Used by astronauts and professional athletes to tone and strengthen upper body muscles, this is the rotating gyroscopic dumbbell that starts at the touch of a button. Holding the tennis ball-sized device and rotating your wrist maintains the rotation of the gyroscope to spin up to 15,500 rpm and provide up to 45 lbs. of torque resistance to strengthen the wrists, biceps, triceps, and deltoids. A study performed by Southern Utah University proved the gyroscopic dumbbell increased maximum handgrip strength by an average of 11%. The low-impact exercise can also increase the range of motion in hands and help rehabilitate carpal tunnel and tennis elbow injuries. The included base spins the internal gyroscope to the optimal speed in 10 seconds and the dumbbell's integrated tachometer measures and displays the current rpm, highest rpm achieved, and total number of revolutions. Base requires two AA batteries. 3 1/2" H x 3 3/4" W x 4 1/4" L. (1 lb.)