Come into a half-kneeling position with your left leg elevated and your torso upright. Extend your left arm directly out to your side so your hand is level with your shoulder whilst your right hand is extended by your side with your palm facing in. Make a fist with your hand but keep your thumb extended. This is your start position. Stabilise your body by squeezing your opposite fist, engaging your abs, pressing your shoulders down and squeezing your glutes. Keeping your right arm locked out, raise it straight back behind you and up towards your head. When you hit your end range, rotate your palm out so it's facing away from your body and bring your arm up over the top of your head. Keeping it fully extended, bring it down directly in front of you until you are back in the start position. Try not to compensate for lack of range in your shoulder joint by moving your body. Aim to keep your body still throughout the movement. Peform the same sequence in reverse. This counts as one rep. Repeat for the recommended amount of time (or reps) before changing to the other side.