This Pilates move is far better than endless sit-ups for strengthening your core muscles. Lie on your back, knees bent and feet flat on the floor. Take care not to flatten your back into the floor or over-arch - it's important to maintain the natural curve of your spine. Lengthen your arms away from your shoulders, parallel to the floor, pulling your shoulder blades down your back. Curl your head and shoulders off the floor, inhale and exhale for a count of five per breath. Draw your navel towards your spine throughout the move but don't let your abdominals push upwards. To make the move a little more challenging, lift your feet off the ground, keeping them in line with your knees and parallel to the floor. Hold for up to a count of 100 if you can manage it.