Mirs adding muscle because apparently hes obsessed with Lesnar he says it. That takes a confident man to go on TV and say hes obsessed with another grown man.
Lets see if Mir strikes .. Has to get ready to strike with Lesnar next time after all, Congo should be a good place to display that world class striking he picked up in the last year.
It is totally possible, especially for a big guy like Mir to put on that kind of weight. Just over 3lbs a month, and some of that weight is not muscle, as you can see in the picture.. Mir is a well proportioned big guy. Just from that pic, looks like he has worked pretty seriously on his arms, which may mean he has been working on his back very seriously *hopefully* Back and Legs, are muscles that will release more natural growth hormone, and those are two groups of muscles that will help a fighter like Mir against a guy like Lesnar in a standing clinch and takedown defense. Picking up the skillset to defend against a great Lesnar shot is something on a different level though.
Again, with the kind of conditioning program these guys follow, putting on muscle in a short period of time is extremely hard, naturally. It's not as if he's a bodybuilder now and just hitting the weights and eating like a pig. Even bodybuilders don't have gains like that, that fast without juice anyway. But whatever.. who knows.