Research lists the bicycle, captain’s chair and the stability ball crunch as the top three exercises that work the rectus abdominus. I want to be clear that these are not necessarily the best exercises for your body. Despite all our emphasis on working the abs, there is no real evidence that strong abdominals can prevent back pain. In addition, most of the exercises that were tested involve some degree of the controversial spinal flexion (see post from Nov. 7, 2010). However, if you choose to do them, there are some ways to make them safer.
The bicycle is performed on your back, the legs bend and straighten close to the ground, and the torso rotates, bringing opposite elbow to knee. The main problem with this exercise (in addition to the spinal flexion) is the momentum most people use. They pump their legs wildly and let their hips roll from side to side. You can make it safer several ways: First, slow it down (this is true for almost all exercises), you will rely less on momentum and target the abs more. Keep your hips on the ground. You can also eliminate the flexion by leaving your torso on the floor; keep your spine in neutral (do not let your back press down or come up), and SLOWLY, alternate straightening the legs.
The Captain’s chair uses piece of gym equipment. You support yourself with your arms, dangle the legs and pull the knees up into your chest. This can be a great exercise; the major danger comes from performing it with momentum. It can also be problematic for those who do not have enough upper body strength to maintain the position. You can make it harder by slowing it down, and by performing it with straight legs.
The stability ball crunch is just what it sounds like. You lie on a stability ball and perform an abdominal crunch. It does involve some spinal flexion, but the ball helps keep it to a minimum. Make it safer by supporting your head without pulling on your neck. You can make it harder by moving out, so more of your upper back is off the ball, and of course, by slowing it down.