What is a more colourful way of saying someone who wants to gain weight, increase their muscle size by going to the gym?
He has been regularly visiting the gym in hopes of ___
Can I say ‘packing some guns’ here?
Which means getting
Well defined muscles
It also doubles up as getting drunk.
If I understand your question correctly, you may be asking about one (or possibly both) of the following:
From how I interpret your question I am going to choose to address number 2. For number two I think it's pretty standard to say:
building up muscle
Has been regularly visiting the gym in hopes of building up muscle.
To become bigger, stronger, or bulkier: The actor beefed up over a couple of months so that he could play the part of a boxer.
(The American Heritage® Dictionary of Phrasal Verbs)
pack on size
There are millions of guys - commonly known as "hardgainers" or "ectomorphs" - who will never, ever pack on size.
pack on meat
How about the word "jacked" ???
It seems to me, that compared to the to the other choices, "Jacked" sounds the must hip and evocative. I would imagine a magazine writer, writing an article and needing such a word, would opt to pick this word over the other choices posted (so far.)