Levers
Levers in our body are formed from bones, joints and muscles.
A lever consists of:
- a rigid structure (bone)
- a force acting upon it (muscle) to produce a turning movement (angular motion)
- a fulcrum which is a fixed point (joint)
- a load or resistance that is placed on the rigid structure (weight of body part being moved and anything that it is carrying)
There are three types of lever.
1. First class lever 鈥 the fulcrum is in the middle of the effort and the load.
This type of lever is found in the neck when raising your head to head a football. The neck muscles provide the effort, the neck is the fulcrum, and the weight of the head is the load.
2. Second class lever 鈥 the load is in the middle between the fulcrum and the effort.
This type of lever is found in the ankle area. When standing on tiptoe, the ball of the foot acts as the fulcrum, the weight of the body acts as the load and the effort comes from the contraction of the gastrocnemius muscle. This second class lever is used when taking off for a jump or pushing against the blocks in a sprint start.
3. Third class lever 鈥 the effort is in the middle between the fulcrum and the load.
During a biceps curl, the fulcrum is the elbow joint, the effort comes from the biceps contracting and the resistance is the weight of the forearm and any weight that it may be holding.
Mechanical advantages of levers
When a lever's effort arm is longer than its load arm, it is said to have high mechanical advantage. Levers with high mechanical advantage can move large loads with a relatively small amount of effort. Second class levers always have high mechanical advantage. First class levers can have high mechanical advantage, if the fulcrum is close to the load.
To recall the order of the levers use the term 'FLE' - this will help you to remember which part of the lever is in the middle.
First class lever - Fulcrum is in the middle.
Second class lever - Load is in the middle.
Third class lever - Effort is in the middle.