Exercise & Fitness: Powerball Blue Pro 250 Hz - Blue Exercise Ball Hand Exerciser Perfect for golfers, musicians, squash, tennis, fencing, basketball, badminton, archery, cricket etc. Use for rehabilitation and relief from carpal tunnel syndrome and RSI. 250Hz Pro Powerball comes with a digital speedmeter/counter. Just the size of a tennis ball and weighs under 300grams. Ages 14 years and up.