I think you're asking if the arm you masturbate with has more muscle than your other arm.
Naturally, you'd jack with your dominant arm (right handed --->right arm, left handed---->left arm). One arm would be stronger with or without masturbating, just because you use it more. Since masturbating is a motion, and you are using muscles, it might do a little but barely anything. You wouldn't see a huge difference in how your arms look.
If you want arms, don't jack, lift weights like I do!