Every lever has a load arm and an effort arm. The load arm (the length from the fulcrum to the load) is the arm that carries the load and the effort arm (the lenth of the fulcrum to where the effort is) is the arm the the effort is applied to. The position of the fulcrum will affect the length of the load arm and effort arm. If you change the length of these, you can change the amount of effort you need to apply to the lever.
Links
Intro
Load Arm and Effort Arm
Levers and Friction
Classes Of Levers
Human Levers
Wheels
Bibliography