Two weeks ago, I finally got sick of a long-standing problem of mine, so I went up to a trainer and asked a question:
“I seem to have lost my lats. I’m wondering if you could help me find them.”
He suggested wide-grip pull-ups. So, for the past two weeks, I’ve been working in wide-grip pull ups, of all kinds, including underhanded, L Pullups, etc. as a part of a modified Art of Waterbury. I’ve been supersetting them with deadlifts and back extensions, to hit the whole back, at once.
Well, I’ve been checking my weight, and I’ve gained about five pounds, since then. Now, this was really bewildering to me, because I’m standing there in my boxer shorts, looking in the mirror, and I can’t see anywhere that looks any bigger. Not my arms, not my legs, not my chest or shoulders, and certainly not my gut.
Then it hits me. I turn around, and sure enough, everything from butt to lats to traps is a lot firmer and starting to show some definition.
I just gained five pounds of muscle on my back in two weeks. Is that normal and safe? Does it mean that my back is exceptionally weak and needs to be focused on, some more? What else can I do to give this a boost?
Well, I’m no expert, but I can say that I’ve experience a similar phenomenon. My back was one of my weakest points, particularly my lats, as of this past summer. Since then I have been targeting it with some additional isolation movements (like lat pull downs, single arm rows, etc.) in addition to the ‘money’ lifts like pull-ups, deads, chins and seated cable rows.
I too put on a significant amount of weight in a short time frame. Part of that was newbie gains from learning to properly lift in general, but a good deal of that was just my back getting so much extra work and getting up to speed.
Everyone seems to be different, but I’d wager that, particularly if that was a big weak point, the extra work you have put into it has led to a significant amount of LBM gains in a short period of time. Think of it as ‘newbie gains’ for your back, though some of the muscle gain has invariably gone to your biceps and other stabilizing musculature.
In short, while it’s difficult to guess how much of that 5 lbs is all lean muscle mass, and while it’s doubtful that 100% of your gains went to your back, I think it stands to reason that most of that is LBM that you’ve added to a lagging area. Well done 
Entirely possible. It’s hard to beat wide grip pull ups for increasing lat size.
Very nice. Keep doin’ what you’re doin’ until gains stop.