My preference has always been to do 3 sets of 15 reps, for whatever exercise (bodyweight or weights) that I can. My opinion is that being consistent with strength is more important, and if I can't reach that level, there's no durability in my strength. From a personal look-level, it also results in not having 'bloated muscles'. It does result in increasing the strength over time, and I've found my max 1-3 rep has increased when I do it as well, but the dividends aren't particularly noticable to people. What are your thoughts on this on a functional level?
I'll start by addressing the 'bloated muscles', physical appearance, part.
There's a lot of conflicting lore out there when it comes to how strength training impacts appearance. If you go on body building forums, for instance, a lot of people will tell you that they don't do HIT because it just increases strength and it can't make you big. If you go on forums devoted to competitive strength related activities, you'll get people who tell you they don't do HIT because it's only useful for bodybuilding and you can't get strong from it. So, it's not surprising that this topic generates a lot of confusion.
Last I looked at the research, and my own experience agrees, if someone performs strength training that is sufficient to stimulate an adaptive response, the body is going to respond according to its own genetic programming, regardless of the strength training protocol employed. So, if you work hard enough that your body actually adapts to get stronger, whether you lift light weights for a lot of reps and sets, or you lift heavy weights for a very few reps and sets, or something in between, your body is going to build size and shape in the same way. It may happen faster or slower, depending on the quality of the exercise, but in broad terms, if you want to be X strong, you're going to have to be Y big, based on your genetics. It's probably not quite that simple if we're trying to be super precise, there's probably a little wiggle room to shift things a tiny bit one way or the other, but for all practical purposes it's probably a waste of time and effort to try to emphasize one aspect or the other.
For a given individual, and barring things like injury, a bigger muscle is a stronger muscle. Strength gains always precede size gains and, for pretty much all practical purposes, the body adapts by first increasing muscular strength until that becomes inefficient, and then it increases in size, at which point it will increase in strength again until it has gotten all the gains it can out of that size increase, wash, rinse, repeat. Sure, there are little guys that are stronger than big guys, but if you had an identical twin the one of you with the larger muscles would almost certainly be the stronger, regardless of how you each trained.
The last thing I'll say about appearance is that for most people, men and women, it's actually pretty hard to get big without the use of PED's and it's impossible to get
really big without a solid combination of the right genetics and PED's. I've been a devoted lifter for decades and I've used both high-ish volume, low-ish weight protocols and very low volume, very high weight protocols and I don't look anything like a bodybuilder and never have. In over a decade of owning a gym and close to 2 in the industry, I've had only 2 clients get kind of bodybuilder looking and both of them were fairly muscular even when completely untrained.
It's important to note that I said "kind of bodybuilder looking". They were not big by the standards of competitive "natural" bodybuilding and absolutely tiny in comparison to the IFBB pro's. I put quotes around natural because it's important to understand that some good portion of that community is just more discrete about their PED use. There's also a surprising amount of PED use in the general populace and it's rampant with fitness influencers.
Now, talking more directly about strength considerations, as long as you're doing something that provides a sufficient stimulus to trigger an adaptive response you'll get stronger. So, 3 sets of 15 reps will do the job as long as the resistance you use represents a sufficient stimulus to trigger an adaptive response and as long as you increase that resistance over time so that it always represents a sufficient stimulus for your stronger muscles. In general, all other things being equal, you'll get faster results with your 3x15 workouts the heavier the weight used, so long as you get sufficient rest, nutrition, and time to allow your body to adapt after each workout.
It's a little tough to give much more feedback, because I don't know all the variables. How fast are you moving the weights, how close to failure are you at the end of each set? If you're using a 2/2 protocol for instance, where you lift the weights in 2 seconds and lower them in 2 seconds, then 15 reps is ~ 60 seconds. If you're at, or very close, to failure at the end of each set in that time frame you're probably providing a great stimulus to generate both strength and bone density improvements and probably a pretty good stimulus even if you aren't close to failure until your last set. If you're using a 1/2 protocol and you're nowhere near failure at any point you may not be providing a very strong stimulus for strength nor bone density improvements. If you're using a 6/6 protocol and you're going to failure you're probably going to get a pretty good to great stimulus for strength improvements but you may not be doing as much for your bone density. Etc.
My opinion is that being consistent with strength is more important, and if I can't reach that level, there's no durability in my strength.
I'd love to address this point, but I'm not clear on what you mean by "durability" in this context. Do you mean endurance, time before your progress begins to regress, or recovery or something else?
Final thoughts:
I've talked about bone density, but bone density is something that I'm not sure we've got a real handle on yet. The research I've seen tends to indicate that you need to lift pretty close to your 1RM to provide a strong stimulus for this purpose, but research also tends to indicate that you can increase your strength with high volume, low weight exercise, as long as you inroad the muscles sufficiently. My understanding and experience has been that stimuli that cause muscular adaptation tend to cause adaptation in associated tissues, so I find it a little surprising that strength increases can be strongly stimulated without stimulating corresponding density increases in the related bones. I'm not sure what I'm missing or misunderstanding or if the current research is missing something, or what. So, overall, I'm saying don't take anything I've said about bone density as super concrete.
There's more that we could talk about, in terms of the value of big compound movements as opposed to small rotary movements, and on and on, but I worry that I've already written more than anyone wants to read and don't want to come off as pedantic. I am tired and I wrote this without proof reading before bed so hopefully it's not too disjointed!
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