Plank Superman on Hands/Knees

Kneeling on your mat with hands on the ground, hands are shoulder-width apart and knees shoulder-width. Gradually extend your left leg (lifting your left heel) until its straight and at hip height. At the same time lift your right hand off the ground and straighten your arm (lifting to shoulder height). Aim to hold this final position for 1-2 secs before returning to the start position and repeating. Complete the 10 reps and repeat on the alternative side.  Aim to keep your hips square throughout the movement.