The name "abbreviated training" indicates that the training is low volume with limited movement selection. This name is something of a misnomer, for this style of training was en vogue from the late 1800s to about the 1960s-1970s. It was the method of greats like
and Paul Anderson
Once steroid use became more prominent, trainees could train for much higher volume sessions while still eliciting great gains, so training became higher volume with more movements, and thus anything not following this approach was deemed "abbreviated training".
You'll note then that abbreviated training was utilized and effective during an era where people did not have access to performance enhancing drugs (PEDs), and as such is still an effective choice for trainees who are training in a similar style. If you are making use of PEDs/chemical assistance, abbreviated training most likely is not the best choice for you.
The stuff they're using is a little more powerful than this
Why does abbreviated training work so well for a beginning, non-drug enhanced lifter? It operates under the premise that this type of lifter is primed to make rapid gains as a result of them being so new to training. The majority of "strength" gains that occur with a new lifter are simply the result of them becoming more proficient/efficient at the movement they are training. It is not unheard of for a new trainee to add 20-30lbs to their squat in 1 month, but this is not an indication that the trainee has gained the strength to move 20-30lbs more, but simply that they improved their coordination to the point that they were better able to recruit the muscles/motor units necessary to move more weight than before. This principle is critical to understanding why abbreviated training is advocated to beginners.
Whenever the topic of bulking is brought up, people love to quote stats about how much muscle someone can put on in a month, and why it's stupid to overeat. Numbers are thrown around from ranging anywhere from .25-1lbs a month being the max level a non-PED using trainee can put on. I don't know which study is the best, but in either capacity, using this same line of thought, it is unreasonable to expect a new trainee to be able to put on a great deal of muscle mass when they first begin training, especially if you get them to follow the supposed "hypertrophy routines" that are based around splitting muscle groups and high volume/low frequency. However, due to the fact that strength is gained by a new lifter more as a result of becoming a better lifter rather than a stronger lifter, it is not unreasonable to expect a new lifter to make great jumps in their lift numbers when they first start out. This is where abbreviated training is a boon, for the low volume of the training facilitates recovery for a trainee with a lacking work capacity, while the high frequency allows for many opportunities to make progress in the gym.
If you squat only once a week, you have 52 opportunities a year to progress in the squat. If you squat 3 times a week (like a lot of abbreviated training programs advocate), you now have 156 opportunities to progress within the same training period. This is 104 more opportunities to improve the mechanics of the squat for the sake of being able to lift heavier loads. Since you are in a period of rapid adaptation at this point, these multiple opportunities to excel mean much faster gains compared to a lower frequency approach.
One must understand that this is the point of these programs: to quickly reach peak levels of strength in a beginner trainee. By doing this, one has laid down a foundation of strength, coordination and (if you have been eating correctly) mass which can now be implemented toward a variety of training goals. Once this foundation is established, one can move toward bodybuilding, powerlifting, strongman, Olympic lifting, crossfit, etc. This is not a lifestyle, this is fleeting and ephemeral. Your goal should be to make the most of this phase and then move on to your real goal.
This is why when people say “these routines don’t make you look better” that it’s not a legit criticism. That is not their intent. Their goal is to get you to the point where you can finally start training to look better. The sad reality is that a sedentary lifestyle has become the norm, and most people enter lifting with almost no athletic background. These programs intend to make up for that by being a crash course in strength building so that one can actually start training.
You aren’t going to build an impressive physique with a 100lb bench. It’s just not going to happen. That is why putting a beginner on a high volume, high variety, low frequency program is a poor decision, as they simply will not be strong enough to lift heavy enough weights to make a meaningful impact.
So when is a good time to move on from abbreviated training? One of the best bench marks I’ve ever seen came from Stuart McRobert in “Brawn”, who advocated that a 5’9 man standing at 190lbs being able to bench 300lbs, squat 400lbs and deadlift 500lbs would be in a position to be able to start training with higher volume and more detail work (if their goal was bodybuilding). If the goal was powerlifting, this would be a great time to move on to something like Westside, Sheiko, 5/3/1, or a variety of other high volume programs.
If you find these numbers to be absurd, it is an indication that you need to be pushing yourself harder in your training. These are not the end of the road at all, but the beginning of a journey. A 1200lb total should not be daunting to a nearly 200lb man, but simply a stepping stone.
And in that same line of thought, one should not be married to abbreviated training, but instead realize what it is there for. Exploit it for all that you can, and move on. The zealots on either side of the training camp are equally annoying. Additionally, if you have completely stalled out on abbreviated training before hitting your goal numbers, and you cannot simply out eat or out sleep the stall (rare), try some higher volume training for a brief period to break past some plats. And even then, there are abbreviated higher volume programs, like 20 rep squats, which can be valuable both for mass and mental toughness building.