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Skeletal Muscle Contraction
Functions of skeletal muscles
To move the body limb by creating motion
To provide strength by
generating active force
To protect joints by absorbing shock
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Functions of connective tissues
within muscle
To provide gross structure to muscle
To generate passive tension against stretch
To transmit force to the bone and across the joint
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Definition
The act that muscle fibers generate tension which leads to the muscle
become shortening, remain the same length, or lengthening.
sliding Filament Mechanism¡G AF Huxley & HE Huxley, 1964
active shortening of sacromere, resulting from the relative movement of actin and myosin filaments
with retaining its original length
force of contraction is developed by the crossbridges of myosin
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Types based on changes in length
concentric contraction (shortening contraction)
definition¡G muscle contraction with the length of the entire muscle shortened
In daily activities, if the gravity is the only external force acting on the body,
the agonist muscle contracts concentrically during gravity-resisted motions
examples¡G
the abdominal muscles contract concentrically when the body sits up during curl-up (¥õª×°_§¤)
the triceps brachii muscle contracts concentrically when the body rises up during press up (¥ñ¦a®¼¨)
the quadriceps femoris contracts concentrically during upstairs
- Have you arm raise to the shoulder level and try to flex the elbow to 90
degrees. Which of the muscles in the arm responsible for this motion?
What type of the contraction? If you extend the elbow, what muscle
contracts and which type of contraction is?
- Similar to #1, if the elbow is flexed from 90 degrees to 130 degrees.
Which of the muscles in the arm responsible for this motion? What type of
the contraction? If you extend the elbow from 130 degrees to 90 degrees,
what muscle contracts and which type of contraction is?
- How to have your triceps brachii muscle contract eccentrically?
- If you lie down from sitting without using the abdominal muscles, what would happens?
isometric contraction (static contraction)
isos = equal¡F metron = measure
definition¡G muscle contraction with muscle length kept no change
The joint angle remains the same when an isometric strength is developed.
There is no motion existed during isometric contraction
eccentric contraction (lengthening contraction)
definition¡G muscle contraction with the length of the entire muscle lengthened
In daily activities, if the gravity is the only external force acting on the body,
the antagonist muscle contracts eccentrically during gravity-assisted motions
examples¡G
the abdominal muscles contract eccentrically when the body lies down during curl-up (¥õª×°_§¤)
the quadriceps contracts eccentrically during downstairs
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Types of muscle contraction, based on development of
tension
isotonic
iso = equal¡F tonus = tension
Muscle physiologists defined a kind of muscle contraction that
develops constant tension throughout the whole muscle excursion
as isotonic contraction; however, it is seldom seen in the living body
Clinicians use isotonic contraction commonly and refer to a muscle contraction
that causes a joint to move through some range of motion.
Even though the resistance remains the same,
the tension generated by the muscle is not equal tension because
- the moment arm to the joint axis is changing throughout the motion
- the resistance with respect to the gravity is changing throughout the motion
isometric
equal muscle length and same joint angle
zero motion speed with varying resistance
isokinetic
iso = equal¡F kinetos = move
definition¡G one kind of muscle contraction that occurs when the rate of movement is constant
not occur in the living body without using special machine (isokinetic dynamometer)
first introduced by Hislop and Perrine in 1967
equal motion speed with accommodating resistance
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comparison of different types of muscle contraction
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Tension |
Length |
Speed |
| isotonic |
varying |
varying |
varying |
| isometric |
varying |
equal |
zero |
| isokinetic |
accomodating resistance
(varying) |
varying |
constant |
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Length-Tension Relationship
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mechanical model of muscle fiber
contractile component¡G actin and myosin crossbridges structures
parallel elastic component¡G muscle connective tissue e.g. epimyosium, perimyosium, or endomyosium
series elastic component¡G connective tissues within the tendon
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tension generated by active contraction
resting length of a sacromere¡G the length that allows the greatest
number of cross-bridge attachments and the greatest potential active force
active length-tension curve¡G an inverted U-shape with its peak at the resting length
tension generated by passive stretch
developed when series and parallel elastic components are stretched
passive length-tension curve¡G the tissue is slack before stretched and then
the tension builds as an exponential function
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total length tension curve of muscle
at shortened lengths¡G active contraction dominates force generation
just beyond its resting length¡G passive tension begins to contribute and active tension is compromised
at more elongated lengths¡G passive tension accounts for most of the total force
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Force-Velocity Relationship
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