Royal Oak resident Ralph Colone, viagra generic 64, has played tennis for two decades. But it’s only in the past two years that the sport has truly sent his heart into a flutter. That’s when Colone first heard of cardio tennis, a growing fitness trend. More than a million people have tried it, said Michele Krause, the national cardio tennis manager for the Tennis Industry Association. Cardio tennis is just what it sounds like — a cardio workout on the tennis court, complete with pulsating music, warm-ups and cool-downs, and an absence of line judges or confusing score-keeping.