Livers are divided into three categories.
- First class lever: The lever which has the falcrum between the load and the ball is called the first class lever. The 1st vertebra of the spine joins with the human crown to form the first class liver. Due to this lever, the head can be rotated forward, backward, up and down.
- Second class lever: The lever where the weight is between the falcrum and the ball is called second class lever. Class 2 levers are formed when the heel is raised by resting on the toes. Because of this lever one can run fast.
- Third class lever: The lever where the ball is between the falcrum and the load is called the third class lever. 3rd class lever is formed when an object is lifted by hand. Due to this lever, more weight can be lifted with less force.