Frequency is King for adding both Strength & Size.
There are a few people who can indeed bend or completely shatter this rule, they are as follows:
– PED users.
– Genetic Elite (however frequency gives them more oomph).
– The Strong.
Now when it comes to PED users they will have an increased rate of recovery, protein synthesis and generally be more anabolic. The same is true for the genetic elite, while they are natural, their body responds far better which means they can make great progress on minimal frequency.
Both PED users and the Genetic Elite do benefit from training at a higher frequency, you can look back at various training records across differing sports to confirm this, there are several references in the Science & Practice of Strength training and Super Training if you want a place to start.
So what about The Strong?
What is strong?
Is a 405lbs or 180kg squat strong? Yes, but it’s not earth shattering. You could still get a benefit out of squatting 2-3times per week with sub max loads based on those squatting numbers. However if you are squatting 700lbs or 317kg you might do well squatting once per week or maybe even less frequently because of the amount of neurological stress handling even sub max weight would induce.
Now strength is indeed relative, to a point. A 60kg lifter lifting 180kg may adhere to the rule of less frequency, they may not.
The bottom line is that being strong may require you to use a lower frequency, until that weight becomes light, then you increase frequency to once again progress until you start hitting ridiculous numbers, but once you start hitting those you can do pretty much what ever you like.
Unless you are one of these incredibly strong individuals erring on the side of more frequency of a lift (2-4 times per week on separate days or more with twice or triple day training if you have the luxury) will get you better results than hitting it just once.