stretch before you play. religiously.

The backs of my hands some times cramp and maybe a finger or two...

how old are you? What kind of work do you do for a living? Do you spend a lot of time on the Internet (keyboard)? Have you ever sustained an injury to your left arm? If you live in a place where you drive on the left side of the road, do you have your arm around your girlfriend or doggy a lot when you drive?

A lot more info could be pertanent to your problem, but you get the idea...

Are you playing while sitting down?

Are you fretting many notes quickly?

A multitude of things can cause cramps. Most commonly over excursion. Like Adam said try stretching first. When you work out you dont just go grab weights and start lifting. You warm up and then stretch first. Another thing that can cause cramps is dehydration. So if you are a big drinker you may just need a Gatorade or something like that. I cant remember exactly why, but something to do with the lack of electrolytes in your body. Even if you dont drink are you getting enough water? Also how is the action on your bass? Mine was a bear to play. Mine has issues a hump in the neck that cant be taken out. But, if you are having to squeeze the Hell out of the bass to play that is going to take a toll as well. Youre going to have to do some trouble shooting to find the cause.

Dave

Some problems can be a symptom of not getting all the nutrients you need in your diet too. Drinking lots of sodas can lead to dehydration and leaching out the nutrients you need.

As Dave and others said, might be several things to check out, action of the bass, setup, etc .... but all good things to keep in mind for your health and well being.

Strengthen your fingers,hands and wrist. You can buy one of those at GC or Sam Ash or any music store. It will help. D

Yo Ian,
Welcome to the Best Darn Bass web site in the known Universe...ActiveBass.Com! We are are Happy that you are here with us!!
What you should do is stretch before and after you play!! Also, Drink your share of H2O...Water! Eat well. :^D
Black Hawk