Levers and Mechanical Advantage

• Components of a Lever

  Fulcrum (joint), Load (weight/resistance), Effort (Muscle).
• First class lever


  Fulcrum in the middle.
• Second class lever


  Load in the middle.
• Third class lever


  Effort in the middle.
• First class lever movement

  Elbow extension

  Fulcrum - Elbow joint.

  Load - Weight of the lower arm and the ball.

  Effort - Triceps contract.
• Second class lever movement

  Plantar flexion

  Fulcrum - Ball of the foot.

  Load - Weight of the person.

  Effort - Gastrocnemious contracts.

  Dorsiflexion

  Fulcrum - Heel of the foot.

  Load - Weight of the person.

  Effort - Contraction of the tibialis anterior muscle.
• Third class lever movement

  Elbow flexion

  Fulcrum - Elbow joint.

  Load - Weight of the lower arm plus weight.

  Effort - Force applied by the biceps as it pulls the lower arm upwards.

  Flexion and extension at the knee

  Fulcrum - Knee joint.

  Load - Weight of lower leg and foot.

  Effort - Force applied by hamstring muscle as it contracts to pull the lower leg upwards.
• Mechanical advantage


  The benefit to a lever system of having either a short load/resistance arm giving the advantage of being able to move a heavy weight or short effort arm - giving rapid movements over a large range of movement.
• Mechanical advantage=effort arm/load (resistance) arm.
• The majority of joints are third class lever system, with a short effort arm and long resistance arm. This means that these joints have low mechanical advantage.
• Short effort arm


  Rapid movements over a large range of movements.
• Short load/resistance arm


  Advantage of being able to move heavy weight and apply a large force.
• 2nd class levers


  Are able to overcome a large resistance with an effort that is fairly small in comparison because the effort arm is longer than the load arm.