The rock-hard core workout

5. Superman A strong core doesn’t come from endless ab crunches; you’ve got to think 360 degrees here. It’s about working your posterior chain too. Lying on your front, engage your bum cheeks then bring your knees and feet together, with both feet raised a couple of inches off the floor. Take your right arm out in front of you, with your left flanking your left side. Keeping your feet off the ground throughout and switch the forward arm back and forth.