Class 1 levers are where the fulcrum is between the load arm and the effort arm. This can make the mechanical advantage more than 1, less than 1 or 1. An example is a pry bar opening a can. The fulcrum is in the middle of the pry bar where the bend is. Also an example would be a teeter totter. As the fulcrum is in the middle to balance a heavy person and a light person all you would have to do is to move the heavier person closer to the fulcrum or move the lighter person further away from the fulcrum. Here is a great example of a class 1 lever. Looney Tunes Class 1
Here is a great example of a class 1 lever.
Looney Tunes Class 1