@EMPIREMIND - you are correct. While I think Powercage is right as well but I think there is A LOT of oversimplification, misinterpretation in this thread.
The study doesn't really discuss the antioxidant status of NAC. NAC increases an antioxidant - glutathione - but it is NOT glutathione.
The theory that is being infered here, and I can understand why, is that increased antioxidant levels are hindering the signaling pathways that trigger adaptive response. Maybe...
The theory we like to believe is that we exercise and this causes muscle damage and we repair that damage and then add a little more. But this is a bit naive. Damaged tissue is often weaker than the original tissue, not stronger - ask any surgeon.
Finally, there is evidence in the studies I posted that show that ROS actually causes muscle wasting. Granted, in the elderly, but if this secondary stress played a primary role in adaptive response then elderly people with their high levels of ROS and reduced glutathione levels wouldn't waste away. Powercage is actually pointing out here that there is an optimum level or antioxidant capacity and he is correct...but it is more complicated than "you will get huge" or "you will waste all your gains". It isn't an on/off switch.
It is nothing but foolish to think that if you take NAC and then go hit a brutal workout session that stimulates muscle growth, that all of your gains will be wasted. The reduced effect will be minimal.
It is like saying that drinking too much water will keep you from tanning.
Your body will respond if it has to.
And I use the methionine analogy because methionine is known to avtivate mtor and igf-1 and is powerful enough at this that it is promoted as a driver of aging and methionine restriction has been proposed as a means of anti-aging.
Yet, methionine and cysteine are the two sulphur containing aminos, botg increase glutathione, and methionine itself is used to make cysteine. So, if this is so direct, how does that work?