Is it good to work only on the circumferrence, and if so, what excersice woulb be the most efficient one?
Do you want length?
The consensus on gaining length is that it should be gained first. Girth (circumference) should be worked on after gaining length.
When you say first do you mean because attacking girth first may hamper ones long term ability to gain length? Or is it simply that length is easier to gain, and the preferred goal of most men, so that should be handled first?
I would imagine that increasing girth makes length somewhat harder to gain, from a strictly engineering viewpoint. Structural strength (which dictates how much force is necessary to stress it) is proportional to cross-sectional area, and all that jazz. Unfortunately (?), I myself have been gaining girth purely by accident just from my easy newbie routine. Well, I suppose their are worse fates than having a thick penis. :)
The standard theory for the girth thing is the rubber band theory, which is pretty much what BibBob described.
My personal view is different. I think that working girth can aid length gains because applying a stress in an alternate direction can prevent the structure of the penis building up too much resistence to gaining length. This is also based on structural strength and attempting to alter it to gain.
Its probably worth following the rubber band theory first, cemented girth can’t be undone.
Wait, my babble made sense? Something’s not right with the world.