Start standing in a wide stance position, with your knees slightly bent.
Transfer your weight over to your right leg, bending the knee so that your butt is slightly lowered into a squat.
Straighten your left leg out to the side, and lift both arms up above your head.
Tightening your core muscles, bring your left knee up to your chest as though you were kneeing an opponent. At the same time, bring your hands down to meet your knee.
Return your hands up above your head, and left foot back to the ground – don’t transfer weight into your left leg, instead repeat the knee-up motion at a rapid pace.