DETROIT – The 8,000 employees who work at the General Motors Renaissance Center (RenCen) in Detroit will soon have a new place to work out without leaving their office building. The YMCA is opening a 12,000-square-foot health and fitness center on the ground floor of the RenCen, which houses 6,500 General Motors employees and 1,500 other employees. The center, which will feature cardio and strength-training equipment, two group exercise studios, group cycling, personal training programs and lifestyle improvement programs, will open early next year.