Normal tremolo arm pressure?

If you're watching an experienced guitarist, i.e. Alex Lifeson, pushing around a whammy, chances are he makes it look MUCH EASIER than it actually is. I was surprised myself early on how hard it was to move the thing around and push it in, but it just takes practice. Eventually, your fingers and lower arm will grow stronger and you'll be able to do it just as easily as Lifeson makes it look.