http://www.t-nation.com/free_online_article/sports_body_trai...
It claims that your body can only synthesize about 2 pounds of dry muscle mass per month.
34 pounds in 28 days is roughly a pound of muscle per day. I've always found myself wanting more evidence to back that up, or even just seeing more examples of people saying they've done that. The closest I've heard to getting that kind of result are people who add drinking a gallon of milk in addition their regular diet, and even then they gain a fair amount of fat in addition to muscle and it's way less than that number.