In-Depth Notes on Movement Analysis

I. Neuromuscular Function

• The Motor Unit:
  • Composed of a motor neuron and the muscle fibers it innervates.
  • Integral for muscle contraction and movement.
• Neuromuscular Junction Structure:
  • Components:
  • Axon Terminals: release neurotransmitters.
  • Synaptic Vesicles: store acetylcholine (ACh).
  • Synaptic Cleft: space between axon terminal and muscle fiber.
  • Postsynaptic Membrane: contains receptors for ACh.
  • Process: Nerve impulse initiates the release of ACh, leading to muscle contraction.

II. Structure of Muscle Tissue

• Components:
  • Tendons: connect muscle to bone.
  • Epimysium: outer layer surrounding whole muscle.
  • Perimysium: surrounds fascicles (bundles of fibers).
  • Endomysium: surrounds individual muscle fibers (cells).
  • Muscle Fiber: the basic unit, composed of myofibrils and myofilaments (actin and myosin).

III. Role of Neurotransmitters in Contraction

• Acetylcholine (ACh): Increases muscle membrane permeability to ions, facilitating impulse spread.
• Cholinesterase: Enzyme that breaks down ACh to re-polarize muscle fibers after contraction; prevents continuous stimulation.

IV. Skeletal Muscle Contraction

• Contraction Mechanism:
  • Sliding Filament Theory:
  1. Ca2+ release from sarcoplasmic reticulum.
  2. Binding of Ca2+ to troponin allows myosin heads to attach to actin (cross-bridge formation).
  3. Myosin heads pull actin filaments (power stroke).
  4. Myosin heads detach when new ATP binds.
  5. Structural changes: A band stays the same, while I band and H zone diminish.

V. Types of Muscle Fibers

• Slow Twitch (Type I):
  • Smaller diameter, red color, high in mitochondria/myoglobin, fatigue-resistant, primarily aerobic metabolism.
• Fast Twitch:
  • Type IIA: Larger diameter, white, moderate mitochondria, uses both aerobic and anaerobic energy.
  • Type IIB: Similar to Type IIA but mainly glycolytic (anaerobic).

VI. Joint Actions and Muscle Contraction Types

• Joint Actions:
  • Abduction: Movement away from body.
  • Adduction: Movement toward body.
  • Flexion: Decreases joint angle.
  • Extension: Increases joint angle.
• Muscle Contraction Types:
  • Isotonic (concentric & eccentric): Muscle changes length.
  • Isometric: Muscle tension without length change.
• Reciprocal Inhibition: Antagonistic muscles work in opposition; agonist contracts while antagonist relaxes.

VII. Biomechanics Concepts

• Force: Defined as mass times acceleration (F = ma); measured in Newtons.
• Speed: Rate of motion; distance over time.
• Distance vs. Displacement:
  • Distance: total path traveled.
  • Displacement: shortest path between two points.
• Velocity: displacement over time; includes direction (vector quantity).
• Acceleration: rate of change of velocity; can be positive or negative.
• Momentum: mass times velocity; can be increased by increasing either mass or velocity.
• Impulse: Product of force and the time interval it acts over; also a vector quantity.

VIII. Levers in the Human Body

• First Class Lever: Fulcrum between effort and load (e.g., triceps extension).
• Second Class Lever: Load between fulcrum and effort (e.g., heel raise).
• Third Class Lever: Effort between load and fulcrum (e.g., bicep curl).

IX. Newton’s Laws of Motion

• First Law: Objects remain at rest or in uniform motion unless acted upon.
• Second Law: F = ma; force relates to mass and acceleration.
• Third Law: For every action, there is an equal and opposite reaction.

X. Projectile Motion & Factors

• Projected Object: An object following a parabolic path under gravity.
• Factors:
  • Release Velocity: Higher velocity = greater distance.
  • Angle of Release: Optimal angles (35°-45°) yield maximum distance.
  • Height of Release: Higher release height results in greater distance.

XI. The Bernoulli Principle

• Fluid Dynamics: Increase in fluid velocity results in decreased pressure.
• Application in Sports: Explains flight dynamics of projectiles such as golf balls.