Once you understand how to bounce and jump while using the bocks, getting more hieght is easy, I didnt push myself at all on my very first jump and ended up being a good foot into the air! Odd as it my sound, keep your legs straight and use your heels, not the balls of my feet for a jump/bounce and let the springs do all the work.
Its definantly toned my muscules out, my abs aswell.
Its a great work out, for only a few hours worth of bocking around, Its like I've ran a few good miles without all the hard agro needed (still works up a sweat mind).
Jumping without the bocks on has certianly gotten higher since using them, It might only be a few inchs, but I've noticed it several times... mainly because Im banging my head on the light shade and I never used to do that.
Even if you wernt to use bocks for sport, its defianantly a good work out and fitness option, on the plus side... they look awesome