TA360 GyroBall Gyroscopic Wrist & Forearm Exerciser for Tennis, Racquetball, Squash, Golf, Bowling & Baseball | Low Impact but Feel the Burn GyroBall: Spin-speed determines how hard your muscles work, Strengthen your fingers, wrists, forearms and shoulders, Gyroscope reaches up to 10,000 rpm, LED lights inside illuminate, Simple start with included pull-string. Great for tennis players and all training athletes to give your game that performance boost you are looking for plus protect yourself from Tennis Elbow. Compact and portable, so you can keep in your tennis bag, at work or home. Use daily and start to feel the difference in just a few weeks.