Hi. I heard years ago that toning your trans abdominal muscles (not your rectus abdominal muscles) will create a thin waist. I've tried it several times since then, but never had the patience to keep going more than a few days. However, each time I did it I experienced a rapid and noticeable reduction in my waist. I'm now determined to start daily and I'll report back on the results! This is the exercise I learned:
1. Lie on back with knees bent comfortably, knees together, feet flat on floor, elbows bent with hands close to ears. Keep the small of your back (pretty much) flat against the floor.
2. Stretch your right hand/arm down diagonally across your trunk, across and past (ie left of) your left thigh to the point of 'feeling it' and, at the same time lift your left foot a little. As soon as you do this you will see that you need to raise your right shoulder off the floor. Relax back to the floor.
3. Repeat 2, reversing all lefts and rights.
4. Do sets of 8, gradually building up. (As with stomach crunches, if you go to far you might experience some cramping of the abdominals, so take it carefully to avoid extreme discomfort.)
You're basically doing a stomach crunch, but diagonally from right to left and left to right.
Enjoy!