7 - Myology

Myology Overview

  • Course Title: KINS 1120

  • Instructor: Raelene Lang

  • Institution: Langara College of Higher Learning

Learning Objectives

  • Discuss muscle naming conventions with examples.

  • Describe muscle contraction through sliding filament theory.

  • Explain the impact of pennation on muscle contraction.

  • Define general muscle categories (e.g., agonist, synergist).

  • Understand the length-tension relationship of muscle.

  • Compare and contrast muscle fiber types.

  • Discuss how fiber distribution influences athletic performance.

  • Explain motor unit activation principles (all-or-none, size, gradation of force).

  • Compare relative force, velocity, and power during muscle contractions.

Importance of Understanding Anatomy

  • Essential for efficient training.

  • Aids comprehension of human movement.

  • Helps identify which muscles produce specific movements.

  • Assists in recognizing faulty movement patterns for safer program development.

    • Example: Knee pain or lack of range of motion.

  • SAID Principle: Specific Adaptations to Imposed Demands; specific adaptations require corresponding stressors.

Muscle Nomenclature

Based on Shape

  • Common muscle names based on shape include:

    • Deltoideus

    • Rectus Abdominis

    • Rhomboideus Major

    • Trapezius

    • Latissimus Dorsi

Based on Size

  • Size nomenclature examples:

    • Gluteus Maximus

    • Pectoralis Major

    • Peroneus Brevis

    • Gluteus Minimus

    • Longissimus Thoracics

    • Vastus Lateralis

Based on Number of Attachments

  • Examples:

    • Biceps Femoris (two attachments)

    • Triceps Brachii (three attachments)

    • Quadriceps (four attachments)

Based on Depth

  • Examples:

    • Flexor Digitorum Superficialis (superficial attachment)

    • Obliquus Internus Abdominis

Based on Position

  • Position nomenclature includes:

    • Tibialis Anterior

    • Infraspinatus

    • Vastus Medialis

Based on Function

  • Examples of function types:

    • Flexor Carpi Radialis

    • Pronator Teres

    • Supinator

    • Adductor Magnus

Muscle Microstructure

  • Skeletal Muscle Structure

    • Composed of muscle tissue, connective tissue, nerves, and blood vessels.

    • Epimysium: Outer fibrous connective tissue layer contiguous with tendons.

    • Muscle fibers grouped into bundles (fasciculi) surrounded by Perimysium (CT surrounding fasciculi).

    • Endomysium: CT surrounding individual muscle fibers.

    • Sarcoplasm: Contains proteins, glycogen, fats, enzymes, and organelles.

Neuromuscular Junction (NMJ)

  • Connection between motor neuron and muscle fiber;

    • Each muscle fiber innervated by a single NMJ.

    • Motor unit consists of one motor neuron and all muscle fibers it innervates.

  • Muscle fibers contract together under stimulation from the motor unit.

  • Motor units can be either fast-twitch or slow-twitch depending on the muscle fiber type stirred.

Crossbridge Cycling

  1. Resting Phase: Low calcium in myofibril.

  2. Excitation-Contraction Coupling: Calcium release triggers actin binding sites.

  3. Contraction Phase (Power Stroke): Myosin heads contract and release ADP and Pi.

  4. Relaxation Phase: Calcium pumped back, ceasing actin-myosin interactions.

Muscle Mechanics

  • Definition of Flex: Decrease angle at a joint.

  • Forces produced by muscle contractions enable movement across joints.

  • **Agonist vs. Antagonist: **

    • Agonist muscles perform the action while antagonists oppose it.

  • Additional roles include synergists and stabilizers for joint stability.

Length-Tension Relationship

  • Refers to how the tension produced during a muscle twitch is influenced by the sarcomere length before contraction.

  • Optimal length improves force production; deviations (too short/too long) can reduce effectiveness.

Muscle Fiber Types

  • Type I: Slow-twitch (oxidative), fatigue-resistant, darker due to myoglobin.

  • Type IIa: Fast-twitch (oxidative-glycolytic).

  • Type IIx: Fast-twitch (glycolytic), contract rapidly but fatigue quickly.

Fiber Type Characteristics

Characteristic

Type I

Type IIa

Type IIx

Motor Neuron Size

Small

Large

Large

Recruitment Threshold

Low

Intermediate

High

Fiber Diameter

Small

Intermediate

Large

Conduction Velocity

Slow

Fast

Fast

Fatigue Resistance

High

Intermediate

Low

Force Production

Low

Intermediate

High

Color

Red

Red/White

White

Fiber Type Distribution

  • Influences physical capacity and athletic performance. For example:

    • Soleus: High Type I composition, crucial for endurance.

    • Triceps Brachii: Higher Type II composition, transmits larger forces.

Motor Units and Principles of Activation

Principles:

  1. All-or-None: All fibers in a motor unit activate together.

  2. Size Principle: Small motor units (Type I) activated first.

  3. Gradation of Force: Achieved through frequency of activation and number of recruited units.

Force, Velocity, and Power

  • The force and velocity of contraction are inversely related.

  • Power Definition: Power is the product of force and velocity.