First let’s talk about balance and to steal a quote from Rippetoe “mean old Mr. Gravity”. If I were to drop a rock from shoulder height, where would it go? Straight down is the correct answer as it would take different force acting on the rock to get it to move in any other line. Why is this important? Well when we are under “load” aka the barbell it wants to move straight down. So it would make sense that we would need to balance this load effectively. Our center of mass or balance point is mid-foot. This means that when the bar is loaded on our “system” it needs to stay over mid-foot at all points in time. If the bar did not then this would be technically inefficient movement and therefore could be dangerous. However, when horizontal distance is created between joints and the barbell’s vector (position of bar straight down), levers will result in the spine/back, hips and knees. Below is a view of a properly balanced LBBS. We see the bar residing over mid-foot and the crest of the hips 1” below the top of the knee. Note the eye gaze…..DOWN!
To decipher the difference between the four squats we should discuss torque and moment arms. To create more torque or “stress” at a particular joint we would want a longer moment arm. This is the horizontal distance between the vector of the barbell (should be over mid foot) and the low back, hips and knees. This distance will create moment arms of varying force. Think of a rusty bolt and a wrench, would you want a short wrench or long wrench to break it loose? (long creates more torque) As you look at the picture below you will see a relatively long moment arm about the hips and low back in the LBBS and a relatively short moment arm about the hips and low back in the FS, and if we look at the middle (HBBS) we can see that this is somewhere in between the aforementioned. So we can take away that depending on where we place the bar, our torso and therefore knees will have to move in order to keep the bar over mid-foot, changing the various moment arms.
Now if we use our newfound knowledge of moment arms and torque we can decide which squat is the best. Simple question to ask yourself, which joint has more musculature, the hips or the knees? Hips of course. So it would make sense that we would want to have the longest possible moment arm about the hips. Therefore, the LBBS would be the way to go. You will be able to do the most weight and or most reps in this fashion. How about that squats are bad for your knees business earlier? I would suggest that the LBBS produces minimal stress on the knees as the moment arm about the knee is relatively short therefore reducing the amount of “torque” at the knee. Now if someone had a hard time maintaining bar position in the LBBS or they had a back issue that prevented them from keeping safe lumbar extension, I may then recommend the HBBS. I will still be able to load HBBS heavier than the FS due to the still larger moment arm at the hips. However, this lift will now be a little lighter than what I could have otherwise done in LBBS fashion. As a tertiary to the previous two squats I could implement FS. However, due to the increase moment arm about the knee and decreased moment arm at the hips the load will again decrease. Also, this movement takes a good amount of upper body and lower leg flexibility making it difficult to teach to most and with it being fairly “hard” on the knees I would advise to steer clear unless you are an Olympic lifter or someone who’s goal is to Clean a said weight. Lastly, we can discuss the OHS. This squat can be performed in any fashion you choose as a lifter. The only constant is that the bar must remain over….you guessed it….mid-foot! Most would choose to OHS in the fashion of a FS because it requires less chest flexibility, as the farther I lean my torso to the ground the more flexibility I demand of the chest/shoulders. However, this is all really a moot point because what is really the limiting factor of the OHS? Our leg strength will not give out first our shoulders will give out before our legs will. So I would say that it is a great tool for overhead stability and a necessity if you wish to Snatch, but if you wish to build leg strength resort to any of the previous three squats discussed.
We can deduce that the majority of trainees should be using the LBBS with some using the HBBS and very small fraction training the FS. In summary I will say this. “Squatting in any fashion is better than not squatting at all.” So find what works for you and what you can get comfortable with over time and make weekly gains on the bar. Train hard and train smart.