look up any word, like blumpkin:
 
1.
A male definition. Adding muscle mass or weight by going to the gym frequently and eating a high-protein diet.
Q: Dude, why are you eating so much meat?
A: I'm trying to bulk up.
by Stud April 11, 2005
 
2.
vomit - British army slang
After eating the concealed pizza, I grabbed the bog and proceeded to bulk up
by Raeburn June 11, 2006