Lever systems

• Lever Systems


  When the muscular and skeletal systems work together, they create lever systems that help us to move
• Lever

  • A rigid bar that moves about a fixed point when force is applied to it
• Lever Systems Help the Body to Move

  1. Muscle pulls on a bone to move a body part about a joint

  2. Uses the body part as a lever

  3. Lever makes up part of a lever system
• Components of a lever system

  • Lever arm (the bone or body part being moved about a point)
  • Fulcrum (the joint where the lever arm pivots)
  • Effort (the force applied by the muscles to the lever arm)
  • Load or resistance (the weight of the body, body part, or something being lifted)
• Lever arm


  • Shown as a straight line on a diagram
• Fulcrum


  • Shown as a triangle on a diagram
• Effort


  • Shown by an arrow pointing in the direction of the force
• Load or resistance


  • Shown as a square or an arrow
• Types of lever systems

  • 1st Class (load and effort at opposite ends, fulcrum in the middle)
  • 2nd Class (fulcrum and effort at opposite ends, load in the middle)
  • 3rd Class (fulcrum and load at opposite ends, effort in the middle)
• 1st Class lever


  • Neck extension (e.g. heading a football
• 2nd Class lever


  • Standing on your toes (e.g. before you jump)
• 3rd Class lever


  • Elbow flexion (e.g. lifting a weight)
  • Flexion and extension at the shoulder, hip and knee
• Mechanical Advantage

  • If a lever provides mechanical advantage, it can move a larger load with a smaller effort
  • For a lever providing mechanical advantage, the effort arm (the distance between the fulcrum and the effort) is longer than the weight (resistance) arm (the distance between the fulcrum and the load)
  • Mechanical advantage = effort arm / weight (resistance) arm
• Second class levers always provide mechanical advantage - the effort arm is always longer than the weight arm
• First class levers can provide mechanical advantage - it depends whether the fulcrum is nearer to the effort or to the load
• Third class levers never provide mechanical advantage
• 123


  FLE
• NAE

  (NECK, ANKLE, ELBOW)