Get arm pump? do this 2 ur bike for a quick fix:
roll ya bars in the clamps back, doesnt have 2 be in ur lap like ricky carmichael, but jus so they ar parallel to or behind ur forks. stops u reaching for the bars n also dont have 2 grip as hard as the front end becomes less twitchy, and also benefits many riders in cornering
then raise ur levers so they are either parallel to the ground or higher, this stops u griping the bars and tensing up your forearms
Then the cure: get fit! RIDE!