Biomechanical Principles: stability and lever systems

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  • Biomechanical Principles: stability and lever systems
    • Centre of Mass
      • The point at which a body is balanced in all direction in all directions; the point from which weight appears to act.
      • If an athlete stands in the anatomical position, it will be around their naval.
        • It’s location is dependent on the distribution of body mass and can be manipulated to improve sporting technique by altering body shape.
      • If an athlete raises their arms, the centre of mass will also rise.
        • If they bend their knees their centre off mass will also lower.
      • The centre of mass can also move outside the body and act as a point of rotation.
        • For example, a gymnast performing a front tucked somersault moves their centre of mass in front of the body and rotates around it
    • Stability
      • The ability of a body to resist motion and remain at rest, or for a body to withstand a force applied and return to its original position without damage.
      • Factors affecting stability:
        • Height of the centre of mass.
          • The lower the centre of mass the greater the stability.
        • Base of support.
          • The greater the size of the base of support the greater the stability.
        • Mass of the body.
          • The greater the mass of a body the greater it’s inertia, and therefore, the greater it’s stability.
        • Line of gravity.
          • The more central the line of gravity to the base of support the greater the stability.
    • Lever Systems
      • Lever systems have two main functions:
        • To generate muscular effort to overcome a given load.
        • To increase the speed of a given moment.
      • lever= bone, fulcrum= joint, effort= muscle force, load= weight/resistance
      • 1st Class Lever
        • Fulcrum is in the middle E-F-L (English Football League)
          • Extension of the neck when preparing to head a football
      • 3rd Class Lever
        • Effort is in the middle F-E-L (fell)
          • Flexion of the elbow during a bicep curl
        • most levers in the body are third class levers
      • 2nd Class Lever
        • Load is in the middle E-L-F (elf)
          • Ball of the foot in the take-off phase of a high-jump
      • Mechanical Advantage:
        • second-class lever systems where the effort arm is greater than the load arm. A large load can be moved with a relatively small effort.
      • Mechanical Disadvantage:
        • Third-class lever systems where the load arm is greater than the effort arm. A large effort is required to move a relatively small load.


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