Squatting and repetitive movement injury

As of late, the multi rep sets I've been doing in the squat exercise has caused my lower spine to become tender and somewhat painful. To remedy this, I've stopped doing multi rep sets and instead I've been doing single rep sets.

This has diminished my pain significantly.  The fact that I was breathing with a large load on the back of my neck was compressing my lower back which is somewhat painful. Also with each breath I was also losing that tight straight up and down form so crucial to avoiding putting the spine in a compromised position susceptible to injury.

But the problem with doing just single rep max out sets is that it's harder to achieve necessary fatigue that will induce an adaptive response strength gain. That cliche "no pain no gain" rings true when strength training and I can pretty much guarantee you will no see no strength gains if you don't experience any soreness in your muscles after you workout. To remedy this, I've taken to doing five or six max out single rep sets instead of just the  four max out sets. It's true I do experience soreness in my glutes and quadriceps without doing multi rep sets but the degree of soreness is somewhat diminished and seems like my squatting range of motion is not as fluid as with doing multi rep sets.

As far as making any strength gains, I have made some but I really haven't done enough single rep sets to give conclusive evidence that just doing  single rep sets will elicit a proper strength gain adaptive response. My guess is that it will but since the degree of fluidity is lessened when just doing single rep sets the strength gains will be smaller.  Who knows maybe I'll go back to doing multi rep sets. I guess I could also do single rep sets with lighter weights to increase the speed in the range of motion and this will help with my lifting efficiency.