What type of lever system has the muscle force and resistance force working on opposite sides of the fulcrum?

In a first-class lever system, the muscle force and the resistance force act on opposite sides of a fulcrum. This type of lever is characterized by the arrangement where, for example, the fulcrum is located between the effort (muscle force) and the load (resistance force). A common example of a first-class lever in the human body is the action of the neck muscles when nodding the head. In this scenario, the fulcrum is the atlanto-occipital joint, the muscle force comes from the neck muscles pulling down on the back of the skull, and the resistance force is the weight of the head acting downward on the opposite side of the fulcrum.

The first-class lever allows for a balance of forces and can change the direction of the applied force, which makes it effective for various movements. Understanding this lever type is crucial for fitness instructors as it helps illustrate how muscles work together to produce movement efficiently.