Final answer:
Most of the lever systems in the human body where muscles apply forces to bones are third-class levers, with muscles exerting significant force due to often having a mechanical advantage of less than one.
Step-by-step explanation:
In the human body, most of the lever systems formed by muscles applying forces to bones are third-class levers. These lever systems involve bones acting as stiff levers, joints functioning as fulcrums, and muscle contractions providing the effort to move a load or overcome resistance. Statics is essential for understanding the dynamics of these musculoskeletal systems, and it reveals that muscles exert far greater forces than might be expected due to the mechanical advantage often being less than one. An example of this is when the biceps muscle must exert force to hold up a book; the force changes with the flexion of the forearm due to the varying position of the joint's pivot and the changing lever arms.