I knew it. No, I think was Arnie was stoned when he compared getting a pump to cumming, he was into that in the 70s.
Oh yeah, the context for the rest of you:
Spoiler
The feeling you get while pumped is more like a hard-on on the muscles, its about blood flow making something get bigger after all, so yeah the feeling of tightness is similar. There is no blowing up like Arnie said, unless you tear a muscle, its a hard-on without a "happy ending". But I suppose Arnie can say one can get his mind goes off problems through both ways.