I thought I'd drop in a Hi. I'm still on the Jujitsu! As a Black Belt, soon hope to be 2nd Dan Black Belt; I am inclined to post this for all newcoming enthusiasts.
Need I mention that in studying a martial art, purely for the sake of combat, it's important that you know what you are doing to your body, during any exercise you might feel inclined to do at the gym. Don't aim soley for strength, aim for tone, but slowly build up your strength during the work-out process; I say this because I know alot of great artists who have lost speed through the weight of the muscle, in comparison to the people who have let their muscles naturally tone up and build.
It is vital that you optimise your muscles in Martial Arts in any case, not only for them to be strong, but for them to deliver blows quickly and with efficiency, and this does not mean big muscles are a bad thing!
Yet target the wrist muscles, triceps, pectorals, and abdominal reigons in particular. I cannot stress how much more effective a stronger wrist is when delivering blows. With perseverance the tonage should come naturally anyway.
Yet the extra effort is not neccesary, in the slightest, for your first years of any martial art.
My Golden Rule: Never Be Hesitant