As requested, I will resume my description of the “best” abdominal exercises (see post from Dec. 11, 2011) according to muscle activity. Below are the four rated highest for working the obliques (the muscle fibers that run on an angle and help make up your waist):
Number one and two are the Captain’s Chair and Bicycle, which I discussed in the post from Dec. 17, 2011.
Number three is the Reverse Crunch: Perform this on your back with your legs in the air. Use your abdominals to lift your hips off the ground. If done correctly the range of motion will be very small. The major drawback with this exercise is how it is performed. I see people using momentum to fling their legs up by their heads. Not only does this minimize abdominal involvement, it also puts stress on your back. Make sure to keep the movement very small and controlled, think of bringing your heels to the ceiling, rather than up by your head. Tight hamstrings can make this hard to execute. If that is the case, try it with your knees bent, but keep your heels close to your thighs to avoid using your legs.
Number four is the Hover or Plank: This exercise is great for the abs and for your back. (See post from Nov. 14, 2010 for tips on form). Those with wrist issues will need to perform this from the elbows. Once you can hold a plank for at least 20 seconds in perfect form you can try these variations:
Maintain the plank and lift one leg without letting your hips shift.
Add a stability ball: Place thighs on the ball, forearms or hands on the floor and hold the plank. To advance, walk out further so your shins are on the ball.
Once you are good with that, you can place your elbows on the ball and plank with your feet on the ground.
These variations are very hard, so make sure your plank is perfect before you advance.