OK...
once you've got "it"....try to focus on RELAXING when you can (i.e. smooth sections, over jumps, etc...) and remember to BREATHE deeply. Try to not keep a "death grip" on the bars....Breathe, relax, breathe, relax, breathe, relax--repeat this mantra....
Now, having said that...do not give up on prevention! There ARE many things you can do to mitigate the effects of armpump!( I currently ride a 500--I know!!!
) first off, I agree with the above posts--Don't underestimate the power of water--hydration is a key factor. I am not talking about drinking Gatorade (et all), the day of the race--I am talking about on a CELLULAR level--drink "tons" of water starting (at least) 72 hours before your race. Next, get plently of potassium in your system--potatoes, bananas, supplements etc...I also think armpump has more to do with circulation than "strength"--try to loosen up (i.e ride HARD in practice, do excercises before you moto, etc...) before the race to get your blood "flowing"....
I still get armpump real bad on occasion and the other times I am not affected by it at all, so by no means do I have the answers....just what works best for me...hope this helps....
Also, you mention "t"not affecting speed, but control...watch this--if something is affecting your control, it canaffect your speed in a MAJOR way! By that I mean, if you "pumpup" real bad it is best to back off and come back to "fight" at a later time--most (if not ALL) of my "big" (read: injury inducing) get-offs have occured when I was pumped and crashed as a result of something I normally would have "saved." Just a caveat....
Best of luck!
Gripper
'99 CR 500R
Vet Int-B MX