I'm a big fan of the treadmill, mostly because it does such nice things for my abs and obliques. If I do a consistent treadmill program where I alternate a walk/jog I don't even have to worry about crunches or other ab exercises. If you move your arms while jogging on the treadmill you are forced to twist at the waist and over time it will give you some amazing definition in that area. Well, as long as you keep your diet clean as well. Diet is about 75% of it, especially when it comes to the abs!
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Inside me there is an angel whom I am constantly shocking...Dolly Parton