All the complicated science, Selye's General Adaptation Syndrome, super compensation curves, etc. point to one simple fact: unless you are doing more, you won't get bigger. If you only ever spend 15 minutes at a time under the sun, you are only going to get so tan.
It would be better to restate the question like this:
How can I can I increase size without killing myself in the process?
To answer your original question, yes you can get bigger without going to failure all the time. In fact, that's how you stay at it longer and avoid injury. The important concept to understand is progressive overload. As Kirk Karwoski puts it: "if you put more weight on the bar, you're stronger".
Rating of Perceived Exertion
Runners have been using this indicator for years to help their training. Mike Tuchscherer (a power lifter) came up with a way to apply it to weight lifting. If we were to reinterpret his RPE scale for body builders it would look something like this:
10) Set to failure.
9) Last rep is tough, but still 1 left in tank
8) Too heavy to go fast, but not a struggle; still have 2-4 reps left in tank
7) Can use maximal force to move bar quickly
6) Can use moderate force to move bar quickly
4) Rehab work: 20+ rep sets designed to get blood moving
1-3) not worth worrying about (i.e. life)
If I understand you correctly, you want to live in the RPE 8 world, and increase the weight used for that over time.
Progressive Overload Without Maximal Work
You will need to alternate your target RPE from 7-9. For example, over a month you would do something like this:
- Week 1: RPE 8
- Week 2: RPE 8
- Week 3: RPE 9
- Week 4: RPE 7
The way you break up the sets/reps is up to you. If you want 3x10, 3x12, 5x8, etc. at the end of all the work it should feel like the RPE rating above. One strategy to help ensure you hit that if you under-estimate the weight you need is to turn the last set into an AMRAP set. In other words, As Many Reps As Possible to hit your target RPE.
If the weight you used this time was too low to hit your RPE target spot on, then increase it next time. The purpose of hitting RPE 9 at least once a month is to force your body to adapt to something heavier. Following it by a week at RPE 7 helps your recovery, so you can spend most of your time at RPE 8.
A good strategy is to use much heavier weights and shorter sets for RPE 9 work. Let's say you can bench 225 3x10 with an RPE of 8. You might decide to do 250 3x3. The next time you get to RPE 9 work, you'll want to increase the weight, even if it's just 5lbs. It should be possible for a while.
Yes, not pushing yourself to physical exhaustion and failure is a good thing. Failure takes a lot more out of you than it's worth. As long as you keep increasing your work load over time (progressive overload), you will get bigger/stronger. Changing rep ranges also helps toward the goal of getting your body ready for heavier weight.