In San Antonio, tennis playing Texans aren'nt forgetting to do their cardio workouts. In fact, some San Antonians are combining tennis with a structured cardio workout, says Wendy Rigby of KENS 5 Eyewitness News. Cardio tennis keeps your heart rate in the aerobic training zone for an hour with short bursts of high intensity. "It's a way to play at the same time as exercising. A lot more fun than the treadmill," cardio tennis student Elizabeth Rogers told Rigby.