06/15/22 Dr. Sasho MacKenzie - HK 376 1 Muscle Mechanics Related to Chapter 11 in the text //highered.mcgraw-hill.com/sites/0072495855/student_view0/cha
Mar 23, 2016
04/25/23 Dr. Sasho MacKenzie - HK 376 1
Muscle Mechanics
Related to Chapter 11 in the text
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/
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peroneus longusperoneus brevis
flexor halucis longus
flexor digiturum longus
triceps surea
tibialis anterior
tibialis posterior
ext. hallucis longus
ext. digitorum longus
PreparationHintermann
Muscles crossing the ankle joint complex
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musclemuscle
fasciclefascicle
muscle fibre (cell)muscle fibre (cell)
myofibrilmyofibril
endomysiumendomysium
sacrolemmasacrolemma
perimysiumperimysium
epimysiumepimysium
fasciafascia
Muscle Schematic IllustrationMuscle Schematic Illustration
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I - Band
M Line
A - Band
MyofibrilMyofibril
Z Line
Huxley and Huxley, 1954
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filamentfilament Z-lineZ-line
sarcomeresarcomere
A-bandA-band I-bandI-band
MyofibrilMyofibril
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Current paradigm to describe muscle Current paradigm to describe muscle contractioncontraction
Hugh Huxley and Andrew Huxley published in Hugh Huxley and Andrew Huxley published in 1954 two independent papers (which were 1954 two independent papers (which were basically identical) to describe the sliding of the basically identical) to describe the sliding of the thick and thin filaments past one another.thick and thin filaments past one another.
sliding filament theorysliding filament theory
Refinished in 1957 by A. HuxleyRefinished in 1957 by A. Huxley cross bridge theory cross bridge theory
Cross bridge theoryCross bridge theory
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thick filamentthick filamentthin filamentthin filament
I-BandI-Band A-BandA-Band
Cross bridge theoryCross bridge theory
Z-lineZ-line Z-lineZ-line
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thickthickmyofilamentmyofilament
thinthinmyofilamentmyofilament
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I - Band
M Line
A - Band
thick filaments
Sliding filament model
thin filaments
1m
Z A I M
Huxley and Huxley, 1954
Z Line
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globular headglobular head
tail tail portionportion myosin myosin
moleculemolecule
thickthickmyofilamentmyofilament
Cross bridgesCross bridges
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6060oo
14.3 nm14.3 nm
43 nm43 nm
Cross bridgesCross bridges
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contractioncontraction
restrest cross-bridgecross-bridgethin filamentthin filament
thick filamentthick filament
slidingsliding
Cross bridge theoryCross bridge theory
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Muscle Force Depends on Four Factors
• Sarcomere (muscle) length• Velocity of muscle contraction• Activation level• Previous contraction history
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Fact:Fact:Muscles at very long and very Muscles at very long and very short lengths can not produce short lengths can not produce high forceshigh forces
Fact:Fact:Maximal force production of a Maximal force production of a muscle depends on its lengthmuscle depends on its length
Force-Length Relationship
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100100
7575
5050
2525
00
ascending limbascending limb
plateau regionplateau region
descending limbdescending limb
ForceForce[%][%]
Sarcomere lengthSarcomere length
Force-Length RelationshipForce-Length Relationship
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Force-Length RelationshipForce-Length Relationship
1.60 1.60 mm
0.10 0.10 mm 0.95 0.95 mm
Sarcomere = 1 z-line + 2 thin filament + 1 thick filament - overlapsSarcomere = 1 z-line + 2 thin filament + 1 thick filament - overlaps
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Force-Length Relationship
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aa
bb
cc1.51.5 2.02.0 2.52.5 3.03.03.53.5
aa bb
cc
100100
7575
5050
2525
00
sarcomere length sarcomere length [[m]m]
tens
ion
gene
rate
dte
nsio
n ge
nera
ted
Force-Length Relationship
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100100
7575
5050
2525
0000 1.271.27
3.603.60
11
2233 44
55
1.701.702.002.00
2.172.17
ascending limbascending limb
plateauplateau
descending limbdescending limb
ForceForce[%][%]
[%][%]
Force-Length Relationship
Sarcomere LengthSarcomere Length
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Ascending limb:Ascending limb:
Point 2: Point 2: Thin filaments overlap partially.Thin filaments overlap partially.A reduced number of cross-bridges A reduced number of cross-bridges can attach.can attach.
Point 1:Point 1: Complete overlap of thin filaments.Complete overlap of thin filaments.No cross-bridges can attach.No cross-bridges can attach.
General:General:descending limbdescending limb easy to understandeasy to understandascending limbascending limb more difficult to understandmore difficult to understand
Force-Length Relationship
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Starting position in sprintStarting position in sprint
Knee angle in weight liftingKnee angle in weight lifting
Design of weight lifting Design of weight lifting equipmentequipment
Design of bicyclesDesign of bicycles
Application of F-L Relationship
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Velocity of Muscle Contraction
mus
cle
forc
e
velocity of muscle contraction
eccentric concentric
isometric
– +
• Why less force for faster concentric contractions?• Why more force for eccentric contractions?
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STST FTFT
ForceForce
VelocityVelocity
PowerPower
STST
FTFT
VelocityVelocity
Force/Power - Velocity
ST = slow twitchST = slow twitch
FT = fast twitchFT = fast twitch
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Activation Level• It takes time for muscle to develop tension
1) Electrical signals must be sent from the brain (or spine) to activate muscles. The dynamics of muscle contraction once the signal reaches the muscle also takes time
• Even after activation is initiated, there is a delay in the force applied to the bones2) At the start of a contraction, the sarcomeres will
shorten but will not be able to generate their maximum force. The sarcomeres shorten because the tendons (and other elastic components of muscle) are stretched. The elastic components of muscles and tendons must be sufficiently stretched before the muscular force is transmitted to bone (Springs).
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Previous Contraction History• If a muscle is initially contracting isometrically and
is then stretched….….the muscle will produce a greater isometric force at it’s new length.
• Also, a concentric contraction immediately following an eccentric contraction will be more forceful.
• This is known as the “force enhancement” phenomenon and has been repeated in hundreds of experiments.
• There are several theories behind this behaviour but none are globally excepted.
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• In 1994, two men attempted to set a world bungee jumping record by performing the highest double bungee jump in history off of Royal George Bridge. The bridge was located in Colorado and was suspended 300 m above the Arkansas River. John (69.2 kg) and Rory (90.1 kg) used a bungee cord (linear spring) that was 50 m long. John was physically tied to the bungee while Rory simply held onto John. The duo had meticulously planned their jump so that they would come to a stop just as they touched the water. Rory would let go of John allowing him to make his way back to the top and reel John back to safety.
– Knowing that the 50 m long bungee cord had a stiffness (k) of 15, was their jump successful? In other words, did the pair come to rest just at the surface of the Arkansas River? (3)
– The top of the bungee was fixed to the middle of the underside of a huge metal I-beam. Assuming that 250 KJ of the strain energy was lost as heat (not converted back into kinetic energy) and that the pair dropped in a perfectly vertical path, what happened to John after Rory was dropped into the water? Make sure to include John’s velocity at 300 m above the surface of the river. (3)
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NEXT CLASSREAD CHAPTER 5
AND
Construct a flow chart depicting what the torque developed about a
joint depends on.
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musclemuscle
faciclefacicle
muscle fibre (cell)muscle fibre (cell)
myrofibrilmyrofibril
endomysiumendomysiumsacrolemmasacrolemma
perimysiumperimysium
epimysiumepimysium
fasciafascia
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Z LineZ Line M LineM Line
A BandA Band
thick filamentsthick filaments thin filamentsthin filaments
titintitin
I BandI Band
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globular headglobular head
tail portiontail portion myosin moleculemyosin molecule
thick myofilament thick myofilament
centre of filamentcentre of filament
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6060°°
14.3 nm14.3 nm
42.9 nm42.9 nm
cross bridges cross bridges on thick on thick myofilament myofilament
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actin chainsactin chainstropomyosintropomyosin
actin globuleactin globule troponintroponin
38.5 mm38.5 mm thin myofilamentthin myofilament
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1 µm1 µm
ZZ AA II MMTitinTitin
Sliding filament model:Sliding filament model:
Cross-section area of thick Cross-section area of thick filaments and thick-thin filaments and thick-thin myofilaments overlap myofilaments overlap
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1.01.0
0.50.5
0000 0.20.2 0.40.4 0.60.6 0.80.8
1.01.0
Force Force / / PowerPower[normalized][normalized]
ForceForcePowerPower
VelocityVelocity[normalized[normalized]]
Force/Power - Velocity
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Sarcomere Length
• Maximum overlap of myosin and actin allows for a maximum amount of cross-bridge connection and hence force.
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First experiments:First experiments:
•• Fenn and Marsh, 1935Fenn and Marsh, 1935
•• Hill, 1938Hill, 1938Found (“stumbled” onto) the Found (“stumbled” onto) the Force-velocity relationship while Force-velocity relationship while working on heat production of working on heat production of isolated frog skeletal muscle.isolated frog skeletal muscle.
Force-Velocity Relationship
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6060oo
6060oo
14.3 nm14.3 nm43 nm43 nm
14.3 nm14.3 nm
43 nm43 nm
model Imodel I
model IImodel II
model Imodel I
model IImodel II
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myosin filament
actin filament
AA
A1
B1
B2
M4
A4
MM11
Huxley 1969; Huxley and Simmons, 1971
Cross bridge theoryCross bridge theory
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Cross bridge theoryCross bridge theory
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Knee Extension
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0.00.0 0.50.5 1.01.0 1.51.5 2.02.0 2.5 2.5 [cm][cm]
00
2020
4040
6060
LengthLength
Force Force
passive structurespassive structures
Force-LengthForce-Length
AccumulatedAccumulatedForce-LengthForce-Length
Active and passive structures
[N][N]
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100100
7575
5050
2525
0000
3.603.60
11
2233 44
55
ascending limbascending limb
plateau regionplateau region
descending limbdescending limb
ForceForce[%][%]
Sarcomere lengthSarcomere length
1 z-line1 z-line 0.10 0.10 mm2 thin filament2 thin filament 1.90 1.90 mm1 thick filament1 thick filament 1.60 1.60 mmtotal length total length 3.60 3.60 mm
no cross bridges can attachno cross bridges can attach
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100100
7575
5050
2525
0000
3.603.60
11
2233 44
55
2.172.17
ascending limbascending limb descending limbdescending limb
ForceForce[%][%]
Sarcomere lengthSarcomere length
1 z-line1 z-line 0.10 0.10 mm2 length thin filament2 length thin filament 1.90 1.90 mm1 thick 1 thick filamentfilament no overlap no overlap 0.17 0.17 mmtotal length sarcomertotal length sarcomer 2.17 2.17 mm
all cross bridges can attachall cross bridges can attach
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100100
7575
5050
2525
0000
3.603.60
11
2233 44
55
2.002.002.172.17
ascending limbascending limb descending limbdescending limb
ForceForce[%][%]
Sarcomere lengthSarcomere length
1 z-line1 z-line 0.10 0.10 mm2 thin filament2 thin filament 1.90 1.90 mm1 thick filament no overlap1 thick filament no overlap 0.00 0.00 mmtotal length sarcomertotal length sarcomer 2.00 2.00 mm
all cross bridges can attachall cross bridges can attach