Is Madonna flexing her muscles at her former trainer, Tracy Anderson? The Material Girl recently announced a plan to open a series of Hard Candy Fitness Centers worldwide, where, sources tell us, “she’ll be closely involved in developing dance-based workouts.” Her first gym opens in Mexico City this month, with plans for Russia, Europe and eventually the US. Sources said the plan may have evolved after Anderson famously had a falling-out with Madonna over Anderson’s capitalizing on the superstar’s name to build her fitness empire in New York and LA. But a different source close to Madonna said: “I don’t think she even gives Tracy a second thought. It’s a natural idea for her to have her own gym. This is a business plan that she has been working on for some time with her business partner Guy Oseary.” A rep for Madonna declined to comment.