TL;DR version: Do you need to “bottom out” in the squat in order to receive the benefits of the stretch-reflex/bounce? If that position seems to bother a chronic pain issue, but I can still get to below parallel, should I even bother with trying to expose myself to the rock-bottom position gradually, in order to be able to train my squats to that depth?
General context and considerations:
In Knuckols’ “How to Squat: The Definitive Guide,” he talks about a benefit to bottoming out the squat in order to use the stretch reflex. I think I’ve seen similar thoughts from the Juggernaut crew, and most weightlifting coaches seem to believe so as well. (I do see more of a benefit to weightlifters training the bounce in the front squat, at least, since they’re generally catching the bar in, or very near, their rock-bottom position.)
Even though the idea seems to pass the sniff test, when I’ve thought about it more, considering real-world applications, I’m not even close to confident about it. (Maybe, mechanistically, the stretch reflex is stronger the further the muscle spindle is stretched.) My first real-world counterexample would be: people who squat high. When people squat higher, they seem to squat more weight. It looks like this holds true whether the difference is between above parallel and parallel, parallel and to competition depth, or competition depth and ass-to-grass. Also, when I think about RDLs and stiff-legged deadlifts, I feel like I’d have to be crazy to say that going to end-range would, necessarily, allow someone to lift more weight. Otherwise, we’d all be doing our SLDLs from a 6-inch deficit. Overhead pressing seems to be easier (at least for multiple-rep sets without a pause) if the range of motion is cut. Jumping still benefit from a countermovement, even though there is no "bottoming out,’ same thing with a bunch of other sporting movements I can think of.
I think I’m at the point of thinking that: if someone can do it, and it doesn’t negatively affect their training, there is probably some benefit. However, the difference between “hip crease below the top of the knee” and “ass-to-grass” is probably not worth considering for anyone other than Olympic Weightlifters (and maybe some full-rom bodybuilding zealots) .
Personal considerations:
In my specific case, bottoming out in the squat seems like it might not be the best idea. My hips, especially my left one, have been bothering me off and on for a long time now. When I was doing Phase I of the Bodybuilding I template, I did feet-forward smith squats because I hate my gym’s leg press machines. I noticed that my hip was a bit less pissed off when I didn’t completely bottom out the movement, and there wasn’t a decrease in performance. So, I still went below parallel, but I didn’t go ass-to-calves.
I’m probably going to experiment with doing the same thing with my other squat movements, essentially cutting my depth to above my natural rock-bottom but below competition depth. Whether or not I’ll be losing the stretch-reflex, or even part of it, I know it’s a good idea in the long run if I end up with less of my chronic hip pain and can train harder, more consistently. But, I am curious if I’ll be missing out on anything and might benefit from experimenting with more exposure to that position with the goal of being able to bottom out my squat at my normal speed later on.