Bring yourself to the ground and enter a high plank position with your hands directly under your shoulders and your legs extended directly behind you. This is your start position. Keeping you core braced, bring your left leg forward until your knee is by your armpit with your left foot flat on the ground. Gently lift your left hand from the floor and bend your arm so you can drop your left shoulder towards the floor slightly. Pause here and then reverse the movement and reach your left arm up, opening your chest towards the sky and fully extending your arm. Pause in this position and then return to the start position. Repeat the same sequence on the other leg. Repeat this alternating pattern for the required number of reps (or time).