What defines a first-class lever in biomechanics?

A first-class lever is defined by having the axis of rotation positioned between the force applied and the resistance the lever must overcome. This arrangement allows for the force and resistance to be on opposite sides of the axis, which can facilitate efficient movement and leverage.

In practical terms, a classic example of a first-class lever is a seesaw or a pair of scissors, where the pivot or fulcrum is in the middle. When force is applied on one side (either by pushing down or pulling up), it causes the opposite side to move in response, effectively lifting or moving the resistance. This configuration allows for a considerable mechanical advantage, depending on the distances from the axis to the force and the resistance.

The concept illustrates the importance of lever mechanics in physical performance and rehabilitation, where understanding the lever systems can help in designing effective training or therapy regimens.