Proper@es of Muscle Plan for Today Whats cool about muscle? Muscle - - PDF document

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Proper@es of Muscle Plan for Today Whats cool about muscle? Muscle - - PDF document

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2/2/16 Musculoskeletal Biomechanics BIOEN 520 | ME 599R Session 10 Structure-Func@on- Proper@es of Muscle Plan for Today Whats cool about muscle? Muscle structure and biology Basic muscle proper@es Force-length rela@onship

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Musculoskeletal Biomechanics

BIOEN 520 | ME 599R

Session 10

Structure-Func@on- Proper@es of Muscle

Plan for Today

  • What’s cool about muscle?
  • Muscle structure and biology
  • Basic muscle proper@es

§ Force-length rela@onship § Force-velocity rela@onship

  • Tools for evalua@ng muscle func@on
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MUSCLE: The Ul@mate Actuator

Control

Muscles turn

  • n and off

Energetics

Muscles get and use energy

Mechanics

Muscles generate force and motion

MUSCLE: The Ul@mate Actuator

  • Muscle links your CNS to the world.
  • The structure is fantas@c!

§ cross bridges working together § fascicle structure and metabolic machinery § architecture of whole muscles

  • Math represents the biology preUy well.
  • Tastes great medium rare.
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Basic Rules of Muscle Func@on

  • Muscles pull, they don’t push.
  • Muscles are grouped into

antagonist pairs.

  • Movement involves coordina@on
  • f many muscles.
  • Mul@ple muscles act at each

joint.

  • Muscles with different shapes,

sizes, and aUachments generate different forces and mo@ons.

Sartorius Gastrocnemius

Hierarchical Muscle Structure

muscle fascicle fiber = cell myofibril sarcomere, 2-3µm

adapted from Scientific American, September 2000

sarcoplasmic reticulum filaments actin myosin

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Fascicles are groups of fibers

  • One can dissect out muscle

fascicles.

  • Under a light microscope a

stripped paUern is seen.

  • A muscle cell may be

10-100µm in diameter and 1-30 cm long.

McNeill Alexander, How Animals Move

Fascicles are groups of fibers

  • Under an electron

microscope, one can clearly see individual myofibrils

  • The source of the stripped

paUern (Z-disks) are also seen

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Structure of a Sarcomere

Schematic of Sarcomere Myofibril Electron Microscope View Schematic of Sarcomere

Force is Developed at the Ac@n-Myosin Cross Bridge.

Thick filament is made of myosin (head and tail) Ac@n is the primary component of thin filaments (10nm diameter)

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Muscle Shortens as the Proteins Slide Past Each Other.

When muscle is ac@vated the myosin heads aUach to the thin filaments and form cross bridges

McNeill Alexander, How Animals Move

Muscle Shortens as the Proteins Slide Past Each Other.

SDSU

[http://www.sci.sdsu.edu/movies/actin_myosin_gif.html]

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Plan for Today

  • What’s cool about muscle?
  • Muscle structure and biology
  • Basic muscle proper@es

§ Force-length rela@onship § Force-velocity rela@onship

  • Tools for evalua@ng muscle func@on

Sarcomere length, µm Values for frog muscle; different values for human muscle

Force-Length Relationship

Length Velocity Orientation Size

Z-disk Z-disk actin myosin actin

SARCOMERE

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2/2/16 8 Force-Length Relationship

Length Velocity Orientation Size

Z-disk Z-disk actin myosin actin

Sarcomere length, µm Values for frog muscle; slightly different values for human skeletal muscle

Force-Length Relationship

WHOLE MUSCLE Length Velocity Orientation Size These curves apply to ISOMETRIC muscle

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Length Force 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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2/2/16 10 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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2/2/16 11 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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2/2/16 12 Fiber Orientation Pennate Muscle Parallel Fibered

Length Velocity Orientation Size Fewer, Longer Fibers More, Shorter Fibers Pennation Angle

Physiological Cross-Sectional Area Pennate Muscle Parallel 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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2/2/16 13 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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Plan for Today

  • What’s cool about muscle?
  • Muscle structure and biology
  • Basic muscle proper@es

§ Force-length rela@onship § Force-velocity rela@onship

  • Tools for evalua@ng muscle func@on

Tools for evalua@ng muscle func@on

  • In vivo muscle func@on
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Tools for evalua@ng muscle func@on

  • In vivo muscle func@on

Tools for evalua@ng muscle func@on

  • In vivo muscle func@on
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Tools for evalua@ng muscle func@on

  • In silico muscle func@on

Probe parameters that are difficult to measure Visualize complex movement patterns Perform “what if” studies Identify cause-effect relationships

Musculoskeletal Models

MR images 3D reconstruction line muscles combined with geometric assumptions

Arnold et al., 2000

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Musculoskeletal Model

21 Cadavers 82.5 ± 9.42 years

Arnold, et al., Clin Orthop Relat Res 467, 1074-1082, 2009. Ward, S.R., et al., Clin Orthop Relat Res 467, 1074-1082, 2009.

Models Muscle Contrac@on Dynamics

FT = fT ⋅ F

Max M

F M = a⋅ fAL ⋅ fV + fPL

( )⋅ F M

Max

  • 1. Thelen, D.G., Anderson, F.C., Delp, S.L., J Biomech 36, 321-328, 2003
  • 2. Zajac, F. E. Crit. Rev. Biomed. Eng. 17, 359–411, 1989.

1 2 1,2

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Musculoskeletal Simula@ons OpenSim

h"p://opensim.stanford.edu

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Musculoskeletal Model

  • 23 body

segments

  • 92 muscle-

tendon actuators

OpenSim Repository

Running: Hamner et al, 2010 Lumbar-spine: Christophy et al, 2011 Lower-extremity: Arnold et al, 2010 Shoulder: Ma@as et al, in prep.

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Download and try the tutorials!

h"p://opensim.stanford.edu

ME412/512: Biomechanics of Movement

Cour

  • urse

e Object Objectiv ives es

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.

Tues uesday day/Thur hursday day Wint inter er 2017 2017

Prerequisites: Statics, Dynamics, Differential Equations

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A Quick Intro to Muscle

  • What’s cool about muscle?
  • Muscle structure and biology
  • Basic muscle proper@es

§ Force-length rela@onship § Force-velocity rela@onship

  • Tools for evalua@ng muscle func@on

THE END