Does anyone know how much weight you are pushing when you're doing pushups? I'm just curious. There has to be some sort of formula maybe?

Around 60-70% of your body weight is a good rule of thumb.

Hope that helps!

-Andrew
http://www.Modern-Athlete.com

Tell you whats harder, crazylegs told me to do this

Put three chairs in a triangle, feet on the back one and one hand on either of the front chairs. Do a pushup and go right down and up again, its much harder!

Just for your general intrest, here are a few you may like to try.
"
kung fu push up.
lay flat on the floor and put the palm of your hands on the floor so that your hands are inline with your belly button, fingers facing up or out (however is comfortable). make sure that when you pushup and down your elbows are tight against your side. This is great for triceps and takes all pressure off you shoulders, so its good if you got shoulder strain.

streched push up,
bring your hands closer together but just above your head the higher you go the more impossable it gets. this really works your abs to. I can do 300 normal push ups, but ony 20 of theese bad boys!!!!

lizard push up.
One hand low and one hand high. on every push up you gotta get high enough to swap hands. keep good form and dont rush.

step push up,
hands in normal position, but one hand is on a step 8-12inches if pos. do your push ups still going as low as poss, this makes it harder for the lower arm as its taking more weight.

2step push up,
take 2 steps this time and place them just over should width apart, do one step push up, then bounce over to the other step in one go, so your doing the mirror image of what you just done.

decline push up
works your shoulders, put your feet on something, a gym ball is best, cos you learn balence. also good for abs.

"

Yeah, these are my favorite. What's fun is when you're done, hold the plank position, and when you get too tired, drop your feet but as you're going down, tuck them [your legs] in. Hold. This is gives you a great full body exercise, cause you got the hip flexors, abs, arms, and back all working to hold you.