- extensibility - elasticity - contractility

muscle mechanics Flashcards by Chelsea Schuaman

purpose of muscles

3 of them

enable boens to move at joints
provide strength and protection to skeleton
absorb shock and distribut loads

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muscles properties

extensibility
elasticity
contractility

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connective tissue surrounding muscle fiber

epimysium: covers muscles
perimysium: covers fasicles
endomysium: covers fibers

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structures within muscle fiber

sarcolemma: muscles cell membrane
myofibril
sarcomere

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structures within a sarcomere

actin

- myosin myofilaments

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6 things affecting muscles funtion

muscles actions
joint structure
muscles structure
contraction type
muscles mechanics
neuromuscular

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factors affecting muscle force production

cross sectional area
fiber type
type of contraction

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ratio of actin to myosin

6:1

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what happens to cross sectional view of myofibril during muscle damage

increases

- more actin and myosin added by proteins

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mechanical properties that determine fiber type

contraction force
contraction time
time to 1/2 relaxtion
fatigue rate

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what is an isoform and how does it affect muscle fiber types

deviation from set protein

- changes mechanical properties

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how many total isoforms are there

86 myosin
6 action
516 total

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what is the size principle

fibers recruited slow to fast

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what is selective recruitment

-send out signals for high amp/high freq fibers and bypasss slow twitch

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what is rate coding

amplitude + frequency

-every muscles fibers of same MU has same rate coding

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what is the mechanical model of the musculotendinous unit?

contractile component: active
series eleastic component: passive (eligned end to end)
parallel elastic component: passive (elignd on top of eachother)

anatomical structures represented in mechanical model of MTU

CE: muscles fibers
SEC: tendons
PEC: epi-, peri-, and endomysiums

contribution of CE/SEC/PEC in concentric contractions of a constant load (ex405lbs)

CE= 100%

- PEC and SEC = 0%

contribution of CE/PEC/SEC in ecentric contraction of a contant load (ex405lbs)
-what does this tell you about the diff btwn 2 conctractions

CE= 80%
SEC= 15%
PEC= 5%
require less energy to eccentrically contract a constant load

contribution of CE/SEDC/PEC in concentric contractions of a constant intensity (1RM)

CE= 100%

- SEC and SEC= 0%

contribution of CE/SEDC/PEC in ecentric contractions of a constant intensity (ex 1RM)
-what does this tell you about the diff btwn the 2 contractions

CE= 100%
SEC= 15%
PEC= 5%
can manage more load during eccentric contraction during constant intensity

why does the force potential production decrease as muscle length shortens?
-why does it eventually reach 0?

# cross bridges formed decrease
b/c actin overlap on eachother and bottom one will block top one from binding to myosin
0 b/c: myosin acts as barrier to Z discs

why does the force potential production decrease as muscle length lengthens?
-why does it eventually reach 0?

# of cross bridges formed decreases
b/c actin doesnt have any overlap with myosin
0 b/c: no overlap at all

what happens to the tension and speed of contraction as the load increases in a concentric and eccentric contraction

con: -tension increases
- speed drecreases
ecc: -tension increasees
- speed increases

when can the max force be produced in a muscle in relation to veolcity

- isometric contraction | - velocity = 0

what happens to force produced by an eccentric contraction as velocity increases

-force increases

what happens to force produced by a concentric contraction as velocity increases

-force decreases

why does force decrease w/ concentric contractions as velocity increases

- greater load so need mroe cross bridges - more time needed to form more crossbridges - if you go too fast the actin and myosin do not have time to make cross bridges as they slide past eachother - increased latency period to transmit tension

equation of power | if decreased force what will power be?

P = F x V | -deceased power

factors affecting force production of the MTU | 6 of them

- CSA - fiber type - type of contraction - muscle fiber architecture - force length relationship - force velocity relationship

factors affecting velocity of contraction | 4 of them

- muscle length - shortening rate per sarcomere or muscles fiber (dependent on muscle fiber type) - fiber arrangement - the load needed to be moved

factors affecting muscles torque production

- all factors affecting force prodcution by MTU | - moment arm length

what happens to the force length curve as velocity increases

- curve gets smaller | - aka max point goes lower

what happends to force as velocity increases and length increases/decreases from rest length

-decrease

what happends to muscle length and moment arm length as jnt angle decreases

- muscle length decreases | - moment arm length increases, peaks, then decreases

factors affecting strength curve

- muscle length - moment arm length - velocity of contraction

what happens to strength curve as: - concentric contractions get faster - eccentric contractions get faster

- con:decreases - will have less torque at a set jnt angle - ecc: increases - will have more totque at set jnt angle