Download Introduction to the Skeletal System

The Muscular System
1.
2.
3.
4.
Organ Level Structure & Function
System Level Structure & Function
Injury to the Musculoskeletal System
Muscular Analysis
System Level Structure and
Function
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General Structure & Function
Multiarticular Muscles
Muscle Actions
Muscle Coordination
System Level Structure and
Function
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General Structure & Function
Multiarticular Muscles
Muscle Actions
Muscle Coordination
Simple
Joint
System
General System Level Function
Force & Torque
Production
(for stabilization and/or movement)
Factors that Affect Force
Output

Physiological factors
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CHRONIC
CHRONIC
Neurological factors
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Cross-sectional area
Fiber type
Muscle fiber activation
Rate of motor unit activation
ACUTE CHRONIC?
ACUTE CHRONIC?
Biomechanical factors
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Muscle architecture
Length-tension relationship
Force-velocity relationship
ACUTE CHRONIC?
ACUTE CHRONIC?
ACUTE CHRONIC?
The Stretch-Shortening Cycle
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
Lengthening-shortening
contraction in which the
active muscle is
stretched before it
shortens
 Force & work
1.
2.
3.
4.
Mechanisms
 time to develop force
 elastic energy
storage in SEC
Force potentiation at
CB
 response of stretch
reflex
Reflex Control – The Reflex Arc
Reflex Control – Stretch Reflex
Mobility Determined by Torque
Output
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Factors that Affect Torque Output
Force
Moment arm
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Point of force application (attachment site)
Angle of force application (muscle insertion
angle)
Muscle Attachments
1.
2.
3.
4.
Further from joint is better (theoretically)
Structural constraints negate #1
Cannot alter attachment sites
Strength differences due, in part, to
attachment differences
Muscle Insertion Angle
1. 90 is better
2. MIA typically < 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
Understanding Moment Arm Changes Through
ROM
JA = 90°
MIA = 90 °
JA = 150° JA = 120°
MIA = 30 ° MIA = 60 °
JA = 45°
MIA = 120 °
JA = 30°
MIA = 150 °
Understanding Moment Arm Changes Through
ROM
JA = 90°
MIA = 90 °
JA = 150° JA = 120°
MIA = 30 ° MIA = 60 °
JA = 45°
MIA = 120 °
JA = 30°
MIA = 150 °
Understanding Moment Arm Changes Through
ROM
JA = 90°
MIA = 90 °
JA = 150° JA = 120°
MIA = 30 ° MIA = 60 °
JA = 45°
MIA = 120 °
JA = 30°
MIA = 150 °
Torque (Nm)
Biceps Brachii Strength
0
90
Joint Angle (°)
180
JA = 120°
MIA = 60 °
JA = 150°
MIA = 30 °
JA = 90°
MIA = 90 °
Understanding Rotational Effects
Through ROM
JA = 45°
MIA = 120 °
JA = 30°
MIA = 150 °
Understanding Rotational Effects
Through ROM
JA = 90°
MIA = 20°
JA = 120°
MIA = 20°
JA = 150°
MIA = 20°
JA = 45°
MIA = 20°
JA = 30°
MIA = 20°
Torque (Nm)
Brachioradialis Strength
0
90
Joint Angle (°)
180
Summary of System Level
Rotational Function
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Torque output varies across ROM
Variation depends on:



Force-length changes
Moment arm changes
Variation differs across muscles & joints
Muscle Force for Joint Stability
Joint stability for injury prevention
determined by linear effects of muscle
pull.
JA = 120°
MIA = 60 °
JA = 150°
MIA = 30 °
JA = 90°
MIA = 90 °
Understanding Linear Effects
Through ROM
JA = 45°
MIA = 120 °
JA = 30°
MIA = 150 °
Understanding Linear Effects
Through ROM
JA = 90°
MIA = 20°
JA = 120°
MIA = 20°
JA = 150°
MIA = 20°
JA = 45°
MIA = 20°
JA = 30°
MIA = 20°
System Level Stabilization
Function
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Stabilization role varies with
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MIA
Bony structure
Other muscle forces
External forces
Effects of Bony Structure
Fnormal
Ftangential
Fnormal
Ftangential
Fnormal
Ftangential
Source: Mediclip. (1995). Baltimore: Williams & Wilkins.
Effects of Other
Muscle Force
Effects of External Forces
Effects of External Forces
System Level Function:
Key Relationships
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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?
General Structure & Function:
Summary
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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.
General Structure & Function:
Summary
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
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
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Bony structure
Other muscle forces
External forces
System Level Structure and
Function
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General Structure & Function
Multiarticular Muscles
Muscle Actions
Muscle Coordination
Multiarticular Muscles
Advantages
1. Couples the motion at
multiple joints
2.  shortening velocity
as compared to onejoint
3. Redistributes power &
torque throughout limb
Disadvantages
1. Active insufficiency
2. Passive insufficiency
Active
insufficiency
Active Insufficiency
Active Insufficiency
Passive Insufficiency
System Level Structure and
Function
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General Structure & Function
Multiarticular Muscles
Muscle Actions
Muscle Coordination
Related Terminology
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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
Types of Muscle Actions
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Concentric
Eccentric
Isometric
Concentric
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Shortens to cause movement
Rotational movement
Mechanically:
Net Muscle (Motive) Torque > Net Resistive Torque
Eccentric
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Lengthens to resist, control, or slow down
movement
Rotational movement
Mechanically:
Net Muscle (Resistive) Torque < Net Motive Torque
Isometric
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Stays the same so that bone will stay fixed
No movement
Mechanically:
Net Muscle Torque = Other Torque
Total Net Torque = 0
System Level:
Muscle Actions
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Resulting
motion
dependent on
all torques
acting about
the joint (net
torque)
Conditions for concentric?
Eccentric?
Isometric?
Influence of Gravity & Speed
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Downward (with gravity)
Upward (opposing gravity)
Horizontal (perpendicular
to gravity)
Consider direction & speed
of movement relative to
gravity
System Level Structure and
Function

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General Structure & Function
Multiarticular Muscles
Muscle Actions
Muscle Coordination
Muscle Coordination:
Roles that Muscles Play
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Agonists
Antagonists
Stabilizers
Neutralizers
Agonist (Mover)
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The role played by a muscle acting to cause
a movement
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Prime movers
Assistant movers
Arbitrary distinction
 Force development during concentric action
 Relaxation during eccentric action
Antagonist
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The role played by a muscle acting
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Force development during eccentric action
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to control movement of a body segment against some
other non-muscle force
to slow or stop a movement
Check ballistic movements
Relaxation during concentric action
Stabilizer

The role played by a muscle to stabilize
(fixate) a body part against some other force
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rotary (joint) stabilizer
linear (bone) stabilizer
Isometric muscle action
Neutralizer
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The role played by a muscle to eliminate an
unwanted action produced by an agonist
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Scapular or pelvic stabilization
Multijoint muscles
Elevation of the humerus
Muscle action varies
Cocontraction

The simultaneous contraction of movers and
antagonists
The Muscular System
1.
2.
3.
4.
Organ Level Structure & Function
System Level Structure & Function
Injury to the Musculoskeletal System
Muscular Analysis
To perform a muscular analysis:
1.
2.
3.
4.
Break the skill into phases.
Determine the joint action.
Determine the motive force – muscle or
some other force?
Determine the resistive force – muscle or
some other force?
To perform a muscular analysis (ID muscle
actions and responsible groups):
5.
6.
Identify whether there are joints/bones that
must be stabilized.
Identify
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7.
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.
Example 1: Biceps Curl
Up Phase
Joint Action
Flexion
Motive Force
Muscle
Resistive
Force
Weight/Gravity
FMG
Developing
Force
Muscle Action
Elbow Flexors
Concentric
Down Phase
Example 1: Biceps Curl
Up Phase
Down Phase
Joint Action
Flexion
Extension
Motive Force
Muscle
Weight/Gravity
Resistive
Force
Weight/Gravity Muscle
FMG
Developing
Force
Muscle Action
Elbow Flexors
Elbow Flexors
Concentric
Eccentric
Agonists:
Flexors
Extensors
Example 1: Biceps Curl
Up Phase
Down Phase
Joint Action
Flexion
Extension
Motive Force
Muscle
Weight/Gravity
Resistive
Force
Weight/Gravity Muscle
FMG
Developing
Force
Muscle Action
Elbow Flexors
Elbow Flexors
Concentric
Eccentric
Antagonists:
Extensors
Flexors
Example 1: Biceps Curl
Up Phase
Down Phase
Joint Action
Flexion
Extension
Motive Force
Muscle
Weight/Gravity
Resistive
Force
Weight/Gravity Muscle
FMG
Developing
Force
Muscle Action
Elbow Flexors
Elbow Flexors
Concentric
Eccentric
Stabilization?
1.
Rotary stabilization

2.
Wrist flexors
Linear stabilization
Neutralization?
1.
To prevent scapular or pelvic movement
when moving humerus or femur
 Shoulder
girdle retractors
 Shoulder girdle elevators
2.
To prevent unwanted motion caused by
multijoint muscles
 Shoulder
extensors
 Forearm pronators
Neutralization
3.
4.
To prevent scapular movement during
elevation of the humerus
Other?
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Biceps brachii – shoulder flexion, RU supination
Brachialis – none
Brachioradialis – RU motion
Pronator teres – RU pronation
Summary
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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.
Summary
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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.