[QUOTE=DannoXYZ]Just don't do any upper-body exercises and the muscles will atrophy to be the minimum needed for the exertion level. This takes a lot of time, months, years.
+1
Last year I was doing tri's and spent a lot of time working on my upper body/swimming muscles.
I used to do tons of high rep weights on the pecs, lats, triceps, etc.....
I quit that about six months ago to focus on cycling only and I'm amazed at how much upper body tone I still have. At least it's not bulk though. Just lean mass.