Study Notes for DPT 6101 Clinical Biomechanics

DPT 6101 Clinical Biomechanics

Introduction

• Presented by Chris Wendt, MS Lab Manager/Instructor and Judy Foxworth.

• Exclusive material for students enrolled in DPT 6101 at Winston-Salem State University.

• Copyright © 2026, prohibits duplication without permission.

Course Objectives

• Understand the differences between Biomechanics and Kinesiology.

• Learn fundamental movement patterns.

• Review planes and axes of motion.

• Discuss Newton’s Laws of Motion.

• Explore lever systems in the body.

• Define the center of mass.

What is Biomechanics?

• Definition:
    - A branch of Kinesiology that investigates the physical nature of biological systems.
    - The study of the structure and function of biological systems using mechanics.
    - Dynamics of forces acting on and generated within the body, and their effects on tissues, fluid, or materials for diagnosis, treatment, or research.
    - Application of mechanical principles to human movement.

• Visual Concept: Biomechanics is the intersection of Biology and Physics.

Terminology in Biomechanics

• Kinematics: Analysis of human movement in terms of position, velocity, and acceleration.

• Kinetics: Examination of the forces causing movement, including ground reaction force, torque, and power.

• Functional Anatomy: Relation to how human anatomy performs within these mechanical concepts.

• Types of Movement:
    - Linear Movement: Displacement in a straight or curved path.
    - Angular Movement: Rotational motion around an axis.

Fundamental Movement Patterns

1. Linear Movement
      - Translational Motion: Movement from one point to another.
      - Two Types:
        - Rectilinear Translation: Straight-line movement.
        - Curvilinear Translation: Movement along a curved path.
      - Examples:
        - Jumpers demonstrating verticality.
        - Runners or skaters negotiating a curve.

2. Angular Movement
      - Displacement occurs around an axis, involving joint movements (hip, knee, ankle).
      - Requires coordination of joint rotations for effective mobility.

Planes of Movement

1. Sagittal Plane (medial-lateral axis)
      - Involves movements like flexion and extension.

2. Frontal Plane (anterior-posterior axis)
      - Involves movements like abduction and adduction.

3. Transverse Plane (longitudinal axis)
      - Divides the body into superior and inferior portions.

Newton's Laws of Motion

Overview of Laws

• Mass and motion relate to forces in predictable ways.

• Three laws define how and when a force creates movement:
    1. Newton’s 1st Law - Law of Inertia
    2. Newton’s 2nd Law - Law of Acceleration
    3. Newton’s 3rd Law - Law of Action-Reaction

Law of Inertia – Newton’s 1st Law

• Definition: Every object remains in its state of rest or uniform motion in a straight line unless acted on by external forces.

• Inertia: Resistance to a change in motion is proportional to mass.

• Observational Example: When pressing the UP button in an elevator with legs bent, one experiences upward force.

Angular Motion of Inertia

• Remains stationary or rotates with constant velocity unless an external torque acts on it.

• Rotational Inertia: Resistance, or moment, defined mathematically as:
    $I = m imes r^2$
    - Resistance is influenced by the mass of the object and its radius/length.
    - Example: A tightrope walker’s pole stabilizes against rotation due to its mass and length.

Law of Acceleration – Newton’s 2nd Law

• Definition: A force accelerates an object in the direction of the force, at a rate inversely proportional to its mass.

• Mathematical Formulation:
    $F = m imes a$

• Key Principles:
    - Force is an external push/pull affecting momentum, which can be described with:
      - $p = m imes v$
    - Changes in momentum result from applied force over time.

Law of Action-Reaction – Newton’s 3rd Law

• Definition: For every action, there is an equal and opposite reaction.

• Angular Reaction: When one object exerts torque on another, an equal and opposite torque is applied back.

• Applications include understanding ground reaction forces and contact forces during movement.

Skeletal Movement and Lever Systems

• Definition of a lever: A rigid object rotating around an axis.

• Leverage: The ability to create torque around a fixed point, affected by distance from the fulcrum.

Types of Lever Systems

1. First Class Lever: Fulcrum between resistance and motive forces (e.g., neck muscles supporting the head).

2. Second Class Lever: Resistance closer to the fulcrum than the motive force (e.g., calf muscles lifting the body).

3. Third Class Lever: Motive force closer to the fulcrum than resistance (e.g., bicep curl).

Lever Components

• Effort Arm (EA): Internal moment arm.

• Resistance Arm (RA): External moment arm.

• Formula for Mechanical Advantage:
    $ext{MA} = rac{EA}{RA}$

Center of Mass (COM)

• Definition: Point around which mass is distributed, often called the balance point of the body.

• Characteristics:
    - Can refer to the entire body or individual segments.
    - Dynamic and influenced by body posture.
    - Important for determining how the body reacts to external forces.

Application of Center of Mass

• COM affects body stability in upright postures.

• Changes in body position, such as leaning forward, increase demand on spinal muscles.

Summary of Key Concepts

• Kinesiology is a qualitative study of human movement; biomechanics includes both qualitative and quantitative perspectives.

• Body motion occurs in defined planes and around axes.

• Newton's Laws provide a framework for understanding dynamics and forces.

• Most movements in the body leverage third-class lever systems, and the COM is a central consideration in movement efficacy.

Assignments

• Complete Homework 1 from Week 1 Module by April 2nd at 10:00 am.

• Submission options: electronically or printed and legibly written, uploaded in Canvas.