Hi, I just wanted to share something with you guys, I hope you find it useful.
Earlier on today, I was going through some old stuff I had and I found one of these; http://www.nsdpowerballs.co.uk/image...ure-Series.jpg
I hadn't used one in years and years, but I picked it up and started using it, and it felt brilliant. I had had a bit of a sore wrist recently, probably from playing bass too much actually, and it eased that really effectively, and felt like really good exercise for my grip muscles in my hands.
A little bit after doing this, I decided to play bass again for a while. Good god, I have never played so well and with so much stamina in my life. It was like having had the best warmup possible. My grip was ridiculously solid, but easy at the same time. My plucking fingers were completely relaxed too, while still being able to pluck faster and more consistently, and for much longer, than I had ever experienced before. I honestly felt like I had added years of experience to my playing.
Also, aside from just warming up, they also build muscle in your arms and increase your stamina too. I'm going to be using mine a lot from now on, I think. Also, on a side note, I think they're advertised as being helpful for things like RSI, which is a pretty common affliction for bass players with imperfect technique. If it helps avoid that in the long run, then that would be an incredible help for a lot of people.
And before you ask, no, I do not work for the people that make these haha. I was just stunned by how much it helped me.