Stick with me here, I'm going somewhere with this
This seems obvious, but many times I have fallen into the trap of concerning myself with the growth of the assistance work itself, rather than its benefit to the primary lift. If I was interested in improving my competition squat for powerlifting, I may pick squats as assistance work as well. If I was squatting 5x10 after working up to a heavy single, I would monitor and track the weight progression of my assistance work. If I “stalled” on my assistance work squats, I would start coming up with ways to break this “plateau”, and suddenly I was now basing my programming around making my assistance work increase, rather than actually focusing on the entire purpose of the program: to make my competition squat better.
You’ll note that I put the words “stall” and “plateau” in quotes in the above. The reason is simple: these can’t actually happen with assistance work. Not if you are employing it correctly. With the entire point of assistance work being to assist a primary lift, it does not matter what direction the assistance work progression is going, only its impact on the primary lift. If your assistance work weight is steadily increasing while your primary lift stalls or regresses, your assistance work is failing to perform its mission. If, however, your assistance work is not increasing in weight, or even regressing, while your primary lift increases, your assistance work is working, and nothing should be changed.
The primary variable playing into assistance work stupidity is not having a clearly defined and accepted goal. In terms of the former, it requires a final destination in mind before starting on the journey. Are we here to create a bigger squat, bigger muscles, faster run time, whatever. If nothing is concrete, we have no way to know if our assistance work is working, because it is assisting nothing. It simply exists.
It does you no good to make the journey convenient if you end up going nowhere
In terms of the latter, it requires there to be some actual honesty with oneself in regards to the goal. Do we really want a bigger squat, or is that just something we tell ourselves when really it’s all about having a bulging upper body? Did we buy into the internet’s claim that the upper body is built by the squat, or are we too afraid to admit to being a little vain? Not being honest with oneself means we won’t notice when we try to sneak stuff into the assistance work. We may know that, to squat more, we have to perform the squat more frequently, but we also know that whenever we front squat it gives us a really sweet looking teardrop on the quad, and hey, maybe it’ll also make the squat go up.
"It really makes my deadlift go up, I swear!"
We like to believe that assistance work is scientific and specific and predictable and logical, but sometimes there is some sorcery at play. Referencing my concept of “accidental strength” (which I have written a post on before if you which to search for it), it can sometimes be the case that we have weaknesses that we’ve never even thought to diagnose due to never putting ourselves into a position wherein they can be tested. Assistance work that we can kick ass on ends up with our gains on the primary lift regressing, whereas performing assistance work we are terrible at may end up giving up tremendous gains, even with paltry weight and goofy technique.
It is because of this somewhat magical nature of assistance work that I find less thought to be of greater benefit than more thought. Many times, in my own training, I will simply pick A movement to train for assistance work and hammer it hard after my primary lift. If my primary lift keeps increasing, I will keep performing the assistance work. If it does not, I will dump it. Eventually, I may gather something of a “greatest hits” list of assistance work that I regularly cycle for one lift, but what is peculiar is that I rarely break previous “records” with these assistance lifts. Looking through my training log, whenever I squat for assistance work, I regularly start my cycle at around 275lbs for 3-5 sets of 10, and tend to end up stopping at around 335. I have done this for years, yet my squat single has continued to steadily increase, despite being in a “rut” for the assistance work. It simply necessitates that I do not get hung up chasing numbers and records on the lifts that do not matter, and keep myself focused on what is actually important in my training.
The bottom line is this: assistance work is only as valuable as its ability to make your primary lift stronger. Don’t train to be better at assisting, train to dominate.