We dare you to try to hold this ball for more than a minute! Used by doctors and therapists worldwide! Dynaflex Pro Gyro gyroscopic exerciser is an easy, relaxing and extremely effective way to strengthen your grip and improve coordination without strenuous exercise! Whether you want to get the edge in any sport that requires control and a strong grip or simply strengthen your grip, Gyroflex Pro gets the job done. Just pull the starter cord and it starts to spin at speeds more than 10,000 RPMs and generates up to 38 lbs. of torque resistance - it's a real workout! Also features variable resistance and durable design. "I severed a tendon in my wrist years ago & have struggled with a poor grip ever since. After using Dynaflex for one month, my grip has returned and my finger mobility has improved." Bob S. - McAllen, TX