contrary to everyone saying you are full of crap, I agree that supplements can help arm pump. Well, vitamin C specifically. It's a fact that vitamin C prevents lactic acid buildup. I do not get enough vitamin c(dont drink milk), and most people dont get enough either. When I started taking vitamin C supplements my arm pump went away. I know it's not my riding style because if I forget to take my vitamin C the pump comes right back. I usually take one or two 600mg vitamin C's a day. Hope this helps, although most of you will probably just say I'm full of it. FYI I used to lift weights heavily and used to get "arm pump"(forearms locked up). That is when I discovered the vitamin C, it works for weightlifting also.