There’s all kinds of ways to isolate and work out just the muscle groups you want. Over the years, we’ve seen them all, but it’s the first time we realize a neglected exercise: the hand extensors. You’re likely familiar with those Hand Grip Strengtheners, which rely on you squeezing to develop the muscles of the forearms. But the opposite of squeezing, extending your fingers, seems to go largely ignored. That’s what the Xtensor Hand Exerciser is all about. Insert fingertips in rubber rings, and gain some strength with the resistance provided. We can’t really tell you why you would want to develop that particular set of muscles, aside from maybe being better at flinging stuff off your finger tips. Or maybe relieving ostheo-arthritis symptoms, as the makers suggest. It’s $30.