Refer to my blog about Monday Hangover. One of my favorite ab exercises is the criss cross. If you do ten as described there and ten with your legs straight instead of one leg bent and go back to bending one knee in for regular criss cross exercise for ten you will feel a nice burn in your abdominal area!! Keep your rhythm smooth and even. Remember the more tension you feel in the body when you perform an exercise, the less you will benefit. Control, rhythm, and feeling length in the body while you perform any exercise will give you the results you want.