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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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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

Simple Joint System

General System Level Function

Force & Torque Production

(for stabilization and/or movement)

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

Reflex Control – The Reflex Arc

Reflex Control – 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 °

Biceps Brachii Strength

Joint Angle (°)

Tor

que

(Nm

)

0 90 180

Joint Angle

Understanding Rotational Effects Through ROM

JA = 150°MIA = 30 °

JA = 120°MIA = 60 °

JA = 90°MIA = 90 °

Understanding Rotational Effects Through ROM

JA = 45°MIA = 120 °

JA = 30°MIA = 150 °

JA = 150°MIA = 20°

JA = 120°MIA = 20°

JA = 90°MIA = 20°

JA = 45°MIA = 20°

JA = 30°MIA = 20°

Brachioradialis Strength

Joint Angle (°)

Tor

que

(Nm

)

0 90 180

Joint Angle

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 °

Understanding Linear Effects Through ROM

JA = 45°MIA = 120 °

JA = 30°MIA = 150 °

JA = 150°MIA = 20°

JA = 120°MIA = 20°

JA = 90°MIA = 20°

JA = 45°MIA = 20°

JA = 30°MIA = 20°

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

Effects of Other Muscle Force

Effects of External Forces

Effects of External Forces

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

Active insufficiency

Active Insufficiency

Active Insufficiency

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

Types of Muscle Actions

Concentric Eccentric Isometric

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

Muscle Coordination: Roles that Muscles Play

Agonists Antagonists Stabilizers Neutralizers

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

Cocontraction

The simultaneous contraction of movers and antagonists

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

Stabilization?

1. Rotary stabilization Wrist flexors

2. 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. 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.

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.