My Son used to suffer from Armpump quite bad, and sometimes had to really slow down, or nearly pull out of races as a result. But it just seemed to go away over the last 2 years or so (from age 13 to 15). I have not paid it much thought assuming he was just growing stronger, but this does not compute because adults suffer with the pb.
I don't know if it is relevant but the decrease in pump was around the same time he took up drumming, he has a kit at home and plays alot (pardon?)....I wonder if anyone else has found a link with drumming and reduced pump?
It may be a similar excersise may also help, say maybe even if you didnt have a drum kit then just bang some sticks on a log or something!...sure to drive the family mad but may be worth a try.