I think some people dread our obsession with Double Unders. Unfortunately you cannot condition or strengthen your way out of it.
Its a function of practice! Here are some practice concepts from Bryant Powers
1) nothing changes from single to double under
2) maybe a bit higher jump
3) stay on balls of the feet
4) don’t pike or donkey kick
5) circle from the wrist
6) practice jumping from the same spot
and some ideas from an old geezer called Andrew Stemler
Higher jump, big chest, try taking your shoes off!
We will make the ultimate Double Under Video soon, but for now, I hope these will help you improve your practice.You have to buy your own rope and “own it”!