Lever is a rigid bar which is capable of rotating about a fixed point called the fulcrum.
Example: - see-saw, scissors, pulley etc.
Skeletal system also acts like lever.
CLASS I LEVER - A first class lever has the fulcrum located between the force and the resistance.
Example- See-saw, a pair of scissors, bicycle brake. Rowing: in rowing, application of the force on the oars at the axis.
CLASS II LEVER - A second class lever has the load or resistance located between the fulcrum and the force.
Example- wheel barrow, punching machine, Straight pushups, calisthenics, lifting of legs from the ground, etc.
CLASS III LEVER - A third class lever has the force located between the fulcrum and the resistance.
Example- baseball bat, Tennis racket, boat-paddles, curling of biceps, etc.