Don't do endless sit-ups in the hope of toning your midriff. The exercise fell close to the bottom in a ranking of stomach exercises by the American Council on Exercise (Ace).

Do go running or swimming. To get a really flat stomach like David Beckham, you need to reduce body-fat levels too.

Don't waste your money. Expensive, hi-tech fitness gadgets designed to flatten your stomach (such as abdominal rollers and sliders) are a waste of money, researchers at Kansas State University found. If you buy anything, make it a Swiss ball.

Do laugh a lot. It strengthens the deeply embedded transversus abdominus muscle that is the focus of many Pilates exercises and crucial for an ironing-board tum.

Don't starve yourself. The body responds by increasing levels of stress hormones and storing excess calories as fat in the abdominal region.

Do swap your bog-standard swivel chair for a Bambach Saddle Seat (www.bambach.co.uk), which reproduces the natural "S" curve of the spine (rather than squishing it into an unhealthy "C" shape). Researchers at the University of Birmingham recently found it strengthens and tones the abdominal muscles.

And the ultimate exercise? The bicycle move

Lie on your back with your knees bent and feet flat on the floor. Press your lower back into the floor, engaging your abdominal muscles, as you put both hands behind your head (don't pull on your head). Bring your right elbow over to your left knee, and then bring your left elbow over to your right knee in a twisting, bicycle pedal motion. Continue to breathe. Alternate opposite elbow to opposite knee with hands interlaced behind your head in a slow and controlled manner and with full extension of each leg on every repetition. To decrease intensity, keep your knees bent, while you tap your feet to the floor (instead of extending your leg straight out). Repeat for as long as you can.