Balance and Stability in Biomechanics

Key Concepts

• Center of Mass (CoM)

  • Imaginary point where mass is evenly distributed in all directions.
  • Also referred to as Center of Gravity (CoG).
  • Not a fixed point; it moves with the body's position.
  • Examples:
    • Arms raised: CoM moves upward.
    • Bending forward: CoM can move outside the body.

• Base of Support (BoS)

  • The area of contact between the body and the ground.
  • Wider BoS increases stability.
  • Narrow BoS decreases stability.

Importance in Sports

• Essential for activities involving direction changes, tackling, etc.
• Poor balance increases risk of injuries (e.g., falling, sprains).
• Lowering CoM improves balance.
• Line of Gravity:
  • For optimal balance, CoM should be directly above BoS.

Factors Affecting Balance and Stability

• Height of CoM: Lower CoM leads to greater stability.
• Width of BoS: Wider BoS leads to increased stability.
• Line of Gravity: Better balance when it falls within BoS.
• Body Mass: Greater body mass leads to greater stability due to increased inertia (Newton’s First Law).

Practical Applications

• Rugby Example: Wide stance and low CoM for stronger tackles and higher stability.
• High Jump Techniques:
  • Traditional methods (pre-1970s) vs. Fosbury Flop.
  • Fosbury Flop allows CoM to pass under the bar, enabling higher jumps for less effort.

Situations for Reduced Balance and Stability

• Agility in Sports:
  • Narrow BoS and high CoM for quick side steps or swerves.
  • Example: Jonny Wilkinson’s kicking position.
• Accelerating in Sprinting:
  • Lean forward to push CoM ahead and initiate rapid acceleration.
  • Example: Dina Asher-Smith’s sprinting technique.

Conclusion

• Understanding CoM and BoS helps in maximizing performance and safety in sports.
• Adjusting these factors can boost balance for static activities or reduce balance for dynamic movements.