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MusculoskeletalBiomechanicsBIOEN520|ME599R
Session10Structure-Func@on-Proper@esofMuscle
PlanforToday
• What’scoolaboutmuscle?
• Musclestructureandbiology
• Basicmuscleproper@es§ Force-lengthrela@onship§ Force-velocityrela@onship
• Toolsforevalua@ngmusclefunc@on
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MUSCLE:TheUl@mateActuator
Control Muscles turn
on and off
Energetics Muscles get and
use energy
Mechanics Muscles generate force and motion
MUSCLE:TheUl@mateActuator• MusclelinksyourCNStotheworld.
• Thestructureisfantas@c!§ crossbridgesworkingtogether§ fasciclestructureandmetabolicmachinery§ architectureofwholemuscles
• MathrepresentsthebiologypreUywell.
• Tastesgreatmediumrare.
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BasicRulesofMuscleFunc@on
• Musclespull,theydon’tpush.
• Musclesaregroupedintoantagonistpairs.
• Movementinvolvescoordina@onofmanymuscles.
• Mul@plemusclesactateachjoint.
• Muscleswithdifferentshapes,sizes,andaUachmentsgeneratedifferentforcesandmo@ons.
Sartorius Gastrocnemius
HierarchicalMuscleStructure
muscle
fascicle
fiber = cell
myofibril
sarcomere, 2-3µm
adapted from Scientific American, September 2000
sarcoplasmic reticulum
filamen
ts
actin myosin
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Fasciclesaregroupsoffibers
• Onecandissectoutmusclefascicles.
• UnderalightmicroscopeastrippedpaUernisseen.
• Amusclecellmaybe10-100µmindiameterand1-30cmlong.
McNeill Alexander, How Animals Move
Fasciclesaregroupsoffibers
• Underanelectronmicroscope,onecanclearlyseeindividualmyofibrils
• ThesourceofthestrippedpaUern(Z-disks)arealsoseen
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StructureofaSarcomere
Schematic of Sarcomere
Myofibril Electron Microscope View
Schematic of Sarcomere
ForceisDevelopedattheAc@n-MyosinCrossBridge.
Thickfilamentismadeofmyosin(headandtail)
Ac@nistheprimarycomponentofthinfilaments(10nmdiameter)
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MuscleShortensastheProteinsSlidePastEachOther.
Whenmuscleisac@vatedthemyosinheadsaUachtothethinfilamentsandformcrossbridges
McNeill Alexander, How Animals Move
MuscleShortensastheProteinsSlidePastEachOther.
SDSU
[http://www.sci.sdsu.edu/movies/actin_myosin_gif.html]
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PlanforToday
• What’scoolaboutmuscle?
• Musclestructureandbiology
• Basicmuscleproper@es§ Force-lengthrela@onship§ Force-velocityrela@onship
• Toolsforevalua@ngmusclefunc@on
Sarcomere length, µm Values for frog muscle; different values for human muscle
Force-Length Relationship
Length Velocity Orientation Size
Z-disk Z-diskactinmyosinactinSARCOMERE
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Force-Length Relationship
Length Velocity Orientation Size
Z-disk Z-diskactinmyosinactinSarcomere length, µm
Values for frog muscle; slightly different values for human skeletal muscle
This slide is just for printing the PDFs to go on-line.
Force-Length Relationship
WHOLE MUSCLE
Length Velocity Orientation Size
These curves apply to ISOMETRIC muscle
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Length
Forc
e
Passive
Passive Properties
Force-Velocity Relationship
Length Velocity Orientation Size
Rate of cross-bridge formation
Breaking cross-bridges?
Concentric Contraction
Eccentric Contraction
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Force-Velocity Relationship
Length Velocity Orientation Size Power = Force x Velocity Power = Force x Velocity
Why does a bike have gears?
Force-Length-Velocity Relationship
Length Velocity Orientation Size
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Fiber Orientation
Length Velocity Orientation Size
http://www.rad.washington.edu/academics/academic-sections/msk/muscle-atlas
• What happens to muscle force and excursion if there are more sarcomeres in parallel? In series?
F
F
2d
d
F 2F
d d
Effect of number and length of fibers
Length Velocity Orientation Size
More fibers = More force Longer fiber = Longer excursion
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Fiber Orientation
Pennate MuscleParallel Fibered
Length Velocity Orientation Size
Fewer, Longer Fibers
More, Shorter Fibers
Pennation Angle
Physiological Cross-Sectional Area
Pennate MuscleParallel Fibered
Length Velocity Orientation Size
Physiological cross-sectional area (PCSA) is proportional to force.
Less Force More Excursion
More Force Less Excursion
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Compare muscles
Sartorius Gastrocnemius
Which muscle can generate more force? More excursion?
Muscle Moment Arms
Length Velocity Orientation Size Moment Arm
Muscles pull on bones to create a moment about a joint.
Moment Arm § Perpendicular distance between
muscle’s line of action and joint center § Muscle length change required for
joint angle change § Changes with joint angle
Moment = Force x Moment Arm
Which muscle would generate greater moment?
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PlanforToday
• What’scoolaboutmuscle?
• Musclestructureandbiology
• Basicmuscleproper@es§ Force-lengthrela@onship§ Force-velocityrela@onship
• Toolsforevalua@ngmusclefunc@on
Toolsforevalua@ngmusclefunc@on
• Invivomusclefunc@on
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Toolsforevalua@ngmusclefunc@on
• Invivomusclefunc@on
Toolsforevalua@ngmusclefunc@on
• Invivomusclefunc@on
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Toolsforevalua@ngmusclefunc@on• Insilicomusclefunc@on
Probe parameters
that are difficult to measure
Visualize complex
movement patterns
Perform “what if” studies
Identify cause-effect relationships
MusculoskeletalModels
MR images 3D reconstruction line muscles combined with geometric assumptions Arnold et al., 2000
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MusculoskeletalModel
21Cadavers82.5±9.42years
Arnold, et al., Clin Orthop Relat Res 467, 1074-1082, 2009. Ward, S.R., et al., Clin Orthop Relat Res 467, 1074-1082, 2009.
ModelsMuscleContrac@onDynamics
FT = fT ⋅FMaxM
FM = a ⋅ fAL ⋅ fV + fPL( ) ⋅FMMax
1. Thelen,D.G.,Anderson,F.C.,Delp,S.L.,JBiomech36,321-328,20032. Zajac,F.E.Crit.Rev.Biomed.Eng.17,359–411,1989.
1 21,2
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MusculoskeletalSimula@ons
OpenSimh"p://opensim.stanford.edu
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MusculoskeletalModel
• 23 body segments
• 92 muscle-
tendon actuators
OpenSimRepository
Running:Hamneretal,2010
Lumbar-spine:Christophyetal,2011
Lower-extremity:Arnoldetal,2010
Shoulder:Ma@asetal,inprep.
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Downloadandtrythetutorials!h"p://opensim.stanford.edu
ME412/512:BiomechanicsofMovementCourse Objectives After completing this course, you will be able to: 1) Describe the biological, mechanical, and neurological mechanisms by which muscles produce movement 2) Identify and use engineering tools that are used to study movement 3) Write and solve equations of motion for simple models of human movement 4) Apply biomechanics principles to “real-world” clinical and biomechanical research.
Tuesday/Thursday Winter 2017 Prerequisites: Statics, Dynamics, Differential Equations
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AQuickIntrotoMuscle
• What’scoolaboutmuscle?
• Musclestructureandbiology
• Basicmuscleproper@es§ Force-lengthrela@onship§ Force-velocityrela@onship
• Toolsforevalua@ngmusclefunc@on
THEEND