Do this exercise any time you want: Suck in your belly button and squeeze your butt as if you're pulling up tight jeans. It helps with posture and strengthens your abdominals.
Exercise Videos; Beggining, Intermediate, and Advanced Core Training
Done without equipment. Follow the links to download onto your computor.
http://www.oprah.com/tows/pastshows/...061102_b.jhtml