it's actually not too much strength. although it's good to have strength, most of the spring upward comes from your hips. i suggest you learn handhops or forearm hops first to understand the idea of using your hips to spring yourself upward.
that's how it seems, but if you think physics, the legs are barely pulling on your body. they're going up and down so that the hips can go up and down. how else do you think people can do handhops with their legs open the whole time or closed the whole time.
for pretty much every move in bboying, the power comes from the hips.
and then kick your HARD enough up and push up from forearm all your strength on your hand and then push
