It is important to recognize that core does not just mean our front. The muscles of the back are just as important for balanced posture. The super man is a fantastic and functional exercise for our posterior chain (muscles of the back). When done properly this is quite a challenging exercise. You want the trunk to stay still whilst the arms and legs move smoothly.
Start in a neutral spine, hands under shoulders, knees under hips. Engage the core.
Reach the opposing arm and leg out so that they are parallel to the ground. Your goal is to keep the shoulder away from the ear and both hips even to the ground. Be careful not to attempt to lift the leg to high. This exercise is all about alignment and length of the limbs and keeping the core active.