Start on your hands and knees, with your hands under your shoulders, and knees under your hips.
Keep your back straight and your hips in a neutral position.
Drive the heel of your hand into the floor so that your shoulder blades flatten against your back.
Lift one arm up and keep your elbow straight.
Ensure your body and hips do not move throughout this movement.
With your arm horizontal, move it from this position, out to the side then back to touch your hip, and repeat.
