A few weeks ago I was having a conversation with one of our interns at Boost Physical Therapy & Sport Performance on the topic of squat mechanics. His question is one that I hear all the time, “Do front squats train the quads more than the back squat?” I looked at him dead in the face and said “no.”
Now most of you may be thinking in your head, “Aaron what are you talking about? Everyone knows front squats are more ‘quad dominant’ than back squats and therefore work the quads more!” However, before you completely dismiss my answer, let me explain the why behind my response.
A year ago I wrote a blog article entitled “The Real Science of the Squat” where I broke down the biomechanics of the different squat techniques. In the article I explained how torque is generated and manipulated at the hip, knee and low back through the use of a static mathematical model.1,2
Here’s a quick summary.
The Real Science of the Squat
Imagine you’re holding a 10 lb dumbbell in front of yourself at shoulder height. Do you feel the weight of the dumbbell trying to pull your arm down? What you’re feeling is the force of gravity. It always pulls straight down. As gravity pulls down on the dumbbell, it causes a rotational force at the shoulder joint. This force is called torque. The muscles of the shoulder must then be activated to overcome this force in order to hold the weight from moving.
The distance from the force of gravity and the point of rotation (your shoulder joint in this case) is called a lever arm. Much like a wrench turning a bolt, the longer the lever arm the more rotational force (torque) can be applied at the joint.
Imagine now someone tied a rope around the same 10 lb. dumbbell and attached it to your elbow. It would now be much easier to hold your arm in front of you. This is because the length of the lever arm decreased, which meant there was less force (torque) required by the shoulder to keep the arm extended. Make sense?
But how does this relate to the squat?
If we take a snapshot of a squat at its parallel position, we can calculate the amount of torque that is generated at each joint complex (hips, knees and low back). Like we mentioned earlier, gravity always pulls straight down and during the squat it is often represented as a vertical line drawn through the middle of the barbell. This vertical line then runs through the body and divides the thigh.
The distance from this vertical line to the center of a joint becomes a lever (just like a wrench turning the bolt). Often sport scientists will analyze the squat at a parallel squat position (hip crease in line with the knee).1,4 The longer the lever arm in this position, the more torque that will be generated at that joint during the squat.
The Torque Differences Between Front & Back Squats
When we analyze the different squat techniques, we find a few interesting things.
- The back squat has a longer lever arm compared to the front squat, making it more efficient for lifting big weight (this is known as leverage). Mechanically, our bodies can squat more weight when the lever arm is longest at the hips.5
- The front squat (with the more upright trunk position) creates a longer lever arm at the knee and therefore places more torque on the knee joint.
Many will take these findings and claim the back squat is therefore more “hip dominant” compared to the “quad dominant” front squat. They will also think that because there is more torque placed on the hips or knees in a certain squat technique, the musculature that surrounds that specific joint must work harder to overcome that force.
Unfortunately, that’s not how the body works during multi-joint movements like the squat. Let me explain.
Forget What You Learned in Anatomy 101
A lot of the misunderstanding on this topic comes from the way we learned about the body in the first place…our anatomy textbooks. Think about how muscles and their function are described in school. You have muscles that cross only one joint (called mono-articular) and muscles that cross two joints (called bi-articular).
In the front of your thigh for example, you have the vastus medialis and vastus lateralis. Both muscles cross only the knee joint and are therefore considered to be mono-articular muscles that extend the knee when they contract. The rectus femoris is another quad muscle that helps with knee extension. However because it also crosses the hip joint (making it a bi-articulate muscle) it is capable of flexing the hip joint as well when it contracts.
On the opposite side of the thigh we find the hamstrings and glute max. The glute max is one of the most powerful muscles of the entire body. It is a mono-articulate muscle as it only crosses the hip joint. The semitendinosis (one of your hamstrings) is a bi-articulate muscle as it crosses both the hip and the knee joints. This muscle can therefore be used to extend the hip or flex the knee, making it a direct antagonist of the quads. According to your anatomy textbook, if the quads are contracting hard to try and extend the knee the hamstrings have to relax to allow the movement to occur. Sound familiar?
This is where things get interesting.
In the early 1900’s there was a biomechanist named W.P. Lombard that looked into how the body really works, outside of our textbook understanding. The “paradox” he described occurs when muscles that should technically oppose each other are both active during certain movements. For example, when we perform a squat, the hamstrings and the quads are both activated.
If the hamstrings (which flex the knee) are activated at the same time as the quads (which extend the knee), shouldn’t the body just freeze up and not move? According to how you learned about muscles in school, this doesn’t make sense.
Our body uses bi-articulate muscles (like the hamstrings) to transport energy from one joint to another. Many experts in the field of biomechanics stress that when a bi-articulate muscle is activated during a motion like the squat, movement at one joint instantly creates an opposite reaction at the other joint in which the muscle spans.22
For example, when the glute max (a mono-articulate muscle) contracts to extend the hip during the squat, the rectus femoris (a bi-articulate muscle) on the other side of the leg is activated as well to aid knee extension.
When you stand up from the bottom of the squat, the hips and knees extend at the same time. During this process the bi-articulate muscles of the hamstrings and rectus femoris are activated BUT do not change in length. The hamstrings are shortening at the hip joint and lengthening at the knee joint while the rectus femoris is lengthening at the hip joint and shortening at the knee joint.
For this reason, bi-articulate muscles have been regarded as “tendons” as they allow mono-articulate muscles to have an indirect action on a joint they do not pass. This means the activation of the hamstrings and rectus femoris do NOT cancel each other out and lead to cramping or freezing of movement!
We can therefore come to the conclusion that during the squat:
- The glutes can indirectly extend the knee joint
- The quads can indirectly extend the hip joint
Basically, the glutes and vastus muscles of the quads function as force and work generators while the hamstring and rectus muscles distribute torque and power between the two joints.
Did I lose you yet?
We can now use this understanding to help answer the question “are the quads activated more during a front squat than a back squat?”
While there is clearly more torque comparatively placed on the knee joint during a front squat, the body does NOT activate the quads more to overcome this force. The quads are already “turned on” during the squat in order to lift the weight. Instead the body redistributes power from the hips to the knees to help the body complete the lift.
Therefore the quads are not activated more in a front squat than a back squat.
What does the research say?
There is a multitude of studies that have compared the front and back squat and found no significant differences between the lifts in terms of muscular activation.
Recently in 2016, a group of researchers led by Dr. Jonathan Sinclair compared the front and back squat at the same weight (70% of the 1 RM front squat). While there was more forward lean seen in the back squat (qualifying it as a more “hip dominant” lift) they found no significant difference in muscle forces in the lower body.13
Other experts in the field of sport science Dr. Bret Contreras and Dr. Brad Schoenfeld, had a group of 13 women with experience in resistance training perform their estimated 10-rep maximum in the front squat along with the back squat to parallel and full depth. They found no significant difference between any of the lifts and variations.12
In fact, only 1 scientific study to our knowledge has ever shown any difference between the two lifts in terms of muscular activation. The researchers found the vastus medialis was activated to a greater degree during the front squat while the semitendinosis was activated more during the back squat.23 These differences however did not appear until maximal weights in each lift were attempted and they also found no significant difference in any other muscles between the two lifts (including the other vastus muscle or hamstring muscles).
Busting Through a Sticking Point
In a recent article Greg Nuckols (an experienced coach, author and powerlifter) explained how this concept can help us learn to grind through a sticking point of a squat.6 When most athletes miss a squat, they end up getting stuck about half way up (when the hips are above parallel). By applying what we learned today, we can conclude the lift stops ascending because the body is unable to create enough force to overcome the torque created at the hips (which are still left in a flexed position).
Greg theorized that by driving your upper back into the bar and pushing your knees forward (shifting your hips under the bar) you can effectively grind through a sticking point. This movement decreases the length of the lever arm length at the hip joint and therefore the amount of torque the hips need to overcome. This means less force is needed at the hips to overcome the torque, leading to an easier ability to stand up and finish the lift!
Understanding The “Good Morning” Squat
We can also use our new understanding of Lombard’s paradox to explain one of the most common technique faults, the “good morning squat” or “stripper squat”. This describes the problem of the hips rising faster than the chest on the ascent of the lift.
There are 2 main theories as to why this problem exists.
- Quad Weakness
- Coordination Problems due to Fatigue
Many are under the impression that quad weakness is the main culprit behind this technique flaw. However, when you look at the research, there are a number of flaws to this idea. First, the majority of research to support this theory centers on studies performed on subjects lifting boxes or sandbags from the ground (not a barbell on their back).
In 2012 a group of researchers from Cairo University analyzed the technique and muscular activation of a group of participants while lifting a sand bag weighing roughly 30% of their bodyweight. After fatiguing their quad muscles in isolation (using an expensive isokinetic machine) they reanalyzed their movement pattern and found they tended to lift more with their back!20 A number of similar studies have found these same results.19,21
However, what these studies failed to demonstrate is how the body responds to fatigue when lifting a weight on the back. This means their results cannot be generalized to a movement like barbell squatting. The movement of picking up a box from the floor is different than when squatting a barbell on the back.
This is where the second theory comes into play.
During the ascent of a squat we ideally want the chest and hips to rise at the same. This keeps the bar centered over the mid-foot, which means the body is in balance and capable of producing efficient power.
However as athletes fatigue while squatting (near the end of a high rep training session or when attempting a near maximum weight), they often lose their ability to stay balanced and maintain perfect coordination, allowing their chest to fall forward.14,16,17 Excessive forward trunk lean leads to the hips rising faster than the chest on the ascent of the squat, which lengthens the hamstrings. Because the bi-articulate hamstrings are now lengthened, the body loses the ability to transfer force from the quads to aid the glutes in hip extension.
Dr. Gregory Myer and Dr. Brad Schoenfeld have explained this fault as a problem with suboptimal motor recruitment patterns (i.e. the ability for the body to turn on the right muscles at the right time to maintain technique).18
What this means is the “stripper squat” isn’t caused solely by a lack quad strength but rather due to problems in coordination and motor control that leads to a disruption in “lombards paradox”.
I find that instead quad weakness, the more likely cause of this technique fault is the ability to “turn on” the glutes at the right time due to fatigue.
In a recent study, researchers looked at the muscular recruitment changes the body takes when lifting near maximum and maximal weights. They found that when experienced athletes jump from 90% to 100% of their 1RM, they actually recruit their glutes more in an effort to keep their chest upright on the ascent.17 The researchers commented that this action transfers force from the hips to the knees, allowing the body to complete the squat ascent with the more ideal upright chest position.
If the athlete has pushed into such a fatigued state that it has effected their coordination and allowed their hips to rise too quickly, have them drop the weight and perform their remaining sets at a weight they can show better technique.
So the title of today’s article is really a trick question. The real answer is neither! While a squat may look more “hip dominant” or “quad dominant” the squat does not exclusively train the quads, hamstrings or glutes. All of the muscles of the lower body are activated together to extend the hips and knees regardless of how the squat looks or the amount of torque that is placed on the joints.
If there is less torque on one joint, the body redistributes energy from the vastus quad muscles and glutes via the hamstrings and rectus muscles to help overcome the increased torque at the other joint.7
I once heard someone say, “Nature never works against herself.” I hope that this article was able to help you take a step back from the traditional textbook way of look at the body and expand your understanding for how movement really happens.
Until next time,
*A special thank you to Greg Nuckols and his writing for being an inspiration for this article.
1) Rippetoe, M. (2011). Starting Strength. Basic barell Training. 3rd The Aasgaard Company. Wichita Falls, Texas.
2) Fry AC, Smith JC & Schilling BK. Effect of knee position on hip and knee torques during the barbell squat. JSCR. 2003. 17(4):629-633.
3) Diggin D, O’Regan C, Whelan N, Daly S et al. A biomechanical analysis of front versus back squat: injury implications. Protuguese Journal of Sport Sciences. 11(Suppl. 2), 2011; 643-646
4) Wretenberg P, Feng Y, Arborelius UP. High – and low-bar squatting techniques during weight-training. Medicine & Science in Sports & Exercise. February 1996; 28(2):218-24
5) O’Shea P. The parallel squat. Natl. Strength Condit. Assoc. J. 1985; 7:4-6
6) Nuckols, G. Squats are not hip dominant or knee dominant. Some biomechanical black magjic. Web blog post. Strongerbyscience.com. 14 Oct 2015. Web 29 Jul 2017.
7) Multiple Muscle Systems: Biomechanics and Movement Organization. J.M. Winters and S.L-Y. Woo (eds.). 1990 Springer-Verlag, New York.
8) Cavanagh PR & LaFortune M. Knee flexor moments during propulsion in cycling – a creative solution to lombard’s paradox. J. Biomechanis. 1985; 18(5): 307-316
9) Yavus HU, Erdag D, Amca AM, Aritan S. Kinematic and EMG activities during front and back squat variations in maximum loads. J Sports Sci. 2015;33(10):1058-1066
10) Gullett JC, Tillman MD, Gutierrez GM, Chow JW. A biomechanical comparison of back and front squats in healthy trained individuals. J Strength Cond Res. 2008;23(1):284-292
11) Russell PJ, Phillips SJ. A preliminary comparison of front and back squat exercises. Research quarterly for exercise and sport. 1989;60(3):201-208
12) Contreras B, Vigotsky AD, Schoenfeld BJ, et al. A comparison of gluteus maximus, biceps femrois, and vastus lateralis EMG amplitude in the parallel, full, and front squat variations in resistance trained females. Journal of Applied Biomechanics. 2015.
13) Sinclair J, Atkins S, Vincent H, et al. Modelling muscle force distributions during the front and back squat in trained lifters. Central European Journal of Sport Sciences and Medicine. 2016; 14(2):13-20
14) Hooper DR, Szivak TK, Comstock BA, et al. Effects of fatigue from resistance training on barbell back squat biomechanics. JSCR. April 2014; 28(4):1127-1134
15) Van Dieen J, Toussaint HM, Maurice C, et al. Fatigue-related changes in the coordination of lifting and their effect on the low back load. Journal of Motor Behavior. 1997; 28(4):304-14
16) Sparto PJ, Parnianpour M, Reinsel TE, et al. The effect of fatigue on multijoint kinematics, coordination, and postural stability during a repetitive lifting test. JOSPT. 1997; 25(1):3-12
17) Yavuz HU, Erdag D. Kinematic and electromyographic activity changes during back squat with submaximal and maximal loading. Applied Bionics and Biomechanics. 2017; Volume 2017:1-8
18) Myer GD, Kushner AM, Brent JL, et al. The back squat: a proposed assessment of functional deficits and technical factors that limit performance. Journal of Strength and Conditioning. 2014;36(6):4-27
19) Trafimow JH, Schipplein OD, Navak GJ, et al. The effects of quadriceps fatigue on the technique of lifting. Spine (Phila PA 1976). 1993;18:364-367
20) Adel SM, Battecha KH, Abo ElAzm SN. The effect of quadriceps fatigue on back muscles electromyographic activity during lifting in osteoarthritis patients. Bull Fac Ph Th Cairo Univ. 2012;(17)2:55-63
21) Makoto S, Akira H, Massahiko W. Influence of quadriceps femoris fatigue on low back load during lifting of loads at differet distances from the toes. J Phys Ther Sci. 2008;20:81-89
22) Van Igen Schenau GJ, Bobbert MF, Rozendal RH. The unique action of bi-articular muscles in complex movements. J Anat. 1987; 155:1-5
23) Yavus HU, Erdag D, Amca AM et al. Kinematic and emg activites during front and back squat variations in maximum loads. Journal of Sport Sciences. 2015;33(10):1058-1066
30 thoughts on “Is Your Squat “Quad Dominant” Or “Hip Dominant?””
Dr. Horschig and Dr. Sonthana,
Thank you for writing this article. I appreciate the homework you gentlemen did to answer such a great question. I found the explanation of when/how/why the recruitment of the anterior and posterior chains occurs to be useful and easy to understand.
Could you speak more to the torque one must create at the joints during the squat, to include the thoracic and lumbar spine, the hip, and the knee, please? Specifically, internal vs. external torque and in which phases?
Does the torque one creates at the midsection using external obliques vs. lumbar erectors, and the torque one creates at the hip and knee using glute max vs. glute med and inner hams and quads vs. outer hams and quads make a difference? Should a squat be performed in internal or external torque of some or all of the aforementioned muscles? Or both, depending on the phase of the squat?
Great questions Beau! So the lumbar spine will almost always have more torque placed on it than the thoracic spine due to the increased length of moment arm placed on those segments compared to the thoracic spine (which is closer in proximity to the placement of the bar). The only exception would be during a front squat, where the bar placed on the chest would create a longer moment arm for the thoracic spine compared to say a high bar back squat of the same weight.
The erectors will be the main area of concern when talking about overcoming joint torques during the squat compared to the obliques as the erectors are faced with the challenge of limiting lumbar flexion. The obliques are still very important but play more of a less important stabilizing role.
I’ll have some more articles later this year that will touch on the other questions in a much more complete manner. Thank you for checking out the article – I really appreciate it
I Think mine squat is quad dominant. I have a question: I’ve been through a surgery to correct a L4-L5 lumbar hernination. I would lime to know how many time I have to wait until start squating again with security and what is the best way to prepare myself to it! Thanks!
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Great question Isabella. It’s really going to be based on a number of factors – have you started working with a physical therapist yet?
Hi, love the content. Only 1 question. During upward phase you say rectus femoris shortening at the hip and lenghtening at the knee joint. İsn’t the opposite happens? Pardon my english:)
Great catch – definitely a typo on my part!
> Mechanically, our bodies can squat more weight when the lever arm is longest at the hips
It doesn’t make sense to me. Shouldn’t it be harder to lift a given weight the longer the lever arm gets?
I know you said that there isn’t a difference in quad activation between the front squat and back squat. However, as you said, there is more torque placed on the knee during front squats than back squats. Although the activation is the same between front and back squats, could the increase torque on the knee during front squats develop a different part of the quadriceps than during back squats? I guess what sparked this question is that grip width during lat pulldowns targets different parts of the lats. I realize that the anatomy of the lats are completely different than the anatomy of the quadriceps. I just was curious if something similar happens between the front and back squat seeing how there are torque differences between the two squat variations. Thank you for the article. The content is great!
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[…] Is Your Squat Quad or Hip Dominant […]
Hmmm… Maybe Greg’s theory on driving the hips under the bar at the sticking point will help me break 310# on my back squat…
[…] What this means is the “stripper squat” isn’t caused solely by a lack quad strength but rather due to problems in coordination and motor control that leads to a disruption in “lombards paradox”. […]
Does this also apply on low bar vs. high bar squats?
[…] #4 Is Your Squat ‘Quad Dominant’ or ‘Hip Dominant?’ […]
One of the most in depth guides I have seen on squat biomechanics. I have those same adipowers by the way–love squatting in them!
[…] https://squatuniversity.com/2017/08/08/is-your-squat-quad-dominant-or-hip-dominant/ […]
Any idea why do I get greaters DOMS in quads in front squat? (with similar or even less training volumen and/or relative intensity)
Maybe just a different pattern of quads?
[…] Is Your Squat “Quad Dominant” Or “Hip Dominant?” Posted on August 8, 2017 by Dr. Aaron Horschig squatuniversity.com “..Imagine now someone tied a rope around the same 10 lb. dumbbell and attached it to your elbow. It would now be much easier to hold your arm in front of you. This is because the length of the lever arm decreased, which meant there was less force (torque) required by the shoulder to keep the arm extended. Make sense? […]
[…] Aaron Horschig (2017) Is your squat quad dominant or hip dominant? https://squatuniversity.com/2017/08/08/is-your-squat-quad-dominant-or-hip-dominant/ […]
Feels just the opposite to me. With the weight in front I am able to sit back a little more
on my hams and glutes whereas when the weight is behind my neck I’m pushed more forward onto my quads.
There is “scientific” evidence and then there is empirical evidence. For DECADES, bodybuilders have been doing hack squats for blooming out the quads. In effect, it is like doing leg extensions while standing. Since a front squat is closer in form to a hack squat than the back squat, wouldn’t that indicate that front squats DO emphasize the quads more as proven by thousands of bodybuilders over the years? Ask Arnold Schwarzzeneger. Perhaps the “scientists” aren’t as familiar with weightlifting as they should be and are reaching conclusions based only on how much a muscle has “fired” during exertion.
I have been lifting for over 20 years so needless to say I am over 40. I have developed an issue recently that will require the advice of sports mechanics expert but thought to ask you as I came over this site through a search.
Even at my age and occasional joint pain I was still able to squat 2 -3 plates (45lb plates) each side for 8-10 reps. Don’t go heavier for safety sake.
But recently even with one plate I cannot go even close to half a squat without my quads pulling tight and hurting and it starts at upper quads just under pelvis.
But for some reason if I do a front squat I can manage 8-10 reps full and possibly 2 plates aside for 3-4. Is this an issue with posture? I cannot figure it out since I have never had a problem besides a couple severe pull 20 years ago.
Also my leg press load has also decreased since almost as if I am losing strength in my quads complete. Would appreciate any insight into this and your advice?
This way amazing 😍
Well that enlightened me. I too was of the mind that front squats were more quad-dominant and therefore stress the quads more. Thanks for the info here guys!
Would love to pull on the thread for front vs back squat a little more. Sort of going off topic in terms of hip vs. quad dominance, but what about the difference in compression on the joints?
I ask because we know that front squats provide similar muscle activation, but they require much less compression forces on the knee. And we know that there are no significant differences between the lifts (as found in your citation #12 from Dr. Contreras and Dr. Schoenfeld).
So if you are able to achieve similar results with either variation, yet you can reduce the compression forces on the knee, wouldn’t it be ideal to see the front squat utilized more in training programs?
Personally, I prefer front squat for that reason. It’s awesome when you can throw up plates on the back squat, but if I can achieve similar muscle activation with less stress on the knees, I’m all for it.
[…] Squats target the erector spinae, glutes, and hamstrings. Basically, it’s a hip dominant movement. It emphasises less on the quadriceps […]
Great article, thank you. So following the thought process of hip extension helping to extend the knee, this can also apply to plantar flexion? At the bottom of the squat, the ankle is dorsiflexed and returns to neutral via plantar flexion as the hip/knee extend. So the plantar flexors can assist in coming out of the squat? And would the ideal be optimal distribution of load among all three joints?
[…] Additionally, exercise-choice should focus on compound movements, with a balance of hip-dominant and quad-dominant exercises. […]
Front squats do actually work the quads more, as has been pointed out in this article via “greater torque” on (and, physics-wise, thereby “greater work” done by) the knees and hence the quads, particularly via the simple non-biarticulate vastus complex that simply just does knee extension. Claiming near-equivalent “EMG/activation” of quads between back and front squats only masquerades around the fact that within that same “activation” the quads (at the vastus complex, 3/4 of the quads!) actually do have to do more work, physics-wise! In other words, the front squats can well condition the quads to still “do more work” and “exhibit greater strength” even within “a same, given amount of EMG activation” (meaning, EMG activation doesn’t really tell you the whole story!).
Regarding the “good morning” back squat — I’d say that might be exhibited sometimes as “protective measure” against knee pain where the lifter, consciously or subconsciously, tries to specifically shift weight *away from* the knees (in order to protect them) and over to the hips/posterior chain, which is likely stronger the than quads anyway (i.e., hip extension w/glutes + hamstrings is stronger than quads / knee extension). Front squats prohibit this “transfer” from happening, and *force* the lifter to really lift using his/her legs using proper *squat* (not deadlift / “good morning”) form. And not only that, but by *forcing* this form, front squats also “force” more torque on the knees (as mentioned in this article) and thereby can likewise “load” the knee joint more strongly to enforce a likewise stronger, tighter, more coordinated, and less sloppy motion of the knee joint that can actually in turn likewise “strengthen” the knee joint even more (or even help fix a looser, less coordinated, sloppy one too!). It not that surprising, really — sometimes you have to really “load” the muscles related to a joint quite a lot in order to actually force that joint to move in a tighter, more coordinated, and less sloppy fashion…
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Nice article, altough I noticed some points:
EMG: Same EMG activity does not equal “same training effect”. i.e. Front squat: Quads and Glute may both have same EMG but quads may have more ROM and more raw stimulus (= Torque =r x Force) because of biomechanics in the front squat position. Summary: Two muscles may have similar EMG activation but different force production.
Torque = raw stimulus: Torque is defined as “Force times distance” T=r x F . Therefore more torque on the quads means more “training effect” (stimulus) of the quads.
Closed chain exercise: There is clearly more torque comparatively placed on the knee joint during a front squat (Horschig 2017). While quads and glutes always work together, glutes can support the quads in the front squat suboptimal. i.e. while one COULD perform a hip dominant front squat it would be coordinatively quit challenging… therefore most athletes will use their quads more in a front squat.
ROM: Quads have more range of motion in the deep front squat and more ROM means more training effect on a muscle group. Hip extensors (=glutes) have less ROM in the front squat because of lumbar angle.
EMG activation of quads: Your sources indicate there actually IS more activation of quads in the front squat: Yavus (2015) “Results may suggest that the front squat may be preferred to the back squat for knee extensor development and for preventing possible lumbar injuries during maximum loading.”
Do front squats train the quads more than the back squat? YES the do, and hack squats train the quads even more…
Looking forward to an updated version of this article.
PS: Read your book – liked it.