My husband has been on a low carb (typically 30g a day or less) for almost five years. The initial weight loss revealed a long suspected almost total absence of any muscle. (Yes, I'm exaggerating but you know what I mean.). He then started weight lifting, with the aid of an instructor. While, in his late 60's nobody is expecting a six-pack and a Mr Universe build, he has built up very good muscles and strength for his age. You don't need sugar/carbs to build muscle.
Sally