First of all - soreness has no correlation to the effectiveness of a workout. It is generally a product of low frequency and high volume training. Being sore is neither good nor bad - although it can impede another workout which is generally bad. Phenomenal gains have been made on programs where athletes almost never get sore. This is accepted as fact by every researcher and strength coach in the world - DOMS has no correlation to either a good or bad workout.
As for recovery - do you really think muscles recover in a few days? Maybe a week right? Nope, look up complete tissue remodelming, it can take well over a month from a single bout of weight training if I remember correctly but regardless it is far longer than any split in use. Bottom line you are almost always training in some type of recovery deficit.
Where did the 1x per week come from? It came about because BBers started talking about overtraining back in the late 1980's (at the time just previous to this the common workout in the muscle mags was 3 on 1 off and I remember a fair amount of AM/PM days too). A few guys began to notice that if they took time off they came back stronger. They then thought that this was because their workouts weren't optimally spaced and timed. This is the essense of single factor theory or Supercompensation where you go in the gym and work ultra hard pushing your muscles to the point of full exertion (welcome to the training to failure school). Then you retreat quietly and heal up slightly stronger. Just after you've gotten your growth response but before you begin to detrain and lose it you hit that muscle again and do the same thing. The idea is that you can link up a series of these and grow in a linear pattern.
Pretty fucking cool eh? Too bad it's wrong. First, there's no scientific backing. Arthur Jones is partially responsible for this shit and he's long since recanted his short, intense, and infrequent methodology a la Mentzer's Heavy Duty. I will say that this program does work for beginners but for an experienced lifter it is drastically suboptimal. Oh yeah - if you take a shitty stimulus and magnify the response with enough drugs you can still make progress but for a given individual a supperior stimulus would allow for more gains at an individual's given dosage or equal gains for that person at a lower dosage level.
So where does that leave us? Well luckily people figured this stuff out a couple decades ago. There's a fatigue factor that gets built into this stuff and managing this fatique is important (both CNS and at the muscular level). You see, you can make gains and train without being fully recovered, it's actually better (think back to the people taking some time off and noticing they came back stronger - we'll revisit this in a moment). Rather than thinking about a single workout as a stimulus, consider a block of training - let's say 2-4 weeks. The fatigue is actually a recovery deficit that accrues during stimulative training. Unfortunately, a deficit means that it can't continue forever because you are running your body into the ground - but wait! This is actually fortunate.
You see, the idea that an experienced lifter can go into the gym and train once and then have his body respond with increased musculature on a consistent basis is rediculous. The body is first and foremost a survival machine. Muscle is calorically expensive and it's the last thing the body wants to add (people who had this genetic makeup died in famines very quickly and aren't around to reproduce). So a single session for an experienced lifter won't convince the body to pack on more muscle, and definitely not a short and infrequent stimulus because the body isn't convinced there is need. Bring in the fatigue accrual - in a training block of coninuously increasing fatigue the body gets a different message. The message is that there is a frequent, sustained, and increasing need for adaptation and that the body is falling behind and will soon break down under the strain. This is the stimulus we are looking for.
So now you train hard for 4 weeks and build up this deficit where you are right on the verge of overtraining (this point is called overreaching and the 4 weeks are called loading). The body knows it's screwed. What do you do? Pull the rug out and allow it to recover (deload). Generally you slash volume and frequency for a period to allow the body to recover and add some muscle in adaptation to the training stress. After a period of deloading you come back and load again - bigger and stronger (wait - remember about the BBers who took some time off and came back stronger - amazing fit is it not?).
This whole idea is called dual factor theory. Now most BBers haven't heard of it and couldn't explain it. It's largely greek to most of the people reading this. I mean, there are guys on here that know just about everything about drugs and diet but this is brand new to them. Well, it isn't brand new. It's not even remotely new or a little bit obscure. This is how 99.9% of the world's elite athletes are trained. We are talking near universal acceptance by every researcher and strength coach in the US, China, Europe, the Eastern Block, the former Soviet nations - everywhere. It's absolutely and totally prolific. On top of that there is a massive mound of scientific evidence to support it.
So how do you incorporate something like this? Logical question because in all my time at EF <I was here for a while as Madcow1 in 2000-2002ish too> I see people posting their programs and splits but there are critical factors missing. I can take the best split and exercise selection and bust my ass in the gym yet the stimulus is subpar because I'm not providing for loading/deloading. Generally this is handled by managing volume. A high volume period and then a low volume period.
There is a good program here that breaks many of the common rules in this thread (number of sets, frequency of training, all kinds of stuff). It has you squat 3x per week in addition to DLing once, rowing and benching twice. That won't work you say no one can squat 3x per week. Well it's actually not a problem and people have been running this program for 30 years and making huge gains. Several board members here are running it now or have just finished with big steroid like results but they were natural lifters (off the top of my head one is up 17lbs in week 7, another 16lbs in week 6, one younger guy was up 12 in week 6-7 but got that damn flu and has been out of commission). I didn't make this program so I can't take credit but it was orignally designed by Bill Starr, one of the greatest strength coaches ever, and later adapted by a Johnsmith182 from Meso who is actually one of the US' finest strength coaches - incidentally this job entails adding LBM to athletes in time constrained environments and this program is as good as any designed at doing it and far far better than just about anything most guys are using around here to add muscle. It's also avoided like the plague by weightclass constrained athletes who are near the top of their class as it simply causes too much weight gain and the diet restriction to prevent it is very severe. I ended up running it a few years ago and had to slash my calories twice in order to keep my gains down to the 8-10lbs range over 8 weeks (and I was not stuffing myself before). The cream of the program is that it is fantastic at adding LBM to an athlete but is also a very simple and easy to understand implementation of dual factor theory.
So anyway - that's the jist on training. None of this is revolutionary. It is in fact very standard stuff. The single factor camp is nearly empty devoid of anyone except BBers and I can certainly respect an educated choice to disagree in the face of all this but the fact that almost no one understands or has heard of what is the basic and dominant theory of training around the world doesn't exactly give me confidence that this is the situation. In fact the situation is that BBing has fallen so far behind on training knowledge that something really needs to be done.
I really hope this helps someone - I have no idea how training became all voodoo and the general population separated so far away ( likely A.Jones and Nautilus, the near extincation of Olympic Lifting, Weider's rosy image of BBing, the heavy reliance on steroids to compensate, who knows).