Neuromuscular Fundamentals

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Neuromuscular Fundamentals

• Anatomy and Physiology of Human Movement
• 420050

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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
• Protection
• Posture and support
• Produce a major portion of total body heat
• 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 - muscles work in groups
  rather than independently to achieve a given
  joint motion

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Muscle Tissue Properties

• Irritability or Excitability - property of muscle
  being sensitive or responsive to chemical,
  electrical, or mechanical stimuli
• Contractility - ability of muscle to contract
  develop tension or internal force against
  resistance when stimulated
• Extensibility - ability of muscle to be passively
  stretched beyond it normal resting length
• Elasticity - ability of muscle to return to its
  original length following stretching

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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 Receptor sites
• Cell body Integration
• Axon Transmission
• Myelin sheath Protection and speed
• Nodes of Ranvier Saltatory conduction
• Terminal branches Increased innervation
• Axon terminals Connection with muscular system
• Synaptic vescicles Delivery mechanism of
  message
• Neurotransmitter The message

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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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Skeletal Muscle Properties

• Extensibility The ability to lengthen
• Contractility The ability to shorten
• Elasticity The ability to return to original
  length
• Irritability The ability to receive and respond
  to stimulus

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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.
21
http//staff.fcps.net/cverdecc/Adv20AP/Notes/Mus
cle20Unit/sliding20filament20theory/slidin16.jp
g
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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
• Muscles ability to exert force
• Range through which it can effectively exert
  force onto the bones

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Shape of Muscles Fiber Arrangement

• Two major types of fiber arrangements
• Parallel pennate
• Each is further subdivided according to shape

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Fiber Arrangement - Parallel

• Parallel muscles
• fibers arranged parallel to length of muscle
• produce a greater range of movement than similar
  sized muscles with pennate arrangement
• Categorized into following shapes
• Flat
• Fusiform
• Strap
• Radiate
• Sphincter or circular

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Fiber Arrangement - Parallel

• Flat muscles
• Usually thin broad, originating from broad,
  fibrous, sheet-like aponeuroses
• Allows them to spread their forces over a broad
  area
• Ex Rectus abdominus external oblique

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

• Fusiform muscles
• Spindle-shaped with a central belly that tapers
  to tendons on each end
• Allows them to focus their power onto small, bony
  targets
• Ex Brachialis, biceps brachii

Figure 3.3. Hamilton, Weimar Luttgens (2005).
Kinesiology Scientific basis for human motion.
McGraw-Hill.
58
Fiber Arrangement - Parallel

• Strap muscles
• More uniform in diameter with essentially all
  fibers arranged in a long parallel manner
• Enables a focusing of power onto small, bony
  targets
• Ex Sartorius, sternocleidomastoid

Figure 8.7. Hamilton, Weimar Luttgens (2005).
Kinesiology Scientific basis for human motion.
McGraw-Hill.
59
Fiber Arrangement - Parallel

• Radiate muscles
• Also described sometimes as being triangular,
  fan-shaped or convergent
• Have combined arrangement of flat fusiform
• Originate on broad aponeuroses converge onto a
  tendon
• Ex Pectoralis major, trapezius

Modified from Van De Graaff KM Human anatomy, ed
6, Dubuque, IA, 2002, McGraw-Hill.
60
Fiber Arrangement - Parallel

• Sphincter or circular muscles
• Technically endless strap muscles
• Surround openings function to close them upon
  contraction
• Ex Orbicularis oris surrounding the mouth

Modified from Van De Graaff KM Human anatomy, ed
6, Dubuque, IA, 2002, McGraw-Hill.
61
Fiber Arrangement - Pennate

• Pennate muscles
• Have shorter fibers
• Arranged obliquely to their tendons in a manner
  similar to a feather
• Reduces mechanical efficiency of each fiber
• Increases overall number of fibers packed into
  muscle
• Overall effect more crossbridges more force!

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Fiber Arrangement - Pennate

• Categorized based upon the exact arrangement
  between fibers tendon
• Unipennate
• Bipennate
• Multipennate

Modified from Van De Graaff KM Human anatomy, ed
6, Dubuque, IA, 2002, McGraw-Hill.
63
Fiber Arrangement - Pennate

• Unipennate muscles
• Fibers run obliquely from a tendon on one side
  only
• Ex Biceps femoris, extensor digitorum longus,
  tibialis posterior

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Fiber Arrangement - Pennate

• Bipennate muscle
• Fibers run obliquely on both sides from a central
  tendon
• Ex Rectus femoris, flexor hallucis longus

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Fiber Arrangement - Pennate

• Multipennate muscles
• Have several tendons with fibers running
  diagonally between them
• Ex Deltoid
• 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)
• Structurally, the proximal attachment of a muscle
  or the part that attaches closest to the midline
  or center of the body
• Functionally historically, the least movable
  part or attachment of the muscle
• Note The least movable may not necessarily be
  the proximal attachment

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Muscle Actions Terminology

• Insertion (Distal Attachment)
• Structurally, the distal attachment or the part
  that attaches farthest from the midline or center
  of the body
• Functionally historically, the most movable
  part is generally considered the insertion

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Muscle Actions Terminology

• When a particular muscle is activated
• It tends to pull both ends toward the center
• Actual movement is towards more stable attachment
• Examples
• Bicep curl vs. chin-up
• Hip extension vs. RDL

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Muscle Actions

• Action - when tension is developed in a muscle as
  a result of a stimulus
• Muscle contraction term is exclusive in nature
• As a result, it has become increasingly common to
  refer to the various types of muscle contractions
  as muscle actions instead

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Muscle Actions

• Muscle actions can be used to cause, control, or
  prevent joint movement or
• To initiate or accelerate movement of a body
  segment
• To slow down or decelerate movement of a body
  segment
• To prevent movement of a body segment by external
  forces

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Types of Muscle Actions

• Muscle action (under tension)
• Isometric
• Isotonic
• Concentric
• Eccentric

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Types of Muscle Actions

• Isometric action
• Tension is developed within muscle but joint
  angles remain constant
• AKA Static movement
• May be used to prevent a body segment from being
  moved by external forces
• Internal torque external torque

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Types of Muscle Actions

• Isotonic (same tension) contractions involve
  muscle developing tension to either cause or
  control joint movement
• AKA Dynamic movement
• 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
• Internal torque gt external torque
• Causes movement against gravity or other
  resistance
• Described as being a positive action
• Eccentric contractions involve the muscle
  lengthening under tension
• External torque gt internal torque
• Controls movement caused by gravity or other
  resistance
• Described as being a negative action

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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

• Movement may occur at any given joint without any
  muscle contraction whatsoever
• referred to as passive
• solely due to external forces such as those
  applied by another person, object, or resistance
  or the force of gravity in the presence of muscle
  relaxation

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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
• The activated muscle group during concentric or
  eccentric phases of movement
• Known as primary or prime movers, or muscles most
  involved

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Role of Muscles

• Antagonist muscles
• Located on opposite side of joint from agonist
• Have the opposite concentric action
• Also known as contralateral muscles
• Work in cooperation with agonist muscles by
  relaxing allowing movement
• Reciprocal Inhibition

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Role of Muscles

• Stabilizers
• Surround joint or body part
• Contract to fixate or stabilize the area to
  enable another limb or body segment to exert
  force move
• Also known as fixators

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Role of Muscles

• Synergist
• Assist in action of agonists
• Not necessarily prime movers for the action
• Also known as guiding muscles
• Assist in refined movement rule out undesired
  motions

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Role of Muscles

• Neutralizers
• Counteract or neutralize the action of another
  muscle to prevent undesirable movements such as
  inappropriate muscle substitutions
• Activation to resist specific actions of other
  muscles

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Outline

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

86
Factors That Affect Muscle Tension

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

87
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
• Activating those motor units containing a greater
  number of muscle fibers (Number Coding)
• Activating more motor units (Number Coding)
• Increasing the frequency of motor unit activation
  (Rate Coding)

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Number Coding Rate Coding

• Number of muscle fibers per motor unit varies
  significantly
• From less than 10 in muscles requiring precise
  and detailed such as muscles of the eye
• To as many as a few thousand in large muscles
  that perform less complex activities such as the
  quadriceps and gastrocnemius

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Number Coding Rate Coding

• Greater contraction forces may also be achieved
  by increasing the frequency or motor unit
  activation (Rate Coding)

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All or None Principle

• Motor unit
• Single motor neuron all muscle fibers it
  innervates
• Typical muscle contraction
• The number of motor units responding (and number
  of muscle fibers contracting) within the muscle
  may vary significantly from relatively few to
  virtually all
• All of the fibers within the motor unit will fire
  when stimulated by the CNS
• All or None Principle - regardless of number,
  individual muscle fibers within a given motor
  unit will either fire contract maximally or not
  at all

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Factors That Affect Muscle Tension

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

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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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Figure 20.2, Plowman and Smith (2002). Exercise
Physiology, Benjamin Cummings.
94
Factors That Affect Muscle Tension

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

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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, the muscle
  begins eccentric action
• As load increases, eccentric velocity increases
• Eventually velocity maximum when muscle tension
  fails

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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
• Uniarticular vs. Biarticular Muscles
• Cross-sectional Diameter
• Muscle Fiber Type

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Uni Vs. Biarticular Muscles

• Uniarticular muscles
• Cross act directly only on the single joint
  that they cross
• Ex Brachialis
• Can only pull humerus ulna closer together
• Ex Gluteus Maximus
• Can only pull posterior femur and pelvis closer
  together

101
Uni Vs. Biarticular Muscles

• Biarticular muscles
• Cross act on two different joints
• 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
• Rectus femoris Knee extension, hip flexion
• Hamstrings Knee flexion, hip extension

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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
• Concurrent lengthening and shortening of
  muscle
• Countercurrent movement
• Both ends lengthen or shorten

105
What if the muscles of the hip/knee were
uniarticular?
Hip
Knee
Ankle
Muscles stretched/shortened to extreme lengths!
Implication?
106
Figure 20.2, Plowman and Smith (2002). Exercise
Physiology, Benjamin Cummings.
107
Quasi-isometric action? Implication?
Hip
Knee
Ankle
108
Active Passive Insufficiency

• Countercurrent muscle actions can reduce the
  effectiveness of the muscle
• As muscle shortens its ability to exert force
  diminishes
• Active insufficiency Diminished crossbridges
• As muscle lengthens its ability to move through
  ROM or generate tension diminishes
• Passively insufficiency Diminished crossbridges
  and excessive passive tension

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Factors That Affect Muscle Tension

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

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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
111
Factors That Affect Muscle Tension

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

112
Muscle Fiber Characteristics

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