Heart rate monitors:
While you don’t have to wear a heart-rate monitor, it helps to ensure a safe and healthy workout. Also, it helps the tennis pro to know who needs to be challenged and who might need some rest a bit. At the end of the class, the monitor will tell you what your average heart rate was, how long you were in your zone and how many calories you burned. Some facilities loan them, but it’s a great training tool for any athletic activity, so you might want to invest in one for yourself. Info USTA