I am a small person and also needed to gain muscle mass. I had abused my body by following a low carb diet, and my muscle mass was just wasting away. It was like my body was eating me.
Once I started making changes in my diet and following the ML protocol, my body just seemed to know what to do. That was a year and a half ago, and as my health has gotten better I have been able to join the gym and feel and look so much better.
Maybe that is all one needs to do, follow the protocol and let the wisdom of your body do the rest.