Warning: not for those with back problems! so I stumbled upon the 30 day plank challenge when trawling through google for a good way to trim inches from my whole body. It's one simple exercise. Not overly exerting and the challenge starts at holding the position for 30 seconds and then gradually works up to 5 minutes by the end of the 30 days. this exercise tones your stomach, arms, thighs and chest. Image search "30 day plank challenge" online and follow the instructions you see! I challenge you to plank every day for a month!