Biology of Biomechanics and Kinesiology WEEK 1

1. Understanding Force and Vectors

1.1 Characteristics of Force

• Definition: An interaction that, when unopposed, will change the motion of an object.

• Key Descriptors:

  • Magnitude: How strong the force is ($10 \text{ N}$ vs. $5 \text{ N}$).

  • Direction: Which way it's pushing or pulling.

  • Point of Application: Where on the object the force is applied.

  • Line of Action: The imaginary line along which the force acts.

• Units: Newtons ($\text{N}$).

1.2 What is a Vector?

• Definition: A quantity that has both magnitude (size) and direction.

• Importance: Forces are vectors.

1.3 Visualizing Vectors

• Represented with arrows.

  • Length: Shows magnitude.

  • Direction the arrow points: Shows the direction.

1.4 Body Forces

• Gravity: Pulls objects down.

• Muscle Force: Generated by muscle contractions.

• Joint Reaction Force: Forces between bone surfaces in a joint.

• Friction: Opposes motion between surfaces.

1.5 Concurrent Forces

• Definition: Two or more forces acting on an object at the same point of application or whose lines of action intersect.

• Result: Combine to create a resultant force.

2. Force in Kinesiology: Muscles

2.1 Focus in Kinesiology

• Understand how forces create movement or stability in the human body.

• Helps analyze injuries, athletic performance, and rehabilitation exercises.

2.2 How Muscles Create Force

• Muscles generate force by contracting (shortening).

• Contraction pulls on tendons, attached to bones.

• Generates tension, leading to movement.

2.3 Key Factors in Muscle Force

1. Length-Tension Relationship: Muscles produce most force at an optimal length.

2. Force-Velocity Relationship: Less force when contracting quickly, more force when contracting slowly.

3. Physiological Cross-Sectional Area (PCSA): Bigger muscles (more muscle fibers) produce more force.

2.4 Importance of Muscle Anatomy

• Origin: Stable attachment point.

• Insertion: Movable attachment point.

• Fiber Type:

  • Type I (Slow-twitch): Endurance.

  • Type II (Fast-twitch): Power.

3. Levers: The Body's Mechanics

3.1 Connecting to Levers

• Muscles apply force to bones (levers) to move loads.

3.2 Definition of a Lever

• Definition: A rigid bar (bone) that pivots around a fixed point (joint/fulcrum) to transmit force.

• Key Components:

  • Fulcrum (F): Pivot point (joint).

  • Effort (E): Force applied (muscle contraction).

  • Resistance (R): Load to be moved (body part, external weight).

3.3 Synonyms

• Fulcrum: Axis, Pivot Point.

• Effort: Force, Muscle Force, Applied Force.

• Resistance: Load, Weight, Opposing Force, Gravity.

3.4 Key to Memorization

• Remember FRE (for the order of components) or 1-2-3 (for the classes).

3.5 Historical Insight

• Principles described by Archimedes (around $260$ BC).

3.6 Description of Arrangement (Lever Classes)

1. First-Class Lever (FRE): Fulcrum is between the Effort and Resistance.

2. Second-Class Lever (F*R*E): Resistance is between the Fulcrum and Effort.

3. Third-Class Lever (FR*E*): Effort is between the Fulcrum and Resistance.

3.7 Examples of Lever Classes

• First-Class Lever:

  • Body Example: Head balancing on neck.

  • Everyday Example: See-saw.

• Second-Class Lever:

  • Body Example: Standing on tiptoes.

  • Everyday Example: Wheelbarrow.

• Third-Class Lever:

  • Body Example: Bicep curl.

  • Everyday Example: Fishing rod.

3.8 Lifting Techniques

• Keep the object close to your body (reduces resistance arm).

• Use your legs, not your back.

4. Applying Force: Torque and Biomechanics

4.1 Example of Torque Calculation

• Definition: The rotational effect of a force around an axis.

• Formula: Torque ($\tau$) = Force ($F$) $\times$ Perpendicular Distance from Fulcrum ($d$)

  • $\tau = F \times d$

• Example: $50 \text{ N}$ force on $0.2 \text{ m}$ wrench = $10 \text{ Nm}$ torque.

4.2 Modeling the Elbow and Forearm

• Elbow = fulcrum.

• Biceps muscle = effort force.

• Dumbbell = resistance force.

• Understanding torque explains why a dumbbell feels heavier the further it is from your elbow.

5. Movement Patterns: Open vs. Closed Chain

5.1 Definition (Open Chain Movement)

• The distal segment (e.g., hand, foot) is free to move and not fixed against a surface.

5.2 Characteristics (Open Chain Movement)

• Non-weight-bearing movements.

• Movement primarily at one joint (isolated).

• Used for isolated muscle strengthening or range of motion.

5.3 Relevance (Open Chain Movement)

• Examples: Bicep curls, leg extensions, kicking a ball.

• Good for early rehab.

5.4 Definition (Closed Chain Movement)

• The distal segment is fixed against an immovable surface.

5.5 Illustrative Examples (Closed Chain Movement)

• Examples: Squats, push-ups, lunges.

• The body moves relative to the fixed distal segment.

5.6 Importance in Occupational Performance (Closed Chain Movement)

• Functional: Mimics daily activities (e.g., walking, climbing stairs).

• Involves multiple joints and muscles (co-contraction).

• Associated with weight-bearing and stability.

• Crucial for balance and proprioception.