What I've Learned (on youtube) has a bunch of well researched videos. He doesn't go into muscle building per se, but he does go into why you don't have reduced energy and will actually need less oxygen for a given amount of energy if you are in ketosis. Lack of energy is usually the reason given for not being able to put on muscle but that's not the case in practice. But 20% is already low carb, so if it's working keep doing what you're doing.
This is outdated info. Even on keto you can put muscle on just as readily.
What I've Learned (on youtube) has a bunch of well researched videos. He doesn't go into muscle building per se, but he does go into why you don't have reduced energy and will actually need less oxygen for a given amount of energy if you are in ketosis. Lack of energy is usually the reason given for not being able to put on muscle but that's not the case in practice. But 20% is already low carb, so if it's working keep doing what you're doing.