Indoor cycling fitness chain SoulCycle Inc filed with U.S. regulators for an initial public offering of common stock, underscoring the rising popularity of boutique chains that cater to specific workout methods such as spinning, yoga and barre. SoulCycle was founded in 2006 as a single, 31-bike indoor cycling studio in New York City by former real estate broker Elizabeth Cutler and former talent agent Julie Rice. The company on Thursday said Chief Operating Officer Melanie Whelan took over as chief executive in June.