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The first thing that pops into our minds when we think of Gwen Stefani is her incredible abs which she regularly displays much to our grievance. The key to achieving a flat, washboard stomach is repetitive exercises combined with a low fat diet. Gwen's trainer has her lie on her back on a fitness ball with her legs in front, making a bridge. Then she holds a medicine ball behind her head, by her right ear before curling her body up and bringing the ball diagonally across to her left knee. Try repeating this exercise ten times before swapping over to the other side and you'll soon notice a difference.