Final answer:
Muscles provide the effort in the human body's lever system, pulling on bones to facilitate movement, with bones acting as levers and joints as fulcrums.
Step-by-step explanation:
In the lever system of the human body, the muscles provide the effort needed for movement. When we look at the musculoskeletal system, we see that bones act as levers and joints function as the fulcrums. Muscles are connected to bones by tough connective tissues known as tendons, and when these muscles contract, they pull on the bones, causing them to move. This contraction represents the effort that moves the levers (bones) around the fulcrums (joints), enabling our body to perform various actions.