Torque is a trigger word in some circles of therapy and strength and conditioning. I think this mostly comes from a misunderstanding of what the word really means or what people may mean when they use it in certain instances. Here is the official definition of the word from www.dictionary.com. I am going to include the noun and verb versions of the word torque.
Mechanics. something that produces or tends to produce torsion or rotation; the moment of a force or system of forces tending to cause rotation
verb (used with object), torqued, torqu·ing.
Machinery. to apply torque to (a nut, bolt, etc.).
to cause to rotate or twist.
verb (used without object), torqued, torqu·ing.
to rotate or twist.
People like to get their panties in a wad over the word torque and the hips and squatting. Squatting has become so overly debated for no particular reason that there are now Universities dedicated to squats. I am going to discuss where I think this issue came from and how to understand what your hips need to do for different kinds of squats. If we are talking about the hips and squatting, torque means you are either twisting the hip joint internally or externally. If the hip is twisting internally, that means the knees are going to point in a bit and if you are twisting externally, the knees are going to point out a bit. Do not confuse this with having a valgus moment (knees come way inside the line of the big toe towards each other, typically without much control and it is really only an issue if we are seeing it on the descent) or a varus moment (knees being pushed way outside the line of the little toe). Neither of these is ideal for generating efficient power and both represent the idea of torquing the hip one way or the other to the extreme. We have really seen this with the idea of external torque of the hip and the squat where over the last several years people are over-correcting for this and over-cuing it as coaches. If someones knees are not diving in, they don't really need to be cued to drive their knees out.
The idea of external torque of the hip to squat has led me to fix a lot of inefficient squats over the years as I have been out teaching the MWOD Performance seminar (seminar schedule is linked). This is not to say external torque of the hip is not an important part of the squat, it is to say most people misinterpret the concept. They continuously drive their knees out hard as they descend, often times pushing their knees outside of their toes. This person will inevitably discuss having pain in the outside of the knee from the excessive varus moment under load and will always be chasing some mobilization that allows them to drive their knees out even further. They will also ask you how they can get their knees out further without feeling like they are only driving through the outside part of their feet. They are thinking about it all wrong. They have been over-correcting an problem they likely didn't have. They never were thinking about creating a strong and stable platform with their feet, setting their hips in the right position to descend with a little bit of external rotation, breathe in, brace hard, and just sit down. Dave Tate once said, "The most underused cue in squatting is squat." It took me a while to wrap my head around that, but the more I traveled and taught, the more I totally understood what he meant.
Enter the problem of taking advice about squatting for the masses from the leading experts in the field of equipped powerlifting. There is absolutely nothing wrong with equipped powerlifting. If you want to dedicate the time to slapping on a heavy duty squat suit and learning the technique of it, be my guest. The problem arises when we take the cues from that particular endeavor and try and make them work for a person that is not being caught by a triple ply canvas suit as they sit back with vertical (or even past vertical) shins and either stop at or ever so slightly below parallel (like you would have to have a laser to measure it). They are effectively creating power above parallel and for all intents and purposes are jumping, not really squatting. What this led to is many people trying to continuously drive their knees out further and further and try and keep their shins nearly vertical and go as deep as possible. This is fine if that is what you are training for and there are times in training to only use the part of the squat that takes you to parallel and back up. In fact, many coaches at high levels get chastised by internet experts for doing training blocks (or, gasp, all their squats) above parallel.
If you want to comfortably and efficiently squat below parallel (particularly if you are in the Ass to Grass for life crowd, an insufferable bunch), you are going to need a little different approach. You are going to have to rethink your squat a little. Not much, but enough to maybe do a thing or two you were maybe told was wrong. If you want to squat below parallel, you are going to need your femurs to be able to internally rotate a little. You also need your femurs to internally rotate while you are keeping a stable foot and ankle with even pressure of the foot on the ground between the first metatarsal head, fifth metatarsal head, and heel (again, things I go into great detail about at the MWOD Performance workshops).
This is where things get complicated (on the surface anyway). Most people correlate internal rotation of the femur with a valgus knee position. This can be true if a couple of other things are also true. If the person who is squatting has collapsed arches and ankles and their feet are turned out pretty far, this internal rotation of the femur as they get below parallel will likely cause a valgus knee moment, particularly on the ascent. I am not overly concerned with a slight valgus moment on the ascent of the squat. Typically it isn't even a valgus moment, it is just a correction of the femurs to a more midline position after the person has excessively externally rotated their femurs on the descent. If someone is going valgus on the descent, we have motor control and practicing of the squat pattern issues that need to be addressed before we go loading up to much.
Let's add to the fun with a little anatomy and muscle function. Let's take a look at the adductor magnus first. It is the largest of the muscles of your groin and its main function is to adduct the hip (bring it to midline). What is interesting is the part that attaches higher up your femur on the linea aspera, will externally rotate the hip, and the part that attaches farther down the femur on your medial epicondyle, will internally rotate the hip when it is being flexed and rotate externally. Process all of that for a moment. So as it is providing an internal rotation force to the femur as it flexes, it sets it up to extend the hip pretty powerfully out of the hole. I believe it may be responsible for up to 50% of the extension moment when your squat is deep.
Here is the deal, it isn't even that much of an internal rotation. If the person understands what is happening and how to set themselves up at the beginning of the squat to just allow themselves to squat, you probably won't even really notice it as an observer. It is really more of an internal rotation force that allows the femur to easily flex past ninety degrees so you can sink deeper into a squat. The feet stay stable and don't collapse, the ankle stays in line with the center of the foot, the knee stays over the ankle and foot (maybe some slight wobble from side to side, but the knee never goes inside the big toe or outside the little toe) and the hips stay pointed in the same direction as everything else. It is just what happens if a person can just squat and quit thinking so hard about it. Sure it takes some coaching up front to get the person to get out of their own head and just learn to trust their set up and get after it, but it is well worth it when they start to see they were making it way too hard on themselves.
So why is this important? There are even Olympic lifting coaches out there in other countries who have their lifters practice what is referred to as a hard controlled valgus maneuver out of the bottom of the squat to help generate force and use stretch reflexes to take advantage of the extension power of the adductor magnus and to set up the glute max to fire hard (by internally rotating the hip, the theory is you can get a stretch reflex of the glute and get it to kick in as you get to parallel) This is where you have to switch to external rotation to finish strong, just at or slightly above parallel, to drive the femurs back into external rotation to stand up powerfully. This also means the sticking point in the lift is going to be just around parallel as your body has to quickly transition between the two rotation moments. I personally don't coach the average person or athlete to do what the people at the highest levels of Olympic weightlifting are doing, but that doesn't make it right or wrong, you just have to understand the reasoning behind the decisions they are making during certain parts of the training cycle.
Here is a little video illustrating the subtle differences between allowing the body to naturally squat down and balancing the femur with a slight internal rotation force past parallel and excessively trying to externally rotate the femur the entire lift: https://vimeo.com/275713679/a53393b290
As I mentioned towards the end of the video, you can certainly do a squat where you force your knees out hard, but I would argue it is better suited for a wider stance with a lower bar position and when you aren't interested in getting below parallel (which may be a goal in your training cycle from time to time, it never hurts to squat a few different ways). What I want you to understand is if you are planning on squatting pretty deep and fairly upright with a higher bar position (which I think is more athletic and better for most people to learn up front, but we can differ on our opinions).
You may also hear someone talk about "pulling yourself into the squat with your hip flexors" which also can act as external rotators of the hip. The hip flexors are the iliopsoas, rectus femoris, tensor fasciae latae, and sartorius. I wouldn't call them powerful external rotators, but they do perform that function. This is where setting up correctly with stable feet and ankles and a nice braced trunk becomes so important. This allows you to just squat and let the forces around the femur act naturally to move between the slight external rotation during the set up and initial descent and the slight internal rotation as you move below parallel before you reverse and move back towards external rotation to finish. All this time the feet, ankles, knees, and hips stay stacked and you may not even notice all of this is going on. I am even hesitant to use the word rotation as if we could run an x-ray while we are squatting, we may not even see much of a change. Here are a couple of pictures to illustrate my point. The first one is me just letting myself naturally squat down after I get my feet set where I want them. The second picture is me excessively externally rotating my femurs, driving my knees beyond my little toes. Notice that both positions have a stable foot and ankle. Also notice which one is deeper. I can squat well over 400lbs either way, the first way just feels more natural and I don't have to think. If I squat heavy as in the second picture, it feels more forced.
This is why my go to when teaching a new person to squat is the sandbag squat. Holding a sandbag in the bear hug pretty much forces the person to squat correctly without much coaching. It teaches them to brace and breathe with some feedback from the bag, and it helps them learn to stay as upright as their body will allow. I have taken some pretty interesting squats from people that were thinking way too hard about squatting and had them moving much better in a matter of minutes. People really just need to uncover their natural ability to squat in the way that is best for their body shape. As a coach, you have to help people with certain principles and parameters up front, but then you need to get out of their way and let them learn. You can always make adjustments here and there as you go and layer on more complex ideas around setting up and breathing and bracing. You can get more technical about what is happening at what joint or muscle in the future if the person even cares to hear about that stuff.
I am well aware that their are people with different femur lengths and hip sockets and whatever other dumb argument people want to have with me. In the grand scheme of things, a lot of that stuff doesn't matter that much if a person squats in a principled way. Feet stable and arched up (to all you flat foot apologists out there, I haven't done a seminar yet where I couldn't get someone to stabilize their "flat feet"), ankles in line, knees in line, hips in line, trunk solid and braced, don't collapse anything and go as deep as you can. This may mean you are above parallel for a while and don't have to worry to much about the other part. What I will say, is you will find it will likely become difficult to ever squat deeper if you keep chasing more and more external rotation and never learn to just squat.