RE: Once a week enough????
All depends how hard you work them. i.e. how much resistance you use and how long you've been doing it. Any muscle will plateu off when it gets used to a stimulus. My training consists of approximately 20 sets per muscle group. (4 exercises, 5 sets of each), rep range depends on which phase i'm in. This is sufficient for me. If your making gains then its ok, if your not something needs to change.