Mechanical Behavior of tissues (bone/articular cartilage/tendon/ligament) Flashcards
(120 cards)
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
elastic materials
- 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
visco-elastic materials
- 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
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CREEP
- 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
stress-relaxation
- 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)
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cyclical loading
- 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
hysteresis
- 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
load (tension/stress)/Elongation(length/strain) graph
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
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viscoelastic behavior
- increased stiffness with increased strain RATE (faster=stiffer tissue)
- stress relaxation and creep deformation as per other tissues
- increase rate, going to tear
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creep vs stress relaxation
-constant load vs constant strain
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tendon loading
- 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
investing DCT
- paratenon: outside sheath of tendon
- epitenon: synovial tissue only in high friction locatoins
- endotenon: continuous with perimysium(outside muscle) and periosteum(sharpeys fibers)
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sharpeys fibers
come down into bone-cement tendon into bone
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functional implications
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
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injury and repair in tendons
- cellular reaction: inflammatory phase (days)
- collagen synthesis: proliferation (7days-7weeks)
- remodeling: maturation(7weeks-months)
- cross links form over time
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immobilization effects on tendon repair
- 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
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post injury immobilization vs early mobilization
- 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
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early intermittent passive mobilization in canine tendon
- ultimate load (strength/stress) increased with immediate mobilization
- reduction in adhesions (scar tissue)
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functions of myotendinous junction
- adhesion
- force transmission (muscle, tendon, bone)
- force must not exceed strength of interface(myotendinous junction) and adhesion
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muscle tendon and bone-ligament-bone failure under tension
- 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
4 variables to consider when prescribing exercise
1. mode (type of exercise)
2. intensity(load and pt feeling)
3. frequency(how long)
4. duration (number times per week)
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therapeutic effect of loading on per-articular DCT length
- 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
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therapeutic effect of loading on muscle length
- 30 second duration minimum to elongate muscle
- continuous duration
- once daily, 5 days a week
- heat up tissue will help stretch
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tissue training: strength
3-5 sets of 8-10 reps
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tissue training: endurance
3-5 set of 20-30 reps
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tissue training: endurance
3-5 sets of 30-40 reps
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tissue training: ligament
1000s of reps (timed)
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tissue training: cartilage
- hours of reps
| - 30-40 minutes of multiple modes, 5-7 minutes per exercise
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some of articular cartilage's clinically relevant gross structural/physiological features
- 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
what is articular cartilage made of?
- superficial=sheer resistant
| - deep=shock absorber/compression resistance
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tide mark
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
chondrocytes
- 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
what is the most unique AC material property as it relates to its mechanical behavior
- 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
how would you describe AC's visco-elastic mechanical behavior
- 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
mechanical behavior: permeability
- 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
structural macromolecules
-aging: decreased aggregation, decreased GAG content and shorter chains. structural modifications may be linked to changes in chondrocyte synthetic function
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biphasic creep response in compression
- 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
biphasic stress-relaxation response in AC
- 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
joint lubrication
- often under speculation
| - engineering based models attempt to apply it to body, not perfect system
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AC lubrication systems
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
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boundary lubrication
- lubricin prevents surface to surface contact
| - most important under low loads, at low speeds and long duraction (standing)
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fluid
4 types
1. hydrostatic
2. hydrodynamic
3. squeeze film
4. elastohydrodynamic
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hydrostatic
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
hydrodynamic
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
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squeeze-film
- 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
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elastohydrodynamic
- 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
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aberrant lubrication systems
- 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
theoretical mixed mode model during gait
- heel contact: squeeze film predominates
- stance phase: combo of boundary and fluid film
- swing: hydrodynamic predominates
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loss of PG matrix
- 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
development of osteoarthritis
- 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
tissue degeneration in chondromalacia
-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
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continuous passive motion
- increase blood flow
- promotes lubrication
- cycles fluid in and out to nutrient it
- prevents contactures
- stimulate mechanoreceptors to inhibit nociceptors
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controlled weight bearing
- 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
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aggressive exervise
- 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
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what intervention/tactics should we use to facilitate ac growth
1. 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
2. duration and/or frequency
- high repetition (100s-1000s) cyclical loading
- 5-7 minutes per exercise, functional exercise
- closed chain
3. mode: attempt to mimic function loading characteristics
- may consider minimizing combinations of shear and compressive
79
what makes bone a good material to serve as a mechanical lever?
intercellular calcified bone matrix:
- inorganic matter (mineral)
- 60-70% bone dry weight
- water(5-8%)
- organic matter(22-35%)
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extracellular organic matter
1. 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
2. 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
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intercellular bone matrix
- 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
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what makes bone such a dynamic tissue
1. bone cells
- osteocyte: mature cells
- osteoblasts: young cells, growth of bone
- osteoclasts: break down bone
2. existing bone structure: balance of ongoing bone deposition and bone tissue resorption
- growth: deposition
- aging: resorption
- disuse:resorption
- healing: balance
- exercise: blastic
83
wolffs law
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
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biomechanical properties of bone
- 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
bone demonstrates anisotropic mechanical behavior
- 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
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stress
force per unit area applied to a structure
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strain
deformation (change in shape) of a structure produced by an applied force/stress
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stress strain bone
- 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
compression
- 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
piezo-electric effects of bending forces
- (-) 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
effect of muscle contractions on bone
- 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
constant vs intermittent loading
- constant compressive loading produces increase in endosteal diameter and increase in intracortical porosity
- not good for long bones
- intermittant loading produces increased bone mass
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torsion loading
- 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
bone geometry: mechanical property
- 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
what intervention tactics/parameters should we use to facilitate growth
1. intensity:
- loading within tissue structural tolerance
- move carefully into the plastic zone
- pain free loading
2. duration and/or frequency
- many repetitions-cyclical loading: 100-1000s of reps, time based
3. mode: attempt to mimic functional loading characteristics
96
muscle mechanics
s
97
strength depends on..
- 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
fiber type
-each skeletal muscle in the human body contains type I, IIa, and IIb fibers
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type I
- slow twitch oxidative
- characteristics: small diameter, red in color, dense in capilaries, speed of contraction is slow, rate of fatigue is slow (soleus)
100
type IIA
- fast twitch oxidative glycolytic
- characteristics: as in type I except-intermediate diameter, fast speed of contraction, and intermediate rate of fatigue
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type IIb
- 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
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muscle in cross section
- epimysium surrounds the whole muscle
- perimysium surrounds the fascicules
- endomysium surrounds the individual muscle cells
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contractile element
- CE
| - contractile proteins
104
parallel elastic elements
- PEC
| - peri, epi, and endomysium (fascia)
105
series elastic elements
- SEC
| - tendons
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can mysiums generate force
-yes, just not sympathetically. indirectly generate force through muscle contraction
107
isometric contraction
- contractile element shortens and the series elastic element lengthens
- PEC go on slack
- ex=contract bicep with arm flexed to 90
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muscle twich
- 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
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torque
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
active insufficiency
- 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
passive insufficiency
- 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)
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torque
- 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)
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changes with aging
- 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
muscle force generation (isolated muscle studies)
- 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
muscle force varies with velocity of the contraction (clinical perspective)
- 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
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muscle force varies with the velocity of the contraction
-as the velocity of muscle contraction decreases and ultimately becomes "negative", tension produced by the muscle increases
-
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muscle force varies with type of contraction
- 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
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torque
strength
| -force x moment arm
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force dependent on
- cross sectional area
- fiber type
- length-tension
- velocity of contraction
- elastic components
120
moment arm dependent on
- deflection of tendon by bone or bony prominence
- changes with joint angle
- changes with person's size
