Don’t forget the core!
When working out to be able to jump higher and in general become a better athlete, don’t forget the core, meaning you hips, stomach and the areas around there.
For every practise, be prepared to do at least two different kinds of either sit ups, crunches of ohter stomach related ecercise.
Do at least 200 situps per day. You can also put weights on you ankles while lying down, take a secure grip with your hands behind you head, and begin to lift your legs, them being straight, at least ten times. You can also alternate by doing them a little sideways.
On top of the do at least 50 crunches.