The Biomechanics

Introduction to Kinesiology Mechanics

  • Today's lecture focuses on kinesiology mechanics, specifically integrating joint stability and muscle assessment.

  • Emphasis on biomechanics of motion.

Foundational Requirements for Effective Movement

  • Movement is not an isolated muscle action; it involves coordination among several components.

  • Three primary pillars of movement:

    • Structural Stabilization

    • Motor Coordination

    • Functional Neural Pathway

Structural Stabilization

  • Muscle contraction effectiveness relies on stabilization at one attachment point.

  • Without stabilization, muscle contraction pulls ends toward the middle, losing mechanical advantage.

  • Stabilization methods:

    • Weight Bearing (Distal Fixation):

    • Example: Performing a push-up with hands fixed against the floor.

    • Anchoring by Other Muscles:

    • Other muscles hold a bone steady while the primary muscle acts.

    • Inertia of Larger Body Parts:

    • Example: Trunk provides stability for arm movements.

Motor Coordination

  • Defined as the controlled execution of movements.

  • Elements affecting coordination:

    • Speed Control:

    • Ensures movement is safe and effective.

    • Direction Control:

    • Guides limbs along the intended path.

    • Force Control:

    • Determines muscle tension to overcome resistance without overshooting.

  • Smooth transitions between motion phases convert raw power into precise actions.

Functional Neural Pathway

  • Lower Motor Neuron:

    • Serves as the bridge between the central nervous system and muscular system.

    • Sends electrical signals needed for muscle activation.

    • Damage to this neuron halts muscle contraction, impacting joint stabilization and coordination.

Barriers to Joint Movement

  • Evaluating joint range of motion reveals distinct physical barriers impacting capacity.

Active Contraction of Antagonistic Muscles

  • Antagonistic muscle should relax to allow agonist movement; failure results in resistance.

  • Example: Muscle guarding and spasticity limit movement in clinical settings.

Passive Length of Joint Structures

  • Synovial joints encased in a fibrous capsule; ligaments provide stability, limiting elasticity.

  • If ligaments reach maximum length, movement is halted to prevent dislocation or injury.

Passive Insufficiency

  • Limitations from the physical length of muscles that cross multiple joints.

  • Example: Hamstrings crossing hip and knee; failure to stretch both leads to lack of movement.

Structural Blocks

  • Bony Limitations:

    • Occurs when bone surfaces make direct contact (e.g., olecranon process during elbow extension).

  • Soft Tissue Barriers:

    • Large muscle masses can restrict joint motion, e.g., gastroc vs. hamstring during flexion.

    • Pathological soft tissue limitations (edema) creating internal pressure restrict movement.

Roles of Muscles in Movement

  • Muscles work as a coordinated team with defined functions during any movement.

Prime Mover (Agonist)

  • The muscle or group directly generating primary force for joint motion.

  • Example: Biceps brachii during elbow flexion.

  • Role context-dependent; a muscle's function may change across movements.

Assisting Movers (Accessory Muscles)

  • Secondary muscles aiding the prime mover, showing varied activation levels based on demand.

  • Example: Diaphragm during quiet breathing vs. sternocleidomastoid during intense exertion.

Synergists

  • Definition: Muscles contributing to movement execution via contraction.

  • Example: Gastrocnemius and soleus working together for plantar flexion.

Antagonists

  • Opposing muscles providing balance and control during movement.

  • Changes roles based on the motion desires, e.g., triceps as antagonist during elbow flexion.

Principle of Reciprocal Innervation

  • When the agonist contracts, the antagonist receives an inhibitory signal to relax.

  • Prevents internal friction; critical for efficient movement.

  • Example: Driving a car requires one foot on gas, not simultaneously on the brake.

Co-contraction

  • Involves simultaneous contraction of agonist and antagonist for stability.

  • Protects joints during heavy loads or impact movements.

Movement Categorization Metrics

Strength

  • Definition: Maximum tension a muscle can exert against resistance.

  • Involves muscle fiber internal tension development, not merely external weights.

Power

  • Defined as the rate of work performed.

  • Relationship between work done and speed of completion; characterized by explosive movements.

Endurance

  • Ability of muscles to sustain activity without exhaustion.

  • Factors affecting endurance:

    • Nutritional status and local blood supply efficiency.

    • Onset of fatigue limits sustained tension.