The Muscular System

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The Muscular System

1. Organ Level Structure Function
2. System Level Structure Function
3. Injury to the Musculoskeletal System
4. Muscular Analysis

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System Level Structure and Function

• General Structure Function
• Multiarticular Muscles
• Muscle Actions
• Muscle Coordination

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System Level Structure and Function

• General Structure Function
• Multiarticular Muscles
• Muscle Actions
• Muscle Coordination

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Simple Joint System
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General System Level Function

• Force Torque
• Production
• (for stabilization and/or movement)

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Factors that Affect Force Output

• Physiological factors
• Cross-sectional area
• Fiber type
• Neurological factors
• Muscle fiber activation
• Rate of motor unit activation
• Biomechanical factors
• Muscle architecture
• Length-tension relationship
• Force-velocity relationship

CHRONIC CHRONIC ACUTE CHRONIC? ACUTE CHRONIC?
ACUTE CHRONIC? ACUTE CHRONIC? ACUTE CHRONIC?
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The Stretch-Shortening Cycle

• Lengthening-shortening contraction in which the
  active muscle is stretched before it shortens
• ? Force work

• Mechanisms
• ? time to develop force
• ? elastic energy storage in SEC
• Force potentiation at CB
• ? response of stretch reflex

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Reflex Control The Reflex Arc
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Reflex Control Stretch Reflex
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Mobility Determined by Torque Output

• Factors that Affect Torque Output
• Force
• Moment arm
• Point of force application (attachment site)
• Angle of force application (muscle insertion
  angle)

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Muscle Attachments

1. Further from joint is better (theoretically)
2. Structural constraints negate 1
3. Cannot alter attachment sites
4. Strength differences due, in part, to attachment
   differences

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Muscle Insertion Angle

1. 90? is better
2. MIA typically lt 45
3. MIA not constant through joint ROM, affecting
   strength through ROM
4. Cannot alter MIA
5. Strength differences due, in part, to MIA
   differences

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Understanding Moment Arm Changes Through ROM
JA 90 MIA 90
JA 45 MIA 120
JA 30 MIA 150
JA 150
JA 120 MIA 60
MIA 30
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Understanding Moment Arm Changes Through ROM
JA 90 MIA 90
JA 45 MIA 120
JA 30 MIA 150
JA 150 MIA 30
JA 120 MIA 60
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Understanding Moment Arm Changes Through ROM
JA 90 MIA 90
JA 45 MIA 120
JA 30 MIA 150
JA 150 MIA 30
JA 120 MIA 60
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Biceps Brachii Strength
Torque (Nm)
0 90
180
Joint Angle ()
Joint Angle
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JA 90 MIA 90
JA 120 MIA 60
JA 150 MIA 30
Understanding Rotational Effects Through ROM
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JA 30 MIA 150
JA 45 MIA 120
Understanding Rotational Effects Through ROM
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JA 90 MIA 20
JA 120 MIA 20
JA 150 MIA 20
JA 45 MIA 20
JA 30 MIA 20
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Brachioradialis Strength
Torque (Nm)
0 90
180
Joint Angle ()
Joint Angle
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Summary of System Level Rotational Function

• Torque output varies across ROM
• Variation depends on
• Force-length changes
• Moment arm changes
• Variation differs across muscles joints

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Muscle Force for Joint Stability

• Joint stability for injury prevention determined
  by linear effects of muscle pull.

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JA 120 MIA 60
JA 90 MIA 90
JA 150 MIA 30
Understanding Linear Effects Through ROM
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JA 30 MIA 150
JA 45 MIA 120
Understanding Linear Effects Through ROM
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JA 90 MIA 20
JA 120 MIA 20
JA 150 MIA 20
JA 45 MIA 20
JA 30 MIA 20
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System Level Stabilization Function

• Stabilization role varies with
• MIA
• Bony structure
• Other muscle forces
• External forces

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Effects of Bony Structure
Fnormal
Ftangential
Fnormal
Ftangential
Fnormal
Source Mediclip. (1995). Baltimore Williams
Wilkins.
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Effects of Other Muscle Force
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Effects of External Forces
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Effects of External Forces
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System Level Function Key Relationships

• What is the relationship between MIA moment arm
  (MA)?
• What is the relationship between MIA JA?
• What is the relationship between JA MA?
• What is the role of the normal component?
• What is the relationship between the normal
  component and the MIA?
• What is the role of the tangential component?
• What is the relationship between the tangential
  component and the MIA?

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General Structure Function Summary

• Torque output of muscle is affected by anything
  that affects moment arm or force output of muscle
  organ.
• Acute changes in torque through ROM dependent on
  force-length MIA changes.
• Chronic changes in muscle torque dependent on
  training effects on physiological, neural, and
  biomechanical factors that affect force.

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General Structure Function Summary

• Muscle force for stabilization function
  determined by physiological, neural, and
  biomechanical factors that affect force as well
  as MIA.
• Stabilization function defined by presence of
• Bony structure
• Other muscle forces
• External forces

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System Level Structure and Function

• General Structure Function
• Multiarticular Muscles
• Muscle Actions
• Muscle Coordination

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Multiarticular Muscles

• Advantages
• Couples the motion at multiple joints
• ? shortening velocity as compared to one-joint
• Redistributes power torque throughout limb

• Disadvantages
• Active insufficiency
• Passive insufficiency

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Active insufficiency
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Active Insufficiency
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Active Insufficiency
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Passive Insufficiency
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System Level Structure and Function

• General Structure Function
• Multiarticular Muscles
• Muscle Actions
• Muscle Coordination

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Related Terminology

• muscle action the development of tension
  (force) by a muscle
• functional muscle group a group of muscles that
  are capable of causing a specific joint action
  (e.g., wrist radial deviators)
• motive force (or torque) force causing the
  observed movement
• resistive force (or torque) force opposing the
  observed movement

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Types of Muscle Actions

• Concentric
• Eccentric
• Isometric

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Concentric

• Shortens to cause movement
• Rotational movement
• Mechanically
• Net Muscle (Motive) Torque gt Net Resistive Torque

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Eccentric

• Lengthens to resist, control, or slow down
  movement
• Rotational movement
• Mechanically
• Net Muscle (Resistive) Torque lt Net Motive Torque

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Isometric

• Stays the same so that bone will stay fixed
• No movement
• Mechanically
• Net Muscle Torque Other Torque
• Total Net Torque 0

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System Level Muscle Actions

• Resulting motion dependent on all torques acting
  about the joint (net torque)

Isometric?
Eccentric?
Conditions for concentric?
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Influence of Gravity Speed

• Downward (with gravity)
• Upward (opposing gravity)
• Horizontal (perpendicular to gravity)
• Consider direction speed of movement relative
  to gravity

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System Level Structure and Function

• General Structure Function
• Multiarticular Muscles
• Muscle Actions
• Muscle Coordination

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Muscle Coordination Roles that Muscles Play

• Agonists
• Antagonists
• Stabilizers
• Neutralizers

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Agonist (Mover)

• The role played by a muscle acting to cause a
  movement
• Prime movers
• Assistant movers

• Force development during concentric action
• Relaxation during eccentric action

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Antagonist

• The role played by a muscle acting
• to control movement of a body segment against
  some other non-muscle force
• to slow or stop a movement
• Force development during eccentric action
• Check ballistic movements
• Relaxation during concentric action

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Stabilizer

• The role played by a muscle to stabilize (fixate)
  a body part against some other force
• rotary (joint) stabilizer
• linear (bone) stabilizer
• Isometric muscle action

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Neutralizer

• The role played by a muscle to eliminate an
  unwanted action produced by an agonist
• Scapular or pelvic stabilization
• Multijoint muscles
• Elevation of the humerus
• Muscle action varies

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Cocontraction

• The simultaneous contraction of movers and
  antagonists

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The Muscular System

1. Organ Level Structure Function
2. System Level Structure Function
3. Injury to the Musculoskeletal System
4. Muscular Analysis

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To perform a muscular analysis

1. Break the skill into phases.
2. Determine the joint action.
3. Determine the motive force muscle or some other
   force?
4. Determine the resistive force muscle or some
   other force?

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To perform a muscular analysis (ID muscle actions
and responsible groups)

• Identify whether there are joints/bones that must
  be stabilized.
• Identify
• the FMG(s) that is(are) developing force .
• the type of muscle action of the FMG(s).
• the roles played by the FMG(s).
• Identify neutralization.

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Example 1 Biceps Curl
Up Phase Down Phase
Joint Action
Motive Force
Resistive Force
FMG Developing Force
Muscle Action
Flexion
Muscle
Weight/Gravity
Elbow Flexors
Concentric
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Example 1 Biceps Curl
Up Phase Down Phase
Joint Action
Motive Force
Resistive Force
FMG Developing Force
Muscle Action
Flexion
Extension
Weight/Gravity
Muscle
Muscle
Weight/Gravity
Elbow Flexors
Elbow Flexors
Concentric
Eccentric
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Example 1 Biceps Curl
Agonists
Flexors Extensors
Up Phase Down Phase
Joint Action
Motive Force
Resistive Force
FMG Developing Force
Muscle Action
Flexion
Extension
Weight/Gravity
Muscle
Muscle
Weight/Gravity
Elbow Flexors
Elbow Flexors
Concentric
Eccentric
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Example 1 Biceps Curl
Antagonists
Extensors Flexors
Up Phase Down Phase
Joint Action
Motive Force
Resistive Force
FMG Developing Force
Muscle Action
Flexion
Extension
Weight/Gravity
Muscle
Muscle
Weight/Gravity
Elbow Flexors
Elbow Flexors
Concentric
Eccentric
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Stabilization?

• Rotary stabilization
• Wrist flexors
• Linear stabilization

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Neutralization?

• To prevent scapular or pelvic movement when
  moving humerus or femur
• Shoulder girdle retractors
• Shoulder girdle elevators
• To prevent unwanted motion caused by multijoint
  muscles
• Shoulder extensors
• Forearm pronators

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Neutralization

• To prevent scapular movement during elevation of
  the humerus
• Other?
• Biceps brachii shoulder flexion, RU supination
• Brachialis none
• Brachioradialis RU motion
• Pronator teres RU pronation

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Summary

• Movement at a single joint is possible because of
  the complex coordination that occurs between
  numerous muscles.
• Therefore, all those muscles must have adequate
  strength to accomplish its task in a given
  movement.
• Injury to or lack of strength in any of those
  muscles can result in the inability to perform
  the movement.

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Summary

• A muscular analysis allows us to identify the
  muscles that contribute to a movement and how
  they contribute to the movement.
• We can then prepare conditioning rehabilitation
  programs that target utilized muscles
  appropriately.