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Fact Or Fiction — Are Full Squats Bad For Your Knees?

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The barbell squat: widely considered the most effective and comprehensive full-body exercise, it’s no wonder that this single movement is often deemed the “king” of all exercises.  In my experience, no lift comes close to firing up so many muscle groups, requiring such complete coordination and mental concentration, and just straight up beating the crap out of me as the barbell squat.  No matter what your fitness goal, squats will almost certainly help you achieve them. Want to build muscle? Do squats. Want to burn fat? Do squats. Want to simply be more awesome at everything? Do squats. I think you see where I’m going with this.

But while more and more people are realizing the benefits of squatting and incorporating them into their workouts, there still seems to be much debate over how deep one should squat in order to maximize the effectiveness of the workout while minimizing the risk of injury.

Before I continue, I’m going to define a term that I will be using a lot that seems to have different meanings to different people.  I personally believe a parallel squat to be a squat in which your hips and knees are at the same height, with your thighs running parallel to the ground, like Figure 4 below:

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But a lot of people and studies have seemed to define a parallel squat as one in which your knees are at 90o of flexion, like that of Figure 2.  So for purposes of discussion, let’s go ahead with what has historically been more often accepted as a parallel squat, aka one in which the angle formed between your hamstrings and knees is ~90o.  That’s what we’re going with, even though it’s NOT really correct.

With that out of the way, let’s continue. On one side of the argument, you have those who believe it is much better to squat past parallel, as you’re going through a more complete range of motion and taxing the muscles worked to a larger extent.  (A true parallel squat like that of Figure 4 would actually fall under this criterion, as it is in fact quite deep of a movement.)  Proponents for this type of squatting usually refer to it as a “full squat,” “deep squat” or “ass to grass (ATG)” squat.

In the other camp, you have those who believe that squatting to such a depth is dangerous, and thus people should only squat down to parallel at the VERY lowest. The reasoning used to support this argument is usually that going down so low is bad for the knees, and therefore one should only do half squats (45o of flexion), parallel squats (90o of flexion), or even…quarter squats (minimal flexion, makes you look like you’re twitching your legs like an idiot).

So who is right? How low should you really squat?

According to one study on squat depth biomechanics from the National Strength and Conditioning Association (NSCA), it seems that not only are full squats MORE effective for working your glutes but also SAFER on the knees. Research cited in the study has shown that muscle activity in the gluteus maximus (or, your butt) is significantly higher in the full squat than in parallel and partial squats. At the same time, the forces on your anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) actually DECREASE the deeper you squat.

Peak tension on the ACL occurs at 15o-30o of flexion (which is a quarter squat, I suppose?), decreasing significantly at 60o of flexion and then dropping off as you go even lower. At the same time, peak tension on the PCL occurs at 90o of flexion (parallel squat) and then decreases as you go subsequently lower.  In fact, it looks like a parallel squat is actually more detrimental to your knees than a full squat, as more pressure is placed on the PCL in this position.  Interesting, huh?1

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The anatomy of the knee joint

The conclusion is quite simple: full squats are NOT bad for your knees, and therefore you should squat deep.

Partial and parallel squats may hit the quadriceps and hamstrings enough, but if you really want to get your butt toned up and put yourself at lower risk of injury, try squatting lower into the hole. I understand that I’m basing most of this off of just one study, but plenty of other research has also shown that athletes who do full squats actually have increased knee joint stability and tighter joint capsules. You can even try it out for yourself. Stand up right now and try squatting down such that your hamstrings and calves form a right angle. Where do you feel most of the pressure? Now go down even lower so that the hamstring-calf angle is closer to 60o or 45o.  Where do you feel most of the pressure now? My point exactly.

With that said, however, one shouldn’t just run into the gym and start squatting as low as possible. If you haven’t been doing full squats and want to start, you need to take a number of precautions to do things right and prevent injury:

    1. Test how deep you can really go comfortably.  Not everyone has the hamstring and hip flexibility to drop down into a full squat, and if it takes multiple sessions for you to get comfortable with it and do it safely, then that’s your best plan of action.
    2. Try full squatting with minimal weight.  You’d be surprised just how much harder those extra 15o can make, so even if you can partial/parallel squat a lot of weight, start light…then work your way up.
    3. Make sure your lower back doesn’t arch too much at the bottom of the movement.  If it does, you’re going lower than your body will allow.  Due to biomechanics, most people’s lower backs tend to curve in slightly at the bottom of a full squat, which is often called a “butt wink.”  This is fine as long as it’s minimal, but if the curve is drastic, chances are your hamstrings and lower back aren’t flexible enough yet to be going so low, so scale back the depth just a little bit until you build the necessary strength and flexibility.
    4. And finally, as with any squat, make sure you’re utilizing proper form for the exercise.  Keep your head up and core tight, don’t arch your back, and drive from the heels while keeping your knees straight.  If you’re new to this, the video below does a pretty good step-by-step walkthrough:



So there you have it. Perform deep, full squats and your butt, quads, and hamstrings will be toned like never before, AND you’ll put your knee joints at decreased risk of injury. Plenty of people seem to have the perception that full squats are dangerous, but this is almost always based on outdated research and endless hearsay from “uneducated bros.”  Take a hard look at the science, feel free to dig up some more research if you’ve got the resources, and at the end of the day I suppose you can think of it like this:

Would you ever bench press halfway down? Would you feel content reading half a book, or running half a marathon? So why would you squat halfway down? You wouldn’t — and I can bet you this guy didn’t either. 

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Want to know how Arnold became an action star and the governor of California? He squatted like this.


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References, Notes, Links

  1. The Biomechanics of Squat Depth, NSCA Hot Topic Series, Brad Schoenfeld.

    2. Buchanan CI, Marsh RL. Effects of exercise on the biomechanical, biochemical and structural properties of tendons. Comparative Biochemistry and Physiology. Part A, Molecular and Integrative Physiology. 133(4):1,101 – 1,107. 2002

    3. Caterisano A, Moss RF, Pellinger TK, Woodruff K, Lewis VC, Booth W, and Khadra T. The effect of back squat depth on the EMG activity of 4 superficial hip and thigh muscles. Journal of Strength and Conditioning Research. 16(3):428 – 432. 2002

    4. Chandler T, Wilson G, and Stone M. The effect of the squat exercise on knee stability. Medicine and Science in Sports and Exercise. 21(3):299 –303. 1989.

    5. Escamilla RF, Fleisig GS, Zheng N, Barrentine SW, Wilk KE, and Andrews JR. Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises. Medicine & Science in Sports & Exercise. 30:556 – 569. 1998.

    6. Escamilla RF. Knee biomechanics of the dynamic squat exercise. Medicine and Science in Sports and Exercise. 33:127 – 141. 2001.

    7. Escamilla RF, Fleisig GS, Zheng N, Lander JE, Barrentine SW, Andrews JR, Bergemann BW, and Moorman CT. Effects of technique variations on knee biomechanics during the squat and leg press. Medicine and Science in Sports and Exercise. 33:1,552 – 1,566. 2001.

    8. Kanamori A, Woo SL, Ma CB, Zeminski J, Rudy TW, Li G, and Livesay GA. The forces in the anterior cruciate ligament and knee kinematics during a simulated pivot shift test: A human cadaveric study using robotic technology. Arthroscopy. 16(6):633 – 639. 2000.

    9. Klein K. The deep squat exercise as utilized in weight training for athletes and its effects on the ligaments of the knee. JAPMR. 15(1):6 – 11.1961.

    10. Li G, Zayontz S, DeFrate LE, Most E, Suggs JF, and Rubash HE. Kinematics of the knee at high flexion angles: an in vitro investigation. Journal of Orthopaedic Research. 27(6):699 – 706. 2004.

    11. Li G, Zayontz S, Most E, DeFrate LE, Suggs JF, and Rubash HE. In situ forces of the anterior and posterior cruciate ligaments in high knee
    flexion: an in vitro investigation. Journal of Orthopaedic Research. 22(2):293 – 297. 2004.

    12. Li G, Rudy TW, Sakane M, Kanamori A, Ma CB, and Woo SL. The importance of quadriceps and hamstring muscleloading on knee kinematics
    and in-situ forces in the ACL. Journal of Biomechanics. 32(4):395 – 400. 1999.

    13. Markolf KL, Slauterbeck JL, Armstrong KL, Shapiro MM, and Finerman GA. Effects of combined knee loadings on posterior cruciate ligament
    force generation. Journal of Orthopaedic Research. 14(4):633 – 638. 1996.

    14. Meyers E. Effect of selected exercise variables on ligament stability and flexibility of the knee. Research Quarterly. 42(4):411 – 422. 1971.

    15. Nisell R, and Ekholm J. Joint load during the parallel squat in powerlifting and force analysis of in vivo bilateral quadriceps tendon rupture.
    Scandinavian Journal of Sports Sciences. 8: 63 – 70. 1986.

    16. Panariello R, Backus S, Parker J. The effect of the squat exercise on anterior-posterior knee translation in professional football players. American
    Journal of Sports Medicine. 22(6):768 – 773. 1994.

    17. Sakane M, Fox RJ, Woo SL, Livesay GA, Li G, and Fu FH. In situ forces in the anterior cruciate ligament and its bundles in response to anterior
    tibial loads. Journal of Orthopaedic Research. 15(2):285 – 293. 1997.

    18. Signorile JF, Weber B, Roll B, Caruso J, Lowensteyn I, and Perry AC. An electromyographical comparison of the squat and knee extension exercises.
    Journal of Strength and Conditioning Research. 8:178 – 183. 1994.

    19. Steiner M, Grana W, Chilag K, and Schelberg-Karnes E. The effect of exercise on anterior-posterior knee laxity. American Journal of Sports Medicine.
    14(1):24 – 29. 1986.

    20. Wilk KE, Escamilla RF, Fleisig GS, Barrentine SW, Andrews JR, and Boyd ML. A comparison of tibiofemoral joint forces and electromyographic
    activity during open and closed kinetic chain exercises. American Journal of Sports Medicine. 24(4):518 – 527. 1996.



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