to permanently change tissues (stretch them)
31
Q
load (tension/stress)/Elongation(length/strain) graph
A
see stress strain curve
1: more elongation w/load
- “toe” region, straightening out of fibers
2. elastic zone-tissue releases to same place
3. yield point/stress(load)=point of no return. no longer elastic change, created hysteresis loop
4. rupture
32
Q
viscoelastic behavior
A
- increased stiffness with increased strain RATE (faster=stiffer tissue)
- stress relaxation and creep deformation as per other tissues
- increase rate, going to tear
33
Q
creep vs stress relaxation
A
-constant load vs constant strain
34
Q
tendon loading
A
- tendon loading differs from other connective tissues due to its direct attachment to skeletal muscles
- thus muscle contraction force and relative cross-sectional area of muscle to tendon must be considered
- though muscle forces may be very high, tendon tensile strength tends to be twice that of its muscle
- thus muscle ruptures more common than tendon rupture
- tendon loading is typically 5-10% of ultimate stress (typical day only imparts 5-10% of stress tendon can hold)
35
Q
investing DCT
A
- paratenon: outside sheath of tendon
- epitenon: synovial tissue only in high friction locatoins
- endotenon: continuous with perimysium(outside muscle) and periosteum(sharpeys fibers)
36
Q
sharpeys fibers
A
come down into bone-cement tendon into bone
37
Q
functional implications
A
Consequences of increased tissue stiffness in DCT surrounding muscle, peri-articular…:
- rapid, eccentric loading can be problematic especially achilles tendon of males 35-55
- posture: aging and sitting behaviours self-perpetuating
- ability to retain water decreases with age and increase stiffness with less water
- # 1 way pts strain their muscle is eccentrically
38
Q
injury and repair in tendons
A
- cellular reaction: inflammatory phase (days)
- collagen synthesis: proliferation (7days-7weeks)
- remodeling: maturation(7weeks-months)
- cross links form over time
39
Q
immobilization effects on tendon repair
A
- no movement for 9 weeks dimished load tolerance
- controlled immobilization is key, need to use some motion
- type of motion is important: stress/strain curve
40
Q
post injury immobilization vs early mobilization
A
- immobilization in tendon reduces water content, PG content and strength
- immobilization weakens bone-ligament-bone complex just after 8 weeks in ACL
- tendon softening in first 1-2 weeks pronounced with immobilization
41
Q
early intermittent passive mobilization in canine tendon
A
- ultimate load (strength/stress) increased with immediate mobilization
- reduction in adhesions (scar tissue)
42
Q
functions of myotendinous junction
A
- adhesion
- force transmission (muscle, tendon, bone)
- force must not exceed strength of interface(myotendinous junction) and adhesion
43
Q
muscle tendon and bone-ligament-bone failure under tension
A
- muscle-tendon injuries due to stretching or combined stretching and contraction tend to occur at myotendinous junction
- age dependent behavior:
- pre-epiphyseal closure-failure at epiphysis (growing years)
- post-epiphyseal closure-failure at MTJ
- clinically midsubstance tears of bone-ligament-bone are more common in adults than avulsion
44
Q
4 variables to consider when prescribing exercise
A
- mode (type of exercise)
- intensity(load and pt feeling)
- frequency(how long)
- duration (number times per week)
45
Q
therapeutic effect of loading on per-articular DCT length
A
- low load of minutes in duration
- mechanoreceptors inhibit nociceptors
- tendon, ligament, capsule all benefit from elongation
- 5-40 min
- non-thrust will not change length of a tissue
46
Q
therapeutic effect of loading on muscle length
A
- 30 second duration minimum to elongate muscle
- continuous duration
- once daily, 5 days a week
- heat up tissue will help stretch
47
Q
tissue training: strength
A
3-5 sets of 8-10 reps
48
Q
tissue training: endurance
A
3-5 set of 20-30 reps
49
Q
tissue training: endurance
A
3-5 sets of 30-40 reps
50
Q
tissue training: ligament
A
1000s of reps (timed)
51
Q
tissue training: cartilage
A
- hours of reps
- 30-40 minutes of multiple modes, 5-7 minutes per exercise
52
Q
some of articular cartilage’s clinically relevant gross structural/physiological features
A
- an avascular, aneural tissue with a low metabolic rate
- it is designed to withstand rigorous loading without failure to distribute loads and to provide a low friction surface
53
Q
what is articular cartilage made of?
A
- superficial=sheer resistant
- deep=shock absorber/compression resistance
54
Q
tide mark
A
demarcation between calcified layer with uncalcified layer
- loses superficial layer with age
- ossification of cartilage->wolfes law
- cancellous bone increases
- loses shock absorption
- bone is not aneural, pain with arthritis comes from bone on bone contact (subchondral bone)
55
Q
chondrocytes
A
- make and secrete matrix, inhibiting cell-cell contact
- matrix transmits mechanical signals to cell membranes
- these cells may act as transducers in that the mechanical stress elicits a cell response to change synthetic activity
56
Q
what is the most unique AC material property as it relates to its mechanical behavior
A
- fluid component
- key feature both structurally and mechanically in this hydraulic tissue
- water content decrease and PG content increases with increased depth of tissue
- deeper we go, smaller pores in cartilage, H2O has difficult time going through it
- solid component:
- porous, permeable matric primarily of type II collagen and PG
- extremely low permeability coefficient
- anisotropic tissue-will not resist forces in all directions (sheer hurts)
- heterogenous CT (solid and semi-solid materials)
- allows permeability for H2O in cartilage. compression forces force fluid out of cartilage like a sponge, but decreasing pore size slows down compression (viso-elastic)
57
Q
how would you describe AC’s visco-elastic mechanical behavior
A
- stress developed in collagen-PG solid matrix
- frictional drag generated by interstitial fluid flow through matrix
- greater PG aggregation=increased elastic response and rupture strength
- aging reduces degree of PG agregation
58
Q
mechanical behavior: permeability
A
- rate of creep is an indicator of tissue permeability (increased creep, decreased permeability)
- small pores result in low permeability and high friction to flow (increased creep)
- compression further reduces pore size
- mode=cyclic loading for cartilage (want that bottleneck, dont want to continously stress b/c pushes out fluid)
59
Q
structural macromolecules
A
-aging: decreased aggregation, decreased GAG content and shorter chains. structural modifications may be linked to changes in chondrocyte synthetic function
60
Q
biphasic creep response in compression
A
- rapid initial exudation of fluid from articular surface
- external compressive load creates creep which is resisted by stress developed in collagen-PG solid matrix and frictional drag
- continued slower exudation until deformation equilibrium reached
- external compressive load ultimately equals stress developed in collagen_PG solid matrix alone
- -4-16 hours of constant load to cessation of fluid flow (starts to hurt)
- older people have pain because of the increasing tide mark, less surface between bones and it takes less time to reach that equilibrium and pass it
61
Q
biphasic stress-relaxation response in AC
A
- stress is increased until a given deformation is reached and then deformation/strain maintained, stress decreases under constant strain until equilibrium is reached
- fluid redistribution is responsible for tissue stress relaxation
- rapid redistribution of load throughout tissue reduces peak stresses and thus contributes to articular cartilage’s resilience
- constant strain/deformation and the load required to create that decrease over time
- fibers more compliant internally
- CREEP is when you keep pushing (increasing stress) to further stretch
- 2 things cause equlibrium: fluid distribution and collagen fiber alignment
62
Q
joint lubrication
A
- often under speculation
- engineering based models attempt to apply it to body, not perfect system
63
Q
AC lubrication systems
A
2 types: boundary and fluid
- boundary: each load bearing surface is coated with lubricin (like poles of a magnet) (diarthrodial joints), two surfaces do not touch each other
- –most effective at low loads
- fluid: a film of fluid interposed between 2 joint surfaces
64
Q
boundary lubrication
A
- lubricin prevents surface to surface contact
- most important under low loads, at low speeds and long duraction (standing)
65
Q
fluid
A
4 types
- hydrostatic
- hydrodynamic
- squeeze film
- elastohydrodynamic
66
Q
hydrostatic
A
weeping
- film of lubrication that is maintained under pressure (weep out) of cartilage with pressure and returns with unloading
- -most effective under high loads but effective under most conditions (supplied by contraction of mm or compression in CKC-jumpiing, contract muscles)
- on/off loads
- non-parallel force
67
Q
hydrodynamic
A
wedge of fluid is created when non parallel opposing surfaces slide on one another-lifting pressure occurs in wedge of fluid and increases viscosity, keeps surfaces apart
- riding a bike at high speed decrease resistance will separate knee joint and lifting pressure
- pushing a wave of fluid
- lifting pressure, speed speaks to lift/separation retropatellar
68
Q
squeeze-film
A
- pressure created in fluid film by surfaces moving that are perpendicular to one another
- fluid is squeezed out as surfaces approximate=increased fluid viscosity with pressure
- -most beneficial for high loads maintained for a short duration
- orientation of force makes it different from hydrostatic lubrication
69
Q
elastohydrodynamic
A
- fluid film is maintained at a uniform thickness by elastic deformation of articular surfaces
- the cartilage deforms slightly to maintain adequate layer of fluid between surfaces
70
Q
aberrant lubrication systems
A
- adhesive wear: osteochondritis dessicans (drying out, no fluid in joint)
- -complete or incomplete separation of a portion of cartilage and bone
- abrasive wear: joint mouse irritation-loose body (rocks in a dryer)
- fatigue wear: PG washout, aging, DJD
71
Q
theoretical mixed mode model during gait
A
- heel contact: squeeze film predominates
- stance phase: combo of boundary and fluid film
- swing: hydrodynamic predominates
72
Q
loss of PG matrix
A
- caused by prolonged immobilization, some anti-inflammatory drugs, trauma/sx, infection and/or as a normal component of aging
- may be reversible dependent upon degree and duration
- NSAIDS can cause proteoglycan washout in tissues long term
73
Q
development of osteoarthritis
A
- early stages: fraying of collagen bundles in superficial layer
- often see rapid progression once fraying has begun due to fiber orientation within tissue
- superificial layer of cartilage is sheer force oriented, but as it wears and tears the lower levels cannot withstand sheer because of their orientation and they degrade faster
74
Q
tissue degeneration in chondromalacia
A
-softening of cartilage appears to begin in layers 3 and 4. thus early visualization of pathology is difficult
-negative effect of chondromalaysias (disuse) at layers 3-4
-DJD too much
Chondromalaysia: too little
75
Q
continuous passive motion
A
- increase blood flow
- promotes lubrication
- cycles fluid in and out to nutrient it
- prevents contactures
- stimulate mechanoreceptors to inhibit nociceptors
76
Q
controlled weight bearing
A
- rabbit knee joint cartilage grew faster and thicker in areas of WB vs NWB regions
- constant load is detrimental while intermittent loading may help healing via explants. vascular tissue necessary in transplantation process
77
Q
aggressive exervise
A
- treadmill exercise rats show greater degree of artic. cartuilage damage with aging than sedentary rats
- long distance running is detrimental to WB articualr cartilage in healthy beagles
78
Q
what intervention/tactics should we use to facilitate ac growth
A
- intensity: (load, quality, what they feel)
- pain as guide??-no pain should be present, just pressure
- edema or effusion as guide?-doing too much if present
- full body weight loading may be excessive
- less is more - duration and/or frequency
- high repetition (100s-1000s) cyclical loading
- 5-7 minutes per exercise, functional exercise
- closed chain - mode: attempt to mimic function loading characteristics
- may consider minimizing combinations of shear and compressive
79
Q
what makes bone a good material to serve as a mechanical lever?
A
intercellular calcified bone matrix:
- inorganic matter (mineral)
- 60-70% bone dry weight
- water(5-8%)
- organic matter(22-35%)
80
Q
extracellular organic matter
A
- type I collagen:
- organization varies with bone type
- -resist stretching and have little extensibility
- -accounts for 90% of ECM and 25-30% of dry weight - amorphous ground substance
- GAGs serve as cementing substance between osteons (bridges)
- associated with proteins primarily in form of PGs
- specific glycoproteins contain glutamic acid causing them to bind avidly to calcium
- each haversian system is a ring connected by GAGs
- allows bone to absorb stress and share it equally through bridges
81
Q
intercellular bone matrix
A
- inorganic matter: calsium and phosphorus abundant in form of hydroxyapatite crystals
- decalcified bone retains shape but is as flexible as tendon
- removal of organic matter in matrix leaves bone again with its original shape, but is fragile and brittle (osteoporosis)
- need both organic and inorganic together for strong bone
82
Q
what makes bone such a dynamic tissue
A
- bone cells
- osteocyte: mature cells
- osteoblasts: young cells, growth of bone
- osteoclasts: break down bone - existing bone structure: balance of ongoing bone deposition and bone tissue resorption
- growth: deposition
- aging: resorption
- disuse:resorption
- healing: balance
- exercise: blastic
83
Q
wolffs law
A
effective applied load decreased:
- bone deposition decreases: disuse atrophy
- immobilization
- -casting and NWB status: following 8 weeks of immobilization may see a 3 fold decrease in load to failure, stiffness and energy storing capacity
- -plates/screws implanted to reduce stress at fracture site may reduce/slow healing to normal strength. however, fixation site strength may increase
- bone needs to take up load after surgery, not plates
- just enough offloading to help healing, but not enough to prevent strength/load intolerance once removed
- micro-motion of screws may stimulate bone to lay down more bone
84
Q
biomechanical properties of bone
A
- cortical bone/compact bone is stiffer than cancellous bone: steeper slope of stress/strain curve (take a lot of load but will not deform well)
- cancellous bone porous structure=greater capacity for energy storage (spongy-gags)
- bone becomes more brittle with age
- bone is more brittle with increasing velocity of loading–time for bone to absorb force is needed
- -bone demonstrates anisotropic mechanical behavior (have to respond to forces put on them on a daily basis, bone behavior changes depending on load put on it)
85
Q
bone demonstrates anisotropic mechanical behavior
A
- strength is greatest in direction in which loading is most common
- strength decreases as direction of loading changes from:
- -compression-longitudinal tension-oblique tension-transverse loading
- -best served compression/tension
86
Q
stress
A
force per unit area applied to a structure
87
Q
strain
A
deformation (change in shape) of a structure produced by an applied force/stress
88
Q
stress strain bone
A
- cortical bone is stiffer than cancellous
- cortical bone can withstand greater stress but less strain than cancellous bone
- cancellous bone can sustain strains of 75% before failing
- cortical bone can sustain straing sof only 2% before failing
89
Q
compression
A
- structure shortens and widens-bone somewhat widens
- produces common fractures in vertebrae
- constant compression may hinder growth
- unequal loading may produce valgus/varus deformity
- cyclical loading of appropriate parameters may facilitate growth and repair
90
Q
piezo-electric effects of bending forces
A
- (-) charge on side of compression and (+) charge on side of tension
- osteoblasts tend to migrate toward (-) electrode; while osteoclasts tend to migrate toward (+) electrode
- bone deposition increases on side of compression
- standing on one leg loads femur, bends in outwardly (concave side is + charge)
91
Q
effect of muscle contractions on bone
A
- usually oppose antagonist or gravity to counterbalance bending (abductors resisting tension on superior femoral neck with WB-standing on one foot, abductors resist convexity of force)
- acting independently creates bending of bones
- create tension at tendon-bone junction
- create tuberosities/trochanters developmentally-develop as you apply force to that area of bone
- pathologically may create avulsion fractures
92
Q
constant vs intermittent loading
A
- constant compressive loading produces increase in endosteal diameter and increase in intracortical porosity
- not good for long bones
- intermittant loading produces increased bone mass
93
Q
torsion loading
A
- spiral fractures are common withthese forces
- epiphyseal plate is most sensitive to torsion forces
- under torsional load, newly forming bone will grow away from epiphysis in a spiral fashion
- -ie structural scoliosis, femoral or tibial torsion
94
Q
bone geometry: mechanical property
A
- cross sectional area: greater area=stiffer and stronger bone
- healing fracture begins with large callus
- screw holes to stabilize fracture sites initially weaken the bone to which they are attached. 8 weeks to return to normal strength due to remodeling
- same issue with removal of hardware (bridge of tension/compression needs to reheal)
95
Q
what intervention tactics/parameters should we use to facilitate growth
A
- intensity:
- loading within tissue structural tolerance
- move carefully into the plastic zone
- pain free loading - duration and/or frequency
- many repetitions-cyclical loading: 100-1000s of reps, time based - mode: attempt to mimic functional loading characteristics
96
Q
muscle mechanics
A
s
97
Q
strength depends on..
A
- depends on both: muscle force x moment arm (torque)
- mechanical factors: rotary component of muscle force and length of moment arm
- physiological factors: length of the muscle, velocity of contraction, fiber orientation, cross sectional area, and fiber type
- strength=ability to generate torque
98
Q
fiber type
A
-each skeletal muscle in the human body contains type I, IIa, and IIb fibers
99
Q
type I
A
- slow twitch oxidative
- characteristics: small diameter, red in color, dense in capilaries, speed of contraction is slow, rate of fatigue is slow (soleus)
100
Q
type IIA
A
- fast twitch oxidative glycolytic
- characteristics: as in type I except-intermediate diameter, fast speed of contraction, and intermediate rate of fatigue
101
Q
type IIb
A
- fast twitch glycolytic
- characteristics: large diameter, white in color, sparse capillarity, fast speed of contraction, and fast rate of fatigue
- muscles predominantly type II/fast twitch often called mobility, non-postural, phasic muscles
102
Q
muscle in cross section
A
- epimysium surrounds the whole muscle
- perimysium surrounds the fascicules
- endomysium surrounds the individual muscle cells
103
Q
contractile element
A
- CE
- contractile proteins
104
Q
parallel elastic elements
A
- PEC
- peri, epi, and endomysium (fascia)
105
Q
series elastic elements
A
- SEC
- tendons
106
Q
can mysiums generate force
A
-yes, just not sympathetically. indirectly generate force through muscle contraction
107
Q
isometric contraction
A
- contractile element shortens and the series elastic element lengthens
- PEC go on slack
- ex=contract bicep with arm flexed to 90
108
Q
muscle twich
A
- passively pulling on the muscle beyond rest length will stretch the PEC and they will also contribute to the tension
- muscle contraction creaetes tension
- optimal length tension=mid position of a joint
- add sarcomeres to lengthened muscle
- mysiums generate force to resist muscles lengthening further
109
Q
torque
A
muscle force x moment arm
- muscle force will vary with muscle length in accordance with the length tension curve
- too short or too long will not produce optimal force
110
Q
active insufficiency
A
- agonist muscle is too short to produce effective tension and thus no further ROM can be actively achieved
- typically bi or multi-articulate muscles
- long head biceps vs long head triceps
- rectus femoris vs hamstring
- triceps is elbow extender and GH extentendor
- LH biceps is elbow flexor and GH flexor
111
Q
passive insufficiency
A
- antagonist muscle is on stretch and is too short (too far elongated) to allow further passive range of motion
- typically bi or milti-articulate muscles
- can be either actively insufficient of biceps or passively insufficient in triceps for elbow flexion (tests to determine)
112
Q
torque
A
- muscle force x moment arm
- muscle force varies with cross sectional area of the muscle
- fiber arrangement is a key issue in determining total cross sectional area
- greater cross sectional area=greater force output
- larger cross sectional area means there is more to contract (biceps vs. pecs major)
113
Q
changes with aging
A
- cross sectional area increases years 0-20s then decreases to a lesser degree 30s+
- thus maximal strength 20s-30
- at age 65, have about 85% of muscle strength they had at age 20
- loss is reversible +/or can be minimized
- loss of strength more in legs than arms
- males stronger than females
114
Q
muscle force generation (isolated muscle studies)
A
- velocity of muscle contraction is a function of the load being lifted
- speed of shortening of the myofilaments is the rate at which the myofilaments are able to slide past one another and form/re-form cross bridges
- speed is related to fiber type and length
115
Q
muscle force varies with velocity of the contraction (clinical perspective)
A
- force generated is a function of the velocity of muscle contraction
- max shortening speed occurs when there is no resistance to shortening, however, no tension is developed in the muscle b/c there is no resistance
- concentrics: as shortening speed decreases, tension increases
- isometrics: speed is zero, therefore, greater tension generated compared to concentrics
- eccentrics: as speed of lengthening increases, tension increases (trying to slow down muscle harder to prevent tear against fast speed)
- isometrically generate a force greater than concentrically, so when doing isometric exercises you really want to be doing sub-isometrics because there is a greater load, and the muscle will probably be healing still
116
Q
muscle force varies with the velocity of the contraction
A
117
Q
muscle force varies with type of contraction
A
- isometric: great strengthening but only at that joint angle +/-10 degrees
- concentric: dynamic, but velocity-tension relationship often limits strengthening at higher (more functional) velocities
- eccentric: great strengthening, possible tissue damage (micro tears) due to potential for large muscle force production
- isotonic: dynamic contractions, but intensity limited by capability in weakest part of ROM (typically end ranges)(umbrella term for isometric, concentric, and eccentric contractions)
- isokinetic: good strengthening throughout the range of motion. functional?
- any and all types can be prescribed, depends on pt
118
Q
torque
A
strength
-force x moment arm
119
Q
force dependent on
A
- cross sectional area
- fiber type
- length-tension
- velocity of contraction
- elastic components
120
Q
moment arm dependent on
A
- deflection of tendon by bone or bony prominence
- changes with joint angle
- changes with person’s size
