How many times you can train a muscle group depends on the amount and intensity of the training you do. Anyone could do 50% of maximum for a set of 5 seven days a week. On the other hand, the ridiculous 25 total sets divided between 3 or 4 exercises for a single muscle group workouts cant be done often, most who do them train a muscle group only once per week.
So the real question shouldnt be how many times you CAN train a muscle, but how many times SHOULD you. I believe that for the vast majority of people, 2-4 times is the right amount, with 3 being great for most. Volume and intensity can be handled in such a way as to allow this. This usually involves 3-5 hard, heavy sets, but not taken to failure of 3 or 4 heavy exercises per workout, things like squat, press, bench press, deadlift, rowing, chins, cleans, etc.
JS