Ive used the gripmaster and most other grip excercisers extensively over the years. They are very prolific in the climbing industry.
THE thing about them is buying the correct weight. They make 3 or 4 weights of the gripmaster. You should buy the one that you can squeeze repeatedly for a long time! If you get the one where your really struggling to collapse it thats when youll be getting injurys! Its hard to stress this enough.
So go with the softest or the step up from softest.
Or take Buzzs advice, go swing a hammer for a living.
