The Role of Muscles

Applied Kinesiology420:151

Agenda

Introduction to muscles Attachments Structural classification Types of muscle action Factors affecting muscle function Coordination of muscles Types of movements

Introduction to Muscles

Movement occurs via: Internal force External force. Examples?

Introduction to Muscles Properties of skeletal muscle: Extensibility

50% increase Tendons too

Contractility 50% decrease Only muscle

Elasticity Tendons too

Irritability

Agenda

Introduction to muscles Attachments Structural classification Types of muscle action Factors affecting muscle function Coordination of muscles Types of movements

Attachments

How does skeletal muscle attach to bones? Directly? Connective tissue coverings (tendon)

Tendons: Round cord, flat band, aponeurosis Embedded within bone

Attachments

Origin and insertion Tendon length Stability/mobility tendency Proximal/distal tendency

Proximal and distal attachment Less error Example (arm curl vs chin-up)

Attachments

More terms Extremities: Proximal and distal Diaphragm: Peripheral and central Head/Neck/Trunk:

Vertical lines of pull: Upper and lower Horizontal lines of pull: Medial and

lateral

Agenda Introduction to muscles Attachments Structural classification Types of muscle action Factors affecting muscle function Coordination of muscles Types of movements

Structural Classification Fiber arrangement

Longitudinal Quadrate Triangular (radiate) Fusiform Unipenniform Bipenniform Multipenniform

Longitudinal Structure:

Long Strap-like Consistent

diameter Examples:

Sartorius Rectus abdominis

Figure 8.7

Quadrate Structure:

Four-sided Usually flat

Examples: Pronator

quadratus Rhomboid

Figure 3.3

Triangular (Radiate) Structure:

Fibers radiate from narrow to broad attachment

Examples: Pectoralis major Gluteus medius

Figure 3.3

Fusiform Structure:

Rounded Tapered endings

Examples: Biceps brachii Brachialis

Figure 3.3

Unipenniform Pennate Feather Structure:

Series of short parallel fibers

Feather-like arrangement from side of tendon

Examples: Extensor digitorum

longus Tibialis posterior

Figure 3.3

Bipenniform Structure:

Similar to unipenniform

Two sets of fibers Examples:

Flexor hallucis Rectus femoris

Figure 3.3

Multipenniform Structure:

Similar to bipenniform

Multiple tendons Examples:

Middle deltoid

Marieb & Mallet, 2001, Figure 11.3

Effect of Fiber Arrangement on Force Output Concept #1: Force directly related to

cross-sectional area more fibers Example: Thick vs. thin

longitudinal/fusiform muscle? Example: Thick fusiform/longitudinal

vs. thick bipenniform muscle? Concept #2: As degree of pennation

increases, so does # of fibers per CSA

Agenda Introduction to muscles Attachments Structural classification Types of muscle action Factors affecting muscle function Coordination of muscles Types of movements

Types of Muscle Action Contraction vs. action Concentric

Internal > external = + work Eccentric

External > internal = - work Isometric

Internal = external = 0 work Isotonic

Is this really possible? Isokinetic

Agenda Introduction to muscles Attachments Structural classification Types of muscle action Factors affecting muscle function Coordination of muscles Types of movements

Factors Affecting Muscle Function

Line of pull Angle of attachment Length-tension relationship Force-velocity relationship Stored elastic capabilities

Line of Pull The direction of any movement caused

by a muscle is due to: #1: Joint structure

Example: Elbow flexion (biceps brachii) vs. knee extension (rectus femoris)

#2: The relation of the line of pull to the joint Example: Upper fibers pectoralis major as

abductor/adductor

The location of the line of pull in relation to the joint center

determines the movement in this case

Figure 3.4

Angle of Attachment

The angle of attachment affects the efficiency of the movement

Internal forces have two components Rotary force Parallel force

Stabilizing DislocatingParallel forces do not cause movement

therefore reduce efficiency

Stabilizing or dislocating?

Maximum efficiency

Perpendicular

No Parallel Force

Hamill & Knutzen, 2004, Figure 3.23

Hamill & Knutzen, 2004, Figure 3.23

Stabilizing or dislocating? More or less?

Length-Tension Relationship

Optimal length rule Slightly longer than maximum resting length

Too short no force why? Too long no force why?

Passive

Active + Passive

Active

Too short?

Too long?

Figure 3.7

Optimal?

Force-Velocity Relationship

Concentric actions Inversely related Vmax = F0 vice-versa Why? Cross-bridges take time

Eccentric actions Directly related until . . .

Figure 3.8

Stored Elastic Capabilities

Rapid stretch concentric action = more work

Why? Stored elastic energy As speed increases so does effect

Up to a certain point Addition of stretch reflex SSC

Agenda Introduction to muscles Attachments Structural classification Types of muscle action Factors affecting muscle function Coordination of muscles Types of movements

Coordination of Muscles

Role of muscles Biarticular muscles

Role of Muscles Agonists

Directly responsible for movement Synergists

Stabilizers Neutralizers

Antagonists Reciprocal inhibition Braking

Synergists as Stabilizers

Figure 3.9Support of limb Deltoid example

Synergists as Neutralizers

Pectoralis minor and serratus anterior

Biarticular Muscles Proximal/distal attachments cross 2

joints Not long enough for full ROM Result? Tension of one biarticular

muscle transferred to opposite muscle Example: Hamstrings and rectus

femoris Advantage over monoarticular

muscles?Concurrent Movement

Biarticular Muscles

Concurrent vs. countercurrent movements

Maximum ROM Passive/active insufficiency

Agenda Introduction to muscles Attachments Structural classification Types of muscle action Factors affecting muscle function Coordination of muscles Types of movements

Types of Movements Passive

Example: Partner stretch or falling to ground Active:

Slow Constant force = inefficient Rapid Ballistic = efficient

How to stop ballistic movement Antagonist Passive resistance of connective tissue and

eccentric action External object

Review

The muscle fiber (pp. 46-48) Fast vs. slow twitch (pp. 48)