Ugh, so much wrong with your replies in this thread, it'll take a while to break this all down for you.
1. First of all, you most likely have your terminology screwed up. "Overtraining" is primarily a central nervous system (CNS) phenomenon and not something related to individual muscle fatigue. It's a result of your CNS being unable to recover from the load/volume of exercise you do, which leads to symptoms such as fatigue, loss of motivation, decreased immune system response, etc. Training the same muscles every day in and of itself does not lead to overtraining. The typical olympic weightlifter, for example, trains ~5+ days per week using the same exercises over and over (clean, jerk, snatch, squat). Many strength training routines involve squatting 3 times per week, not to mention the overlap with deadlift, power cleans, good mornings, etc. In fact, this constant repetition is part of almost every athlete's routine: many runners run every day, soccer players play soccer every day, and so on. As long as these athletes are recovering enough - that is, getting enough sleep, food, rest days, etc - they will not see overtraining symptoms from using the same muscles/exercises over and over.
2. Perhaps what you really meant was that training the whole body multiple times per week might be inefficient because your muscles might not recover enough by the next workout. This is the assumption of most bodybuilding split routines but in reality, it is a pile of BS. Muscles are able to recover surprisingly quickly and you don't need to be 100% recovered to train again; every single high level athlete routinely trains while sore and tired. However, if you understand the recovery curve, you'll realize the benefit to this: as part of the recover process, muscles will "supercompensate" in response to training, becoming stronger than before training. The sooner you can train again, the more you can take advantage of this supercompensation, and the more weight you can lift. Repeat this cycle many times and, much like compound interest, you get very rapid gains. Supercompensation happens 12-48 hours after training, depending on genetics, diet, rest, etc. Therefore, waiting a full week before training the muscle again (as you do in a split routine) is VERY inefficient because the wasted time allows the muscle to lose some of the supercompensation, making for slower gains.
3. Obviously, there is a limit to how frequently you can train and how heavy you can go. A lot of it depends on genetics, but in general, as you reach the advanced stages of training and are moving seriously heavy weight, it takes longer to recover from exercise. Only a few people on this forum are anywhere near that stage. For the majority of people, the most efficient training approach is to go as heavy as you can as often as you can for the entire body. How heavy and how often, of course, depends on goals, genetics, diet, etc... But it'll be far more often than once a week for just about everyone.
4. My personal routine involves heavy lifting (squat, deadlift, clean & jerk, snatch, press) followed by a CF metcon (can consist of anything, including more lifting, bodyweight exercises, running, etc) ~3 times per week and endurance workouts (usually running or rowing) followed by skill work (typically gymnastics moves such as pistols, muscle-ups, etc) ~3 times per week. In other words, as I said before, I'm at the gym 5-6 times per week and every single workout typically trains the entire body. And shockingly... I'm not overtraining and still making progress.
