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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
System Level Structure and Function
General Structure & Function Multiarticular Muscles Muscle Actions Muscle Coordination
System Level Structure and Function
General Structure & Function Multiarticular Muscles Muscle Actions Muscle Coordination
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
CHRONICCHRONIC
ACUTE CHRONIC?ACUTE CHRONIC?
ACUTE CHRONIC?ACUTE CHRONIC?ACUTE CHRONIC?
The Stretch-Shortening Cycle
Lengthening-shortening contraction in which the active muscle is stretched before it shortens
Force & work
Mechanisms
1. time to develop force
2. elastic energy storage in SEC
3. Force potentiation at CB
4. response of stretch reflex
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)
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
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 = 150° JA = 120°MIA = 60 °
JA = 90°MIA = 90 °
JA = 45°MIA = 120 °
JA = 30°MIA = 150 °MIA = 30 °
Understanding Moment Arm Changes Through ROM
JA = 150°MIA = 30 °
JA = 120°MIA = 60 °
JA = 90°MIA = 90 °
JA = 45°MIA = 120 °
JA = 30°MIA = 150 °
Understanding Moment Arm Changes Through ROM
JA = 150°MIA = 30 °
JA = 120°MIA = 60 °
JA = 90°MIA = 90 °
JA = 45°MIA = 120 °
JA = 30°MIA = 150 °
Understanding Rotational Effects Through ROM
JA = 150°MIA = 30 °
JA = 120°MIA = 60 °
JA = 90°MIA = 90 °
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
Muscle Force for Joint Stability
Joint stability for injury prevention determined by linear effects of muscle pull.
Understanding Linear Effects Through ROM
JA = 150°MIA = 30 °
JA = 120°MIA = 60 ° JA = 90°
MIA = 90 °
System Level Stabilization Function
Stabilization role varies with MIA Bony structure Other muscle forces External forces
Effects of Bony Structure
Source: Mediclip. (1995). Baltimore: Williams & Wilkins.
Ftangential
Fnormal
Ftangential
Fnormal
Ftangential
Fnormal
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?
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.
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
System Level Structure and Function
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 one-joint
3. Redistributes power & torque throughout limb
Disadvantages
1. Active insufficiency
2. Passive insufficiency
System Level Structure and Function
General Structure & Function Multiarticular Muscles Muscle Actions Muscle Coordination
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
Concentric
Shortens to cause movement Rotational movement Mechanically:
Net Muscle (Motive) Torque > Net Resistive Torque
Eccentric
Lengthens to resist, control, or slow down movement
Rotational movement Mechanically:
Net Muscle (Resistive) Torque < Net Motive Torque
Isometric
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
Resulting motion dependent on all torques acting about the joint (net torque)
Isometric?Eccentric?Conditions for concentric?
Influence of Gravity & Speed
Downward (with gravity) Upward (opposing gravity) Horizontal (perpendicular
to gravity)
Consider direction & speed of movement relative to gravity
System Level Structure and Function
General Structure & Function Multiarticular Muscles Muscle Actions Muscle Coordination
Agonist (Mover)
The role played by a muscle acting to cause a movement Prime movers Assistant movers Arbitrary distinction
Force development during concentric action Relaxation during eccentric action
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
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
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
The Muscular System
1. Organ Level Structure & Function
2. System Level Structure & Function
3. Injury to the Musculoskeletal System
4. Muscular Analysis
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?
To perform a muscular analysis (ID muscle actions and responsible groups):
5. Identify whether there are joints/bones that must be stabilized.
6. 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).
7. Identify neutralization.
Example 1: Biceps CurlUp Phase Down Phase
Joint Action
Motive Force
Resistive Force
FMG Developing Force
Muscle Action
Flexion
Muscle
Weight/Gravity
Concentric
Elbow Flexors
Example 1: Biceps CurlUp Phase Down Phase
Joint Action
Motive Force
Resistive Force
FMG Developing Force
Muscle Action
Flexion
Muscle
Weight/Gravity
Concentric
Extension
Muscle
Weight/Gravity
Eccentric
Elbow FlexorsElbow Flexors
Example 1: Biceps CurlUp Phase Down Phase
Joint Action
Motive Force
Resistive Force
FMG Developing Force
Muscle Action
Flexion
Muscle
Weight/Gravity
Concentric
Extension
Muscle
Weight/Gravity
Eccentric
Elbow FlexorsElbow Flexors
Agonists: Flexors Extensors
Example 1: Biceps CurlUp Phase Down Phase
Joint Action
Motive Force
Resistive Force
FMG Developing Force
Muscle Action
Flexion
Muscle
Weight/Gravity
Concentric
Extension
Muscle
Weight/Gravity
Eccentric
Elbow FlexorsElbow Flexors
Antagonists: Extensors Flexors
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. To prevent scapular movement during elevation of the humerus
4. Other? Biceps brachii – shoulder flexion, RU supination Brachialis – none Brachioradialis – RU motion Pronator teres – RU pronation
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.