Neuromuscular Fundamentals

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Neuromuscular Fundamentals

• Anatomy and Kinesiology
• 420024

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Outline

• Introduction
• Structure and Function
• Fiber Arrangement
• Muscle Actions
• Role of Muscles
• Neural Control
• Factors that Affect Muscle Tension

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Introduction

• Responsible for movement of body and all of its
  joints
• Muscles also provide
• Over 600 skeletal muscles comprise approximately
  40 to 50 of body weight
• 215 pairs of skeletal muscles usually work in
  cooperation with each other to perform opposite
  actions at the joints which they cross
• Aggregate muscle action

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Muscle Tissue Properties

• Irritability or Excitability
• Contractility
• Extensibility
• Elasticity

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Outline

• Introduction
• Structure and Function
• Fiber Arrangement
• Muscle Actions
• Role of Muscles
• Neural Control
• Factors that Affect Muscle Tension

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Structure and Function

• Nervous system structure
• Muscular system structure
• Neuromuscular function

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Figure 14.1, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Nervous System Structure

• Integration of information from millions of
  sensory neurons ? action via motor neurons

Figure 12.1, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Nervous System Structure

• Organization
• Brain
• Spinal cord
• Nerves
• Fascicles
• Neurons

Figure 12.2, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
Figure 12.7, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Nervous System Structure

• Both sensory and motor neurons in nerves

Figure 12.11, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Nervous System Structure

• The neuron Functional unit of nervous tissue
  (brain, spinal cord, nerves)
• Dendrites
• Cell body
• Axon
• Myelin sheath
• Nodes of Ranvier
• Terminal branches
• Axon terminals
• Synaptic vescicles
• Neurotransmitter

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Dendrites
Cell body
Axon
Myelin sheath
Node of Ranvier
Terminal ending
Terminal branch
Figure 12.4, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Figure 12.8, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
Terminal ending
Synaptic vescicle
Neurotransmitter Acetylcholine (ACh)
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Figure 12.19, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Structure and Function

• Nervous system structure
• Muscular system structure
• Neuromuscular function

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Classification of Muscle Tissue

• Three types
• 1. Smooth muscle
• 2. Cardiac muscle
• 3. Skeletal muscle

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Muscular System Structure

• Organization
• Muscle (epimyseum)
• Fascicle (perimyseum)
• Muscle fiber (endomyseum)
• Myofibril
• Myofilament
• Actin and myosin
• Other Significant Structures
• Sarcolemma
• Transverse tubule
• Sarcoplasmic reticulum
• Tropomyosin
• Troponin

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Figure 10.1, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Figure 10.4, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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http//staff.fcps.net/cverdecc/Adv20AP/Notes/Mus
cle20Unit/sliding20filament20theory/slidin16.jp
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Figure 10.8, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Structure and Function

• Nervous system structure
• Muscular system structure
• Neuromuscular function

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Neuromuscular Function

• Basic Progression
• 1. Nerve impulse
• 2. Neurotransmitter release
• 3. Action potential along sarcolemma
• 4. Calcium release
• 5. Coupling of actin and myosin
• 6. Sliding filaments

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Nerve Impulse

• What is a nerve impulse?
• -Transmitted electrical charge
• -Excites or inhibits an action
• -An impulse that travels along an axon is an
  ACTION POTENTIAL

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Nerve Impulse

• How does a neuron send an impulse?
• -Adequate stimulus from dendrite
• -Depolarization of the resting membrane
  potential
• -Repolarization of the resting membrane
  potential
• -Propagation

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Nerve Impulse

• What is the resting membrane potential?
• -Difference in charge between inside/outside of
  the neuron

-70 mV
Figure 12.9, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Nerve Impulse

• What is depolarization?
• -Reversal of the RMP from 70 mV to 30mV

Propagation of the action potential
Figure 12.9, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Nerve Impulse

• What is repolarization?
• -Return of the RMP to 70 mV

Figure 12.9, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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30 mV
-70 mV
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Neuromuscular Function

• Basic Progression
• 1. Nerve impulse
• 2. Neurotransmitter release
• 3. Action potential along sarcolemma
• 4. Calcium release
• 5. Coupling of actin and myosin
• 6. Sliding filaments

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Release of the Neurotransmitter

• Action potential ? axon terminals
• 1. Calcium uptake
• 2. Release of synaptic vescicles (ACh)
• 3. Vescicles release ACh
• 4. ACh binds sarcolemma

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Figure 12.8, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
Ca2
ACh
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Figure 14.5, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Neuromuscular Function

• 1. Nerve impulse
• 2. Neurotransmitter release
• 3. Action potential along sarcolemma
• 4. Calcium release
• 5. Coupling of actin and myosin
• 6. Sliding filaments

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Ach
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AP Along the Sarcolemma

• Action potential ? Transverse tubules
• 1. T-tubules carry AP inside
• 2. AP activates sarcoplasmic reticulum

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Figure 14.5, Marieb Mallett (2003). Human
Anatomy. Benjamin Cummings.
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Neuromuscular Function

• 1. Nerve impulse
• 2. Neurotransmitter release
• 3. Action potential along sarcolemma
• 4. Calcium release
• 5. Coupling of actin and myosin
• 6. Sliding Filaments

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Calcium Release

• AP ? T-tubules ? Sarcoplasmic reticulum
• 1. Activation of SR
• 2. Calcium released into sarcoplasm

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CALCIUM RELEASE
Sarcolemma
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Neuromuscular Function

• 1. Nerve impulse
• 2. Neurotransmitter release
• 3. Action potential along sarcolemma
• 4. Calcium release
• 5. Coupling of actin and myosin
• 6. Sliding filaments

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Coupling of Actin and Myosin

• Tropomyosin
• Troponin

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Blocked
Coupling of actin and myosin
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Neuromuscular Function

• 1. Nerve impulse
• 2. Neurotransmitter release
• 3. Action potential along sarcolemma
• 4. Calcium release
• 5. Coupling of actin and myosin
• 6. Sliding filaments

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Sliding Filament Theory

• Basic Progression of Events
• 1. Cross-bridge
• 2. Power stroke
• 3. Dissociation
• 4. Reactivation of myosin

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Cross-Bridge

• Activation of myosin via ATP
• -ATP ? ADP Pi Energy
• -Activation ? cocked position

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Power Stroke

• ADP Pi are released
• Configurational change
• Actin and myosin slide

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Dissociation

• New ATP binds to myosin
• Dissociation occurs

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Reactivation of Myosin Head

• ATP ? ADP Pi Energy
• Reactivates the myosin head
• Process starts over
• Process continues until
• -Nerve impulse stops
• -AP stops
• -Calcium pumped back into SR
• -Tropomyosin/troponin back to original position

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Outline

• Introduction
• Structure and Function
• Fiber Arrangement
• Muscle Actions
• Role of Muscles
• Neural Control
• Factors that Affect Muscle Tension

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Shape of Muscles Fiber Arrangement

• Muscles have different shapes fiber
  arrangements
• Shape fiber arrangement affects

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Shape of Muscles Fiber Arrangement

• Two major types of fiber arrangements

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Fiber Arrangement - Parallel

• Parallel muscles
• Categorized into following shapes
• Flat
• Fusiform
• Strap
• Radiate
• Sphincter or circular

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Fiber Arrangement - Parallel

• Flat muscles

Modified from Van De Graaff KM Human anatomy, ed
6, Dubuque, IA, 2002, McGraw-Hill.
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Fiber Arrangement - Parallel

• Fusiform muscles

Figure 3.3. Hamilton, Weimar Luttgens (2005).
Kinesiology Scientific basis for human motion.
McGraw-Hill.
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Fiber Arrangement - Parallel

• Strap muscles

Figure 8.7. Hamilton, Weimar Luttgens (2005).
Kinesiology Scientific basis for human motion.
McGraw-Hill.
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Fiber Arrangement - Parallel

• Radiate muscles

Modified from Van De Graaff KM Human anatomy, ed
6, Dubuque, IA, 2002, McGraw-Hill.
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Fiber Arrangement - Parallel

• Sphincter or circular muscles

Modified from Van De Graaff KM Human anatomy, ed
6, Dubuque, IA, 2002, McGraw-Hill.
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Fiber Arrangement - Pennate

• Pennate muscles

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Fiber Arrangement - Pennate

• Categorized based upon the exact arrangement
  between fibers tendon

Modified from Van De Graaff KM Human anatomy, ed
6, Dubuque, IA, 2002, McGraw-Hill.
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Fiber Arrangement - Pennate

• Unipennate muscles

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Fiber Arrangement - Pennate

• Bipennate muscle

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Fiber Arrangement - Pennate

• Multipennate muscles
• Bipennate unipennate produce more force than
  multipennate

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Outline

• Introduction
• Structure and Function
• Fiber Arrangement
• Muscle Actions
• Role of Muscles
• Neural Control
• Factors that Affect Muscle Tension

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Muscle Actions Terminology

• Origin (Proximal Attachment)

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Muscle Actions Terminology

• Insertion (Distal Attachment)

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Muscle Actions Terminology

• When a particular muscle is activated
• Examples
• Bicep curl vs. chin-up
• Hip extension vs. RDL

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Muscle Actions

• Action
• Contraction

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Muscle Actions

• Muscle actions can be used to cause, control, or
  prevent joint movement or

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Types of Muscle Actions
MUSCLE ACTION (under tension)
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Types of Muscle Actions

• Isometric action

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Types of Muscle Actions

• Isotonic (same tension)
• Isotonic contractions are either concentric
  (shortening) or eccentric (lengthening)

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Types of Muscle Actions

• Concentric contractions involve muscle developing
  tension as it shortens
• Eccentric contractions involve the muscle
  lengthening under tension

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What is the role of the elbow extensors in each
phase?
Modified from Shier D, Butler J, Lewis R Holes
human anatomy physiology, ed 9, Dubuque, IA,
2002, McGraw-Hill
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Types of Muscle Actions

• Isokinetics

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Types of Muscle Actions

• Movement may occur at any given joint without any
  muscle contraction whatsoever

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Outline

• Introduction
• Structure and Function
• Fiber Arrangement
• Muscle Actions
• Role of Muscles
• Neural Control
• Factors that Affect Muscle Tension

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Role of Muscles

• Agonist muscles

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Role of Muscles

• Antagonist muscles

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Role of Muscles

• Stabilizers

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Role of Muscles

• Synergist

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Role of Muscles

• Neutralizers

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Outline

• Introduction
• Structure and Function
• Fiber Arrangement
• Muscle Actions
• Role of Muscles
• Neural Control
• Factors that Affect Muscle Tension

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Factors That Affect Muscle Tension

• Number Coding and Rate Coding
• Length-Tension Relationship
• Force-Velocity Relationship
• Angle of Pull
• Uniarticular vs. Biarticular Muscles
• Cross-sectional Diameter
• Muscle Fiber Type
• Pennation

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Number Coding Rate Coding

• Difference between lifting a minimal vs. maximal
  resistance is the number of muscle fibers
  recruited (crossbridges)
• The number of muscle fibers recruited may be
  increased by

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Number Coding Rate Coding

• Number of muscle fibers per motor unit varies
  significantly

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Number Coding Rate Coding

• As stimulus strength increases from threshold,
  more motor units (Number Coding) are recruited
  overall muscle contraction force increases in a
  graded fashion

From Seeley RR, Stephens TD, Tate P Anatomy
physiology, ed 7, New York, 2006, McGraw-Hill.
90
Number Coding Rate Coding

• Greater contraction forces may also be achieved
  by increasing the frequency or motor unit
  activation (Rate Coding)
• Phases of a single muscle fiber contraction or
  twitch
• Stimulus
• Latent period
• Contraction phase
• Relaxation phase

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Number Coding Rate Coding

• Latent period
• Contraction phase
• Relaxation phase

From Powers SK, Howley ET Exercise physiology
theory and application to fitness and
performance, ed 4, New York, 2001 , McGraw-Hill.
92
Number Coding Rate Coding

• Summation
• When successive stimuli are provided before
  relaxation phase of first twitch has completed,
  subsequent twitches combine with the first to
  produce a sustained contraction
• Generates a greater amount of tension than single
  contraction would produce individually
• As frequency of stimuli increase, the resultant
  summation increases accordingly producing
  increasingly greater total muscle tension

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Number Coding Rate Coding

• Tetanus

From Powers SK, Howley ET Exercise physiology
theory and application to fitness and
performance, ed 4, New York, 2001 , McGraw-Hill.
94
All or None Principle

• Motor unit
• Typical muscle contraction
• All or None Principle

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Factors That Affect Muscle Tension

• Number Coding and Rate Coding
• Length-Tension Relationship
• Force-Velocity Relationship
• Angle of Pull
• Uniarticular vs. Biarticular Muscles
• Cross-sectional Diameter
• Muscle Fiber Type
• Pennation

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Length - Tension Relationship

• Maximal ability of a muscle to develop tension
  exert force varies depending upon the length of
  the muscle during contraction

Passive Tension
Active Tension
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Length - Tension Relationship

• Generally, depending upon muscle involved

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Length - Tension Relationship

• Generally, depending upon muscle involved

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Figure 20.2, Plowman and Smith (2002). Exercise
Physiology, Benjamin Cummings.
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Factors That Affect Muscle Tension

• Number Coding and Rate Coding
• Length-Tension Relationship
• Force-Velocity Relationship
• Angle of Pull
• Uniarticular vs. Biarticular Muscles
• Cross-sectional Diameter
• Muscle Fiber Type
• Pennation

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Force Velocity Relationship

• When muscle is contracting (concentrically or
  eccentrically) the rate of length change is
  significantly related to the amount of force
  potential

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Force Velocity Relationship

• Maximum concentric velocity minimum resistance
• As load increases, concentric velocity decreases
• Eventually velocity 0 (isometric action)

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Force Velocity Relationship

• As load increases beyond muscles ability to
  maintain an isometric contraction
• As load increases
• Eventually

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Muscle Force Velocity Relationship

• Indirect relationship between force (load) and
  concentric velocity
• Direct relationship between force (load) and
  eccentric velocity

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Factors That Affect Muscle Tension

• Number Coding and Rate Coding
• Length-Tension Relationship
• Force-Velocity Relationship
• Angle of Pull
• Uniarticular vs. Biarticular Muscles
• Cross-sectional Diameter
• Muscle Fiber Type
• Pennation

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Angle of Pull

• Angle between the line of pull of the muscle
  the bone on which it inserts (angle toward the
  joint)
• With every degree of joint motion, the angle of
  pull changes
• Joint movements insertion angles involve mostly
  small angles of pull

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Angle of Pull

• Angle of pull changes as joint moves through ROM
• Most muscles work at angles of pull less than 50
  degrees
• Amount of muscular force needed to cause joint
  movement is affected by angle of pull Why?

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Angle of Pull

• Rotary component - Acts perpendicular to long
  axis of bone (lever)

Modified from Hall SJ Basic biomechanics, New
York, 2003, McGraw-Hill.
109
Angle of Pull

• If angle lt 90 degrees, the parallel component is
  a stabilizing force
• If angle gt 90 degrees, the force is a dislocating
  force

What is the effect of gt/lt 90 deg on ability to
rotate the joint forcefully?
Modified from Hall SJ Basic biomechanics, New
York, 2003, McGraw-Hill.
110
Factors That Affect Muscle Tension

• Number Coding and Rate Coding
• Length-Tension Relationship
• Force-Velocity Relationship
• Angle of Pull
• Uniarticular vs. Biarticular Muscles
• Cross-sectional Diameter
• Muscle Fiber Type
• Pennation

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Uni Vs. Biarticular Muscles

• Uniarticular muscles
• Ex Brachialis
• Ex Gluteus Maximus

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Uni Vs. Biarticular Muscles

• Biarticular muscles
• May contract cause motion at either one or both
  of its joints
• Advantages over uniarticular muscles

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Advantage 1

• Can cause and/or control motion at more than one
  joint

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Advantage 2

• Can maintain a relatively constant length due to
  "shortening" at one joint and "lengthening" at
  another joint (Quasi-isometric)
• - Recall the Length-Tension Relationship

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Advantage 3

• Prevention of Reciprocal Inhibition
• This effect is negated with biarticular muscles
  when they move concurrently
• Concurrent movement
• Countercurrent movement

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What if the muscles of the hip/knee were
uniarticular?
Hip
Knee
Ankle
Muscles stretched/shortened to extreme lengths!
Implication?
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Figure 20.2, Plowman and Smith (2002). Exercise
Physiology, Benjamin Cummings.
118
Quasi-isometric action? Implication?
Hip
Knee
Ankle
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Active Passive Insufficiency

• Countercurrent muscle actions can reduce the
  effectiveness of the muscle
• As muscle shortens its ability to exert force
  diminishes
• As muscle lengthens its ability to move through
  ROM or generate tension diminishes

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Factors That Affect Muscle Tension

• Number Coding and Rate Coding
• Length-Tension Relationship
• Force-Velocity Relationship
• Angle of Pull
• Uniarticular vs. Biarticular Muscles
• Cross-sectional Diameter
• Muscle Fiber Type
• Pennation

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Cross-Sectional Area

• Hypertrophy vs. hyperplasia
• Increased of myofilaments
• Increased size and of myofibrils
• Increased size of muscle fibers

http//estb.msn.com/i/6B/917B20A6BE353420124115B1A
511C7.jpg
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Factors That Affect Muscle Tension

• Number Coding and Rate Coding
• Length-Tension Relationship
• Force-Velocity Relationship
• Angle of Pull
• Uniarticular vs. Biarticular Muscles
• Cross-sectional Diameter
• Muscle Fiber Type
• Reflexes
• Pennation

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Muscle Fiber Characteristics

• Three basic types
• 1. Type I
• -Slow twitch, oxidative, red
• 2. Type IIb
• -Fast twitch, glycolytic, white
• 3. Type IIa
• -FOG

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Factors That Affect Muscle Tension

• Number Coding and Rate Coding
• Length-Tension Relationship
• Force-Velocity Relationship
• Angle of Pull
• Uniarticular vs. Biarticular Muscles
• Cross-sectional Diameter
• Muscle Fiber Type
• Reflexes
• Pennation

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Effect of Fiber Arrangement on Force Output

• Concept 1 Force directly related to
  cross-sectional area ? more fibers
• Example Thick vs. thin longitudinal/fusiform
  muscle?
• Example Thick fusiform/longitudinal vs. thick
  bipenniform muscle?
• Concept 2 As degree of pennation increases, so
  does of fibers per CSA

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