Biomechanical Principles and Stability

Biomechanical Principles for Analysis of Human Movement

Introduction to Biomechanics

• Biomechanics involves analyzing human movement through physics and mechanics.
• Key concepts include understanding forces, levers, and their applications in sports.

Key Concepts in Biomechanics

1. Linear and Angular Concepts

• Force/Torque: Force causes motion; torque relates to rotation around an axis.
• Momentum: The quantity of motion an object has, dependent on mass and velocity.
• Impulse: Change in momentum resulting from a force applied over time.
• Speed/Velocity: The rate of change of position (speed has magnitude; velocity has direction).

2. Newton’s Laws of Motion

• First Law (Inertia): An object will remain at rest or in uniform motion unless acted upon by a force.
• Second Law (Acceleration): The acceleration of an object depends on the mass and the net force acting on it. (F = ma)
• Third Law (Action-Reaction): For every action, there is an equal and opposite reaction.

3. Projectile Motion

• Influenced by height, angle, and speed of release impacts the trajectory and distance traveled.

4. Lever Systems

Types of Levers:

• First-class levers: Fulcrum between effort and load (e.g., seesaw).
• Second-class levers: Load is between effort and fulcrum (e.g., wheelbarrow).
• Third-class levers: Effort is applied between load and fulcrum (e.g., bicep curl).

5. Mechanical Advantage (MA)

• Definition: Ratio of force arm to resistance arm.
• MA = Force Arm / Resistance Arm
• Efficiency varies:
  • 1st class levers: MA can be >, =, or < 1.
  • 2nd class levers: MA is always > 1.
  • 3rd class levers: MA is always < 1.
• Implication for athletes: Understanding lever mechanics aids in improving performance.

Stability in Sports

1. Types of Stability

• Static Stability: Ability to maintain position (e.g., standing, handstand).
• Dynamic Stability: Ability to maintain balance while in motion (e.g., catching a wave while surfing).

2. Factors Affecting Stability

• Base of Support (BOS): Greater area leads to increased stability.
• Mass: Greater mass provides more stability.
• Center of Gravity (COG): A lower COG increases stability; COG shifts with body position.
• Line of Gravity (LOG): The position of the LOG impacts stability; closer to the edge of the BOS means less stability.

3. Applications in Sports

• Certain sports (e.g., wrestling, weight lifting) require high stability.
• Other sports (e.g., sprinting, tennis) require lower stability for quick movements.
• Techniques: Athletes may manipulate their BOS, COG, and LOG to improve performance and balance as needed.

4. Practical Implications

• Techniques such as keeping COG low through bending knees can enhance stability.
• Some sports may need athletes to reduce stability to increase agility and response time.