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 CHRONIC ACUTECHRONIC?

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 (°) Torque (Nm) 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 (°) Torque (Nm) 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. F tangential F normal F tangential F normal F tangential F normal

Effects of Other Muscle Force

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

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 z the FMG(s) that is(are) developing force. z the type of muscle action of the FMG(s). z the roles played by the FMG(s). 7. Identify neutralization.

Example 1: Biceps Curl Up PhaseDown Phase Joint Action Motive Force Resistive Force FMG Developing Force Muscle Action Flexion Muscle Weight/Gravity Concentric Elbow Flexors

Example 1: Biceps Curl Up PhaseDown Phase Joint Action Motive Force Resistive Force FMG Developing Force Muscle Action Flexion Muscle Weight/Gravity Concentric Extension Muscle Weight/Gravity Eccentric Elbow Flexors

Example 1: Biceps Curl Up PhaseDown Phase Joint Action Motive Force Resistive Force FMG Developing Force Muscle Action Flexion Muscle Weight/Gravity Concentric Extension Muscle Weight/Gravity Eccentric Elbow Flexors Agonists:FlexorsExtensors

Example 1: Biceps Curl Up PhaseDown Phase Joint Action Motive Force Resistive Force FMG Developing Force Muscle Action Flexion Muscle Weight/Gravity Concentric Extension Muscle Weight/Gravity Eccentric Elbow Flexors Antagonists:ExtensorsFlexors

Stabilization? 1. Rotary stabilization z Wrist flexors 2. Linear stabilization

Neutralization? 1. To prevent scapular or pelvic movement when moving humerus or femur z Shoulder girdle retractors z Shoulder girdle elevators 2. To prevent unwanted motion caused by multijoint muscles z Shoulder extensors z 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.