Biomechanics and Kinesiology Concept Notes

Learning Outcomes

  • 4.1 Newton’s Laws of Motion: Explain inertia, acceleration, and action-reaction in human motion.
  • 4.2 Static vs Dynamic Equilibrium: Compare and contrast both states.
  • 4.3 Concept of Acceleration: Discuss its implications.
  • 4.4 Moment of Inertia: Define and understand its significance.
  • 4.5 Mass and Force Influence on Acceleration: Explain how these elements affect object movement.
  • 4.6 Ground Reaction Forces: Discuss the action-reaction concept.
  • 4.7 Work and Energy: Relationship using potential and kinetic energy principles.
  • 4.8 Power in Human Movement: Relate power concepts to movement.
  • 4.9 Lever Systems: Define first, second, and third-class levers with examples from the human body.
  • 4.10 Mechanical Advantage: Demonstrate its concepts in biomechanics.
  • 4.11 Anatomical Pulleys: Identify and explain their roles in the musculoskeletal system for mechanical advantage.

Newton’s Second Law of Motion - The Law of Acceleration

  • Definition: Acceleration is the rate of change of velocity over time.
  • Proportionality: Acceleration is directly proportional to the force applied.
  • Directionality:
    • Linear acceleration: same direction as the applied force.
    • Angular acceleration: related to torque.

Application of Newton’s Second Law in Motion

  • Forces in Static Equilibrium:
    • Formula: F = M imes A
    • Forces act equally and oppositely with no net acceleration.
  • Torque in Angular Motion:
    • Torque = Force × Moment Arm.
    • Equal torque results in no movement.
  • Moment of Inertia Formula: I = mr^2 (mass times the square of the distance from the axis)

Types of Muscle Contraction

  • Concentric vs Eccentric:
    • Isometric: Torques are equal, muscles contract without movement.
    • Isotonic: Movement occurs, characterized by:
      • Concentric: Muscle shortens.
      • Eccentric: Muscle lengthens.
  • Force Couples: Two or more forces acting in opposite directions produce rotary motion (e.g., pelvic tilt).

Ground Reaction Forces (GRF)

  • Newton’s Third Law of Motion: For every action, there’s an equal and opposite reaction.
  • Implication: Understanding GRF is critical in biomechanics, especially during movement analysis like gait.

Work-Energy Relationships

  • Linear Work: W = F imes D (Work equals force times distance).
  • Angular Work: W = ext{Torque} imes ext{Angular Displacement}
  • Potential Energy: Energy stored based on position (e.g., height).
    • Example: Stretched rubber band.
  • Kinetic Energy: Energy of a moving object.
  • Power: Amount of work done per unit of time, given by P = W/T.

Lever Systems in the Human Body

  • First-Class Levers: Axis located between effort and resistance, designed for balance.
    • Example: Neck muscles support the head.
  • Second-Class Levers: Effort arm > Resistance arm. Resistance between fulcrum and effort.
    • Example: Calf muscles during standing on tiptoes.
  • Third-Class Levers: Most common type, internal force closer to joint axis.
    • Example: Bicep curl.

Mechanical Advantage (MA)

  • Definition: Efficiency of lever systems; longer effort arms yield higher MA.
  • MA Formula: MA = rac{ ext{Length of effort arm}}{ ext{Length of resistance arm}}
    • IMA > 1 indicates increased MA; IMA < 1 indicates decreased MA.
  • Effect of Lever Types on MA:
    • Second-class levers: more MA, less movement.
    • Third-class levers: less MA, more displacement (greater range of motion).

Anatomical Pulleys

  • Function: Increase mechanical advantage in muscle action.
  • Examples: Rotator cuff muscles acting around joint axes enhance force effectiveness.

Gait Analysis and Disorders

  • Common Gait Disorders:
    • Antalgic gait
    • Ataxic gait
    • Trendelenburg gait
    • Parkinsonian gait (Shuffling)
    • Steppage gait

References

  • Samuels, V. (2018). Foundation in Kinesiology and Biomechanics. F.A. Davis Company, Philadelphia, PA.