Download Muscle Mechanics Lecture

Muscle Mechanics
Related to Chapter 11 in the text
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter10/
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Preparation
Hintermann
flexor digiturum longus
flexor halucis longus
tibialis posterior
peroneus brevis
peroneus longus
tibialis anterior
ext. hallucis longus
ext. digitorum longus
triceps surea
Muscles crossing the ankle joint complex
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Muscle Schematic Illustration
muscle
fascia
fascicle
epimysium
muscle fibre (cell)
perimysium
myofibril
sacrolemma
endomysium
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Myofibril
I - Band
A - Band
Z Line
M Line
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Huxley and
Huxley, 1954
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Myofibril
sarcomere
IA-band band
filament
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Z-line
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Cross bridge theory
Current paradigm to describe muscle
contraction
Hugh Huxley and Andrew Huxley published in
1954 two independent papers (which were
basically identical) to describe the sliding of the
thick and thin filaments past one another.
 sliding filament theory
Refinished in 1957 by A. Huxley
 cross bridge theory
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Cross bridge theory
thick filament
thin filament
Z-line
I-Band
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Z-line
A-Band
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thick
myofilament
thin
myofilament
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Huxley and Huxley, 1954
I - Band A - Band
Z Line
M Line
Sliding filament model
Z
A
I
M
1mm
thick filaments thin filaments
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Cross bridges
globular head
tail
portion
myosin
molecule
thick
myofilament
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Cross bridges
60o
14.3 nm
43 nm
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Cross bridge theory
rest
cross-bridge
thin filament
thick filament
contraction
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sliding
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Muscle Force Depends on
Four Factors
•
•
•
•
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Sarcomere (muscle) length
Velocity of muscle contraction
Activation level
Previous contraction history
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Force-Length Relationship
Fact:
Muscles at very long and very
short lengths can not produce
high forces
Fact:
Maximal force production of a
muscle depends on its length
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Force-Length Relationship
Force
[%]
plateau region
100
75
50
ascending limb
descending limb
25
0
Sarcomere length
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Force-Length Relationship
Sarcomere = 1 z-line + 2 thin filament + 1 thick filament - overlaps
0.10 mm
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0.95 mm
1.60 mm
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Force-Length Relationship
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Force-Length Relationship
a b
a
b
tension generated
100
75
50
25
c
0
1.5
c
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2.0
2.5
3.0
3.5
sarcomere length
[mm]
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Force-Length Relationship
Force
[%]
plateau
100
2
3
4
75
50
ascending limb
25
0
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1
0 1.27
descending limb
2.17
2.00
1.70
3.60
[%]
Sarcomere Length
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Force-Length Relationship
General:
descending limb
ascending limb
easy to understand
more difficult to understand
Ascending limb:
Point 2:
Thin filaments overlap partially.
A reduced number of cross-bridges
can attach.
Point 1:
Complete overlap of thin filaments.
No cross-bridges can attach.
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Application of F-L Relationship
 Starting position in sprint
 Knee angle in weight lifting
 Design of weight lifting
equipment
 Design of bicycles
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Velocity of Muscle Contraction
eccentric
–
muscle force
isometric
concentric
+
velocity of muscle contraction
• Why less force for faster concentric contractions?
• Why more force for eccentric contractions?
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Force/Power - Velocity
Force
Power
ST = slow twitch
FT = fast twitch
FT
ST
ST
FT
Velocity
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Velocity
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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 bones
2) 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.
–
–
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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 CLASS
READ CHAPTER 5
AND
Construct a flow chart depicting
what the torque developed about a
joint depends on.
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muscle
fascia
facicle
muscle fibre (cell)
epimysium
perimysium
myrofibril
sacrolemma
endomysium
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I Band
Z Line
thick filaments
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A Band
M Line
titin
thin filaments
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globular head
tail portion
myosin molecule
thick myofilament
centre of filament
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60°
cross bridges
on thick
myofilament
14.3 nm
42.9 nm
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actin globule
troponin
thin myofilament
38.5 mm
tropomyosin
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actin chains
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Sliding filament model:
Titin
Z
A
I
M
1 µm
Cross-section area of thick
filaments and thick-thin
myofilaments overlap
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Force/Power - Velocity
Force /
Power
Force
Power
[normalized]
1.0
0.5
Velocity
0
0
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0.2
0.4
0.6
0.8 1.0[normalized
]
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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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Force-Velocity Relationship
First experiments:
• Fenn and Marsh, 1935
• Hill, 1938
Found (“stumbled” onto) the
Force-velocity relationship while
working on heat production of
isolated frog skeletal muscle.
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60o
model I
14.3 nm
43 nm
60o
model II
14.3 nm
43 nm
model I
model II
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Cross bridge theory
myosin filament
A
B
B
2
1
actin filament
M
M
4
1
A
Huxley 1969; Huxley and Simmons, 1971
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1
q
A
4
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Cross bridge theory
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Knee Extension
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Active and passive structures
Force
[N]
60
Accumulated
Force-Length
passive structures
40
Force-Length
20
Length
0
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0.0 0.5
[cm]
1.0
1.5
2.0
2.5
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no cross bridges can attach
Force
[%]
plateau region
3
100
1 z-line
2 thin filament
1 thick filament
total length
0.10 mm
1.90 mm
1.60 mm
3.60 mm
4
2
75
50
ascending
limb
descending limb
25
1
0
0
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5
Sarcomere length
3.60
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all cross bridges can attach
Force
[%]
3
100
4
1 z-line
2 length thin filament
1 thick filament no overlap
total length sarcomer
0.10 mm
1.90 mm
0.17 mm
2.17 mm
2
75
50
ascending
limb
descending limb
25
1
0
0
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5
2.17
Sarcomere length
3.60
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all cross bridges can attach
1 z-line
2 thin filament
1 thick filament no overlap
total length sarcomer
Force
[%]
3
100
0.10 mm
1.90 mm
0.00 mm
2.00 mm
4
2
75
50
ascending
limb
descending limb
25
1
0
0
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5
2.17
3.60
2.00
Sarcomere length
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