I forgot to mention there are a lot of variables to considers, including your genetic limits (how far you are from them), your bodyfat%, your current mass, etc. Obviously the lower your bodyfat, the more apt your body is going to be to burn up muscle, which is why it's so hard to reach a very low bodyfat% naturally at any kind of reasonable weight.

Here is a good read on P-ratios by Lyle McDonald, also a good thing to consider. And on the same note it helps enforce the fact that people should wait untill they are under a certain bodyfat% before they start bulking considering leptins effect on lowering testosterone, raising cortisol, etc..

Here is the article: http://www.bodybuilding.com/fun/core3.htm