Foundations of Occupation: Kinesiology and Biomechanics

Foundations of Occupation: Kinesiology and Biomechanics

Introduction to Kinesiology and Biomechanics

  • Understanding the foundations of occupation is crucial, especially concerning kinesiology and biomechanics. This lecture covers fundamental concepts in biomechanics including:

    • Kinetics

    • Forces

    • Point of Application and Line of Pull

    • Torque

    • Biomechanical Levers

    • Kinematics

Kinematics

Definition of Kinematics

  • Kinematics: The study of motion without considering the forces that cause it.

Types of Motion

  • Translation (Linear Motion): All parts of the object move at the same time, in the same direction, and at the same distance.

    • Rectilinear Motion: Example: A person sliding down on a sled.

    • Curvilinear Motion: Example: A thrown ball or javelin.

  • Rotation (Angular Motion): All parts of the object move at the same time in the same direction but at different distances

    • Examples include flexing the knee or elbow.

Human Movement Mechanics

  • Combination of Motion: Human movement often involves both translatory and rotatory motion, where “the entire object is moving in a linear fashion & the individual parts are moving in an angular fashion” (Lippert, 2011, p. 6).

Arthrokinematic Motion

Types of Arthrokinematic Motions

  • Roll: Multiple points on one rotating articular surface contact multiple points on another articulating surface.

    • Example: Ball and socket joints such as the hip (femoro-acetabular) and shoulder (glenohumeral).

  • Slide (Glide): A single point on one articular surface contacts multiple points on another articular surface.

    • Example: Plane joints where surfaces are irregularly shaped, such as intercarpal bones of the hand.

  • Spin: A single point on one articular surface rotates on a single point on another articular surface.

    • Example: Pivot joints like the humeral-radial joint allowing forearm supination/pronation.

Joints Mechanics

Concave and Convex Surfaces

  • Most joints engage in roll, slide, and sometimes spin simultaneously.

Rolling and Sliding Mechanics

  • Convex-on-Concave Rule: When a convex joint surface moves on a concave surface, roll and slide occur in opposite directions.

  • Concave-on-Convex Rule: When a concave surface moves on a stationary convex surface, roll and slide occur in the same direction.

Examples of Motion

  • Glenohumeral Joint: The mechanics of roll and slide movement within this joint are critical for understanding shoulder function.

  • Knee Joint: Involves complex roll and slide mechanisms that must be comprehended for movement analysis.

Open-Chain and Closed-Chain Motion

  • Open-Chain Motion: In this type of movement, the distal segment moves around a more stationary proximal segment. Example: Leg extensions.

  • Closed-Chain Motion: Proximal segment moves around a stationary distal segment. Example: Squats, where the feet remain planted.

Kinetics

Definition of Kinetics

  • The study of forces acting on the body and how they influence motion.

Types of Forces

  • Forces can:

    • Initiate motion

    • Stop motion

    • Prevent motion

Types of Forces Acting on the Body

  • Internal Forces: Forces produced by muscles within the body.

  • External Forces: Forces applied from outside the body, such as gravity.

Components of Force

  • Force: Defined as the product of mass and acceleration.

    • Equation: F=mimesaF = m imes a (where F is force, m is mass, and a is acceleration).

  • The effectiveness and direction of forces are crucial in analyzing human movement and biomechanics.

Forces and Movement

Center of Gravity (COG)

  • COG in Objects: The point where mass is evenly distributed in all directions.

  • Human Body: Generally located a little anterior to the S2 vertebra; however, its precise location varies based on body positioning and motions.

Force Systems in Motion

  1. Linear Force Systems: Forces act in the same direction along the same line.

  2. Parallel Force Systems: Forces act on the same object in parallel.

  3. Concurrent Force Systems: Multiple forces acting at a common point in divergent directions.

  4. Force Couple: Two or more forces acting in different directions to create a turning effect.

Biomechanical Levers

Components of Levers

  • A lever consists of the following four components:

    • A Rigid Bar: The bone in the body.

    • An Axis: The joint or pivot point.

    • An Effort Force: The muscles applying the force.

    • A Resistance Force: Acting against the motion (gravity or weight).

Classification of Levers

  1. First-Class Lever: Resistance force and effort force are on either side of the axis. Example: Neck extension.

  2. Second-Class Lever: Resistance force is between the effort force and axis. Example: Standing on tiptoes.

  3. Third-Class Lever: Effort force is between the resistance force and axis. Example: Bicep curl.

Mechanical Advantage

  • The ratio of the effort arm to the resistance arm.

    • Equation for Mechanical Advantage: MA=racEARAMA = rac{EA}{RA} (where EA is the effort arm and RA is the resistance arm).

    • Interpretation of MA:

    • $MA > 1$ indicates a good mechanical advantage.

    • $MA < 1$ indicates a poor mechanical advantage.

Torque

  • Torque Definition: The rotary equivalent of a force. It involves a force causing rotation around an axis.

    • Components:

    1. Force

    2. Moment Arm: The perpendicular distance from the line of force to the axis of rotation.

  • Torque Calculation:
    extTorque=extForceimesextMomentArmext{Torque} = ext{Force} imes ext{Moment Arm}

Internal and External Torque

  • Internal Torque: Produced by internal forces (like muscles) and their moment arms.

  • External Torque: Produced by external forces (like gravity) and their moment arms.

Efficiency in Torque Management

  • Adequate internal torque is crucial to counteract external torque, enhancing movement efficiency.

Conclusion

  • The complex interplay between kinematics, kinetics, and biomechanical principles informs understanding and application in fields such as occupational therapy and physical rehabilitation. Understanding these dynamics is essential for optimizing human movement and addressing dysfunctions effectively.