Lack of the arch in the foot is medically described as pes planus, a common condition and usually not painful. All of us have flat feet when we are born, and the development of the arch usually takes place during childhood. There are two types of flat feet: flexible and inflexible. If your foot is flat when it's in a neutral position but the arch forms when you stand on tiptoe, it is considered a flexible flat foot. If the arch is missing when you are standing on your toes, it is inflexible and may be because of tarsal coalition, a condition where two or more of the small bones of the foot fuse together. It usually can only be confirmed with X-ray.
Perhaps the best exercise for keeping the arch healthy is the "towel scrunch." With time and decreased demand on our feet, the small muscles become weaker. Since we are no longer jumping or skipping as we did when we were kids, the muscles lose the ability to give our feet the spring they once had. To strengthen those muscles, start out barefoot in your favorite chair and spread a small hand towel on the floor in front of you. Place the ball of your foot on the edge of the towel closest to you and, reaching out with your toes as far as you can, grab the towel and scrunch it back toward you, bunching it up under your foot. Keep reaching out and grabbing more towel until you run out. At the end of each scrunch, hold the contraction you feel in the arch for just a second before releasing. Do three sets of scrunches with a short hold at the top each day.