3.2 stability and lever systems

• Stability - ability of the body to resit 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:

  mass of body - greater mass, greater stability

  height of centre of mass - lower CoM, greater stability

  base of support - greater size of BoS, greater stability

  line of gravity - more central LoG, greater stability
• Factors affecting position of centre of mass:

  • shape of body
  • distribution of mass
• factors affecting stability:

  • mass of the body
  • height of the centre of mass
  • base of support
  • line of gravity
• lever systems are the coordinators of our bones and muscles, primarily to create human movement
• functions of levers:

  • to generate muscular effort to overcome a given load
  • to increase the speed of a given movement
• components of a lever system:

  • lever (bone)
  • fulcrum (joint)
  • effort (muscular force)
  • load (weight/resistance)
• example of lever system:

  upward phase of bicep curl

  • bicep brachii is attached to the radius of the forearm
  • when bicep brachii contracts, the muscular force pulls the radius up towards the shoulder.
• 1st class lever:

  e.g extension of the neck when preparing to head a football

  
• 2nd class lever:

  e.g ball of foot in the take-off of a high jump

  
• 3rd class lever:

  e.g flexion of the elbow during a bicep curl

  
• maximising stability:

  • sprinter preparing in the blocks has maximum stability. the crouched position gives a lower centre of mass
  • the base of support is large, with 5 points of contact
  • the line of gravity falls within the base of support and sprinters typically have a high mass due to their high proportion of body mass
• minimising stability:

  • when 'set' is called sprinter lifts their hip, raising their centre of mass, raises one knee reducing points of contact, and leans forward shifting the line of gravity to the edge of the base of support.
• efficiency of a lever system:

  • the order and distance of the lever components from their fulcrum is important to their function
  • the greater the distance of the effort or load from the fulcrum the more significant the effort or load becomes
• the distance from the fulcrum to the effort is known as the effort arm
• the distance from the load to the fulcrum is known as the load arm
• mechanical advantage:

  in a 2nd class lever system where the effort arm is greater than the load arm

  effort arm>load arm

  a large load can be moved with a small effort
• mechanical disadvantage:

  in a 3rd class lever system where the load arm is greater than the effort arm

  load arm>effort arm

  a large effort can be moved with a small load