My friend is training with me doing calisthenics. He is consistent with his training and diet, gaining weight when weighed at the end of every week. I did a little bit of research for him as to why he hasn't seen any results. From my research I've seen some academics saying that if someone is a non-responder he can change up the reps, volume, etc to see results. But some others say that in studies they found out that they have an inflammatory response to weightlifting and so more volume will do them harm.
Is this a medical issue he is facing? Is that inflammatory effect genetic? What I can do to make him happy and grow?
Sorry for my grammar. English isn't my native language. Thanks.