Physics

[jdjohnson50]

one pulls and one pushes.

There is no muscle in the human body that "pushes". Combine that piece of knowledge with all the others that are wrong in your post.

[Joe Brock]

FYI: Before you respond with something that will force me to question what is wrong with the world....
....a wrench is a lever.

[Jamie J. Skibicki]

http://www.professorbeaker.com/lever_fact.html

that took me 10 seconds (yes I timed it) to find with google. Next time, pay attention in your physics classes and do some research.

[JMT]

The OP is using too narrow a definition of lever. There are, in fact, three classes of levers, each with different relative locations of the fulcrum, the load and the force.

Class 1 Lever: The fulcrum is located between the force and the load. (crowbar, seesaw, etc.)
Class 2 Lever: The load is situated between the fulcrum and the force (wheelbarrow, nutcracker, etc.)
Class 3 Lever: The force is applied between the fulcrum and the load (tweezers, the human mandible, etc.)

The typical system of bone/joint/muscle/load found in the human body is a class 3 lever. If you did not learn this in high school physics you either had a shitty teacher or were not paying attention.

[imnotbncre8ive]

For example, when you attempt to curl a dumbbell.
The tension of the biceps muscles attached to the forearm bones (forgive my anatomy ignorance) as the "effort", the weight of the dumbbell you are attempting to curl as the "load", pivoting about the elbow joint, constitutes a class 3 lever system as illustrated, yes?

...
A force applied by pushing down on one end of the lever results in a force pushing up at the other end.
...

The definition you gave from the Science Dictionary seems to only describe a class 1 lever system. The 'effort' and 'load' don't necessarily have to be on different sides of the fulcrum to be called a lever system.

[oenamen]

The skeletal system is a system of levers.
When doing a curl, your biceps apply force between the joint (the fulcrum) and the load in your hand. The joint is being used as a class III lever.
In a triceps extension, the joint is between the load and the force applied by your triceps. The same joint is now being used as a class I lever.

A pulley is not a lever.

[elVarouza]

What about this?
"A force applied by pushing down on one end of the lever results in a force pushing up at the other end."
That definitely does not happen in the system you described.
Joints and their components seem to be more like pulleys (which someone told me is a type of lever), but I do not think even that label is accurate.

If you're really interested in stuff like this, I recommend taking a course in physics. This is one of Newton's Laws: every action has an opposite and equal reaction. In the case of, say, a squat, as the weight on your back pushes you down, your muscles/joints push up on the bar. If this was not the case, your body would collapse under the weight.

[BrewinBombers]

Dude, you're focusing on the example and not the definition. By your strict trollpretation, a lever cannot have force applied up on one end and pushed down on the other.

[Roy]

i think you need to skip ahead and take a philosophy of language course.

[mikednj]

http://www.innerbody.com/image_musc04/musc73.html

I don't think it gets much simpler or more clear than that.