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Mechanics of Squatting

Quick Hit Summary

The squat is a favorite exercise for many hard core resistance athletes. Recent research has provided an interesting look at squat mechanics. It appears that it’s OK if your knees extend over your toes during the movement (within reason of course). The key thing, with respect to preventing injuries, is weight distribution on the foot. Also, when squatting with the same relative loads (70% 1RM) front squats appear to reduce the compressive stresses on the knee vs. the back squat. As a final note, don’t forget to consciously explode out of “the hole” while squatting. Even if they weight is heavy (ie 1RM or 3 RM) one should attempt to push the weight as fast as possible.


Figure 1 The back squat10

Squats… is there another exercise that drills the body quite like heavy squats? Subjectively speaking, outside of maybe deadlifts, I’m guessing probably not. Although Romanian deadlifts are my favorite lift, they are closely followed by squats. After a good squat workout, especially an intensive one that brings about a good muscle pump, I feel like the Incredible Hulk, waiting to burst out of my “suddenly too small” gym attire! {To save a few eyebrows from being raised, when I say “suddenly too small”, I’m referring to the fact that I mentally feel as if my muscles are bursting through my clothes (a la Incredible Hulk)… Not that I work out in clothes purchased at GAP Kids ® as I sometimes feel other “muscular” resistance trained individuals do!!!}. Within the past year, there have been some interesting studies published on the biomechanics of squats. Although some of these studies simply confirm what power athletes may already know, others serve as good reminders on how to properly execute the lift. Without any further digressions, I’d like to share with you recently published research regarding squat mechanics.

Recently Published Research Regarding the Squat Exercise

Study #1

Miletello et al. examined how squat mechanics differed between individuals with various experience performing the back squat1. Their study compared 9 collegiate competitive lifters (most of whom placed at the 2006 U.S. Collegiate National Championships; mean age- 20 years), 9 competitive high school lifters (most of whom placed at the 2006 Louisiana State High School Powerlifting Championships; mean age- 17) and 11 novice powerlifters (mean age-20) who had < 6 months of training experience. Each lifter performed their approximate 1 rep max without the use of wraps or squat suits. The main difference noted between groups was that collegiate lifters had a much faster acceleration out of the bottom squat position (ie-firing out of the hole) vs. both the high school and novice lifters.

From a practical standpoint, many individuals (including myself from time to time), often forget to consciously “explode” out of the hole while squatting. This has implications for all individuals, especially those competing in sport. The greater acceleration one has coming out of the bottom position in a squat exercise, the more momentum they have to help carry them through the “sticking point” during the exercise. Thus, one is able to lift more weight. Regardless of the weight (1RM, 5RM, etc), one’s goal should always move the weight as fast as possible. As mentioned by Dr. Digby Sale, one of the foremost authorities on neuromuscular influences on resistance training.

“When the intent is to contract the muscle as fast as possible with the maximum rate of force development, motor units begin firing at a very high frequency…”2 which leads to, “an increase in rate of force development”2

In layman’s terms, when you consciously try to move fast (even if you’re physically not moving fast), your muscles contract more powerfully. Indeed, a few studies have shown that following a resistance training program (where relative training intensity was held constant between fast and slow training groups), the intention to lift as fast as possible led to greater rate of force development/power [3]4. One caveat worth mentioning with those studies is that one was completed in an elderly population3 and the other was completed in novice resistance trained athletes4. Despite these study drawbacks, my personal experience while training athletes seems to agree with the results obtained in those studies.

Study #2

Paoli et al. studied the effects of stance width and foot position on 8 muscles of the thigh (including ones composing the quadriceps, hamstring, butt muscles)5. Experienced weightlifters completed back squats (3X10) with a narrow stance (~ hip width, feet pointed straight ahead), intermediate stance (~150% of hip width), and a wide stance (~200% of hip width; feet angled outward at 45º angle). All squats were completed at 70% of single rep max (1RM) as the researchers stated that “this is often selected in training programs.” After completing all trials, it was found that only the gluteus maximus (main muscle in butt) was affected by stance width. In comparison to a narrow stance, wider stances increased muscle activity of the gluteus maximus. Paoli et al. also found foot placement (straight in narrow stance vs. outward angled in wide stance), did not selectively activate specific muscles of the quadriceps (vastus lateralis, rectus femoris, vastus medialis). See Figure 2.

Figure 2 Individual muscles of the Quadriceps. The vastus lateralis is the most lateral of the quadriceps muscles highlighted in this picuture. The rectus femoris is middle quadricep muscle and the vastus medialis is the innermost of the muscles. Picture obtained from commons.wikimedia.org/wiki/File:Quadriceps.png.

From a practical standpoint, if you want to increase gluteus activation/strength, go with a wider stance. In my opinion, the most interesting finding of this study was that no difference was observed in quadriceps activation between the narrow and wide stances. Additionally, the angle with which ones feet were pointed did not influence activation of various quadriceps muscles. Various bodybuilding magazines/books often claim that different stance widths/foot placements influence how hard the individual quadriceps muscles are worked. In particular, one popular book claims that narrow stance squats, with feet pointed straight ahead, increases activation of the outer, vastus lateralis aspect of the quadriceps6. Furthermore, this same piece of literature indicates that wide stance squats (with feet pointed out) preferentially works the inner, vastus medialis portion of the quadriceps. This popular body building myth is clearly contradicted by the work of Paoli et al.5 and other research teams7.

One could play a devil’s advocate and point out that Paoli et al had individuals complete this lift at 70% 1RM. Maybe, differential quadriceps activation only occurs at higher training intensities such as 85-95% 1RM. However, as explained by McCaw & Melrose7, differential activation of the individual muscles of the quadriceps muscles doesn’t make sense from an anatomical perspective.

“The results of this study suggest the three components of the quadriceps perform as a group regardless of concentric or eccentric activation during varied stance and load conditions. Because the vastus medialis and vastus lateralis are uniarticular muscles, crossing only the knee joint, varying stance width by altering thigh position in the frontal plane would not affect the length of the muscles, a factor that could influence recruitment patterns and magnitudes. The lack of a significant stance width effect on IEMG values for the rectus femoris suggests limited physiological implications of any change in the length of this biarticular muscle that may occur when hip position varies within the altered stance widths used in this study”7.

For reference, uniarticular simply means a muscle extends over a single joint. For this study, the vastus lateralis & medius start on the femur bone, cross the knee joint, and attach into the tibia (main lower leg bone). Biarticular refers to the fact that a muscle crosses 2 joints. In this case, the rectus femoris starts on the pelvis, crosses hip joint and then passes over the knee joint before connecting into tibia.

Study #3

The front and back squat are probably the two most common squat variations used by ball/speed sport athletes. Recently, Gullet et al examined the biomechanical differences between these 2 lifts8. The study included 15 experienced lifters (9 men, 6 women) who had been training with each lift at least 1x/week for a > 1 year. During separate trial days, each lift was completed at the same relative training intensty (70% 1RM). After analyzing the data, it was found that front squats, vs. back squats, had lower compressive stresses, but equal shear stresses on the knee joint. In the knee joint, one’s cruciate ligaments (ie-anterior & posterior cruciate ligaments which are commonly referred to as the ACL/PCL) are responsible for “handling” this stress. In contrast, the hyaline cartilage and meniscus tissue are responsible for absorbing compressive forces. Please refer to Figure 3 for explanation on these forces. Despite lifting more weight with the back squat, muscle activation was the same for the hamstring (biceps femoris, semitendinosus), quadriceps (rectus femoris, vastus lateralis, & vastus medialis) and spine (erector spinae) muscles. It should be noted that the butt muscles (gluteus maximus, etc) were never tested.

Figure 3 Various types of Stress. The red arrows indicate the direction from which the force is being applied. The left hand figure represents compressive stress. This type of stress occurs when 2 objects are being smashed together. In the above picture, the top box is being pushed into the bottom box (which is also being pushed into the top box). The right hand figure represents shear stress.This type of stress occurs when two objects are rubbing past each other. An example of shear stress would be rubbing your hands together when you are cold. Image created by Sean Casey.

This study provides an interesting look at squat mechanics. At 70% of 1RM, no differences were found in muscle activity8. {Again I want to stress that the gluteus/butt muscles were not tested in the trial. If these muscles were tested, I'm pretty sure it would show far greater activation levels during the back squat}. Although squat variation did not appear to affect stress on structures such as the ACL/PCL, higher compressive forces were found while performing the back squat. As a result, more stress would have been put on the meniscus and hyaline cartilage. This has large implications for someone with a medical history of problems associated with these structures. With similar muscle activation between exercises (excluding the gluteus maximus), and lower stresses on the knee, individuals with preexisting cartilage and meniscus issues may be better off including more front vs. back squats in their exercise routine.

Regarding front squats… Many individuals struggle with this exercise due to limited shoulder and/or wrist mobility. If you find yourself in this category, work on stretching the large latissimus dorsi (a.k.a.- “lats”) muscles of your back. Also, look into using wrist straps. As a FYI, I have no financial or career related connection with the website that comes up if you click on “wrist straps” in the previous sentence. Rather, it was the first good link I could find with good example pictures of an individual using wrist straps.

Study #4

While coaching the squat, many instructors commonly use the phrase, “don’t let your knees go over the toes.” In fact, while in high school, I used to give this cue to my fellow football teammates while spotting them during the squat. Why did I say this? Quite frankly, I used this phrase simply because I was told that one would be develop knee problems if they squatted in this fashion. However, my stance on the knee issue has changed during the past 8-10 years as I obtained more experience working and began to further examine the biomechanics of the squat. In a study completed by Fry et al., researchers examined the effects of limiting knee movement (in the anterior direction) during back squats9. Participants squatted under the following 2 conditions:

  • Normal Squat
  • Restricted squat- vertical board placed anterior edge of foot, preventing knees from drifting beyond toes.

Torque on the knee decreased during the restricted vs. normal squat. However, during the restricted squat, torque increased on hips and an exaggerated forward lean with the upper torso. Thus,

“It thus becomes a trade-off between optimal knee positioning and optimal hip and back positioning. While it is critical to protect the knees from unnecessary forces, it is also important to avoid unnecessary forces acting at the hips. These hip forces will ultimately be transferred through the lower back and therefore must be carefully applied. The net result is that proper lifting technique must create the most optimal kinetic environment for all the joints involved.”9

In applying this information, I’m not quite as adamant as I once was regarding the knees going over the toes during squats. Please don’t misunderstand my comment, I’m not saying that one’s knee should extend WAY past their toes during the exercise!!! I’m simply saying that in order to optimize hip/low back mechanics, allowing one’s knees to drift over their toes is necessary for some athletes depending on their anthropometrics. This is especially true for tall, long limbed athletes. Yes, you could force them to keep their lower leg (tibia) relatively perpendicular to the ground, but you’ll usually find 2 things- They lose their balance and/or get sore backs.

When coaching the squat, my primary concern is not how far their knees travel over their toes. Rather, I’m focused on how the weight is distributed on their foot. One should always have the weight distributed from the balls of their feet back through their heel. For those who learn best via mental images, think of a “power arrow” with the base at the balls of your foot and the peak pointing towards your heal (Figure 4). When this arrow is pointed the opposite way (ie- towards your toes), the load is shifted onto structures within the knee joint, increasing the risk of injury. As a quick coaching cue, I'll sometimes tell athletes to "push through their heels" simply to reemphasize that we don't want the weight distributed over the front part of their foot.

Figure 4 Power Arrow. This arrow should start at the balls of your feet and extend back towards your heel. When this arrow reverses direction, the likelihood of injury increases dramatically. Please not that this should also be how force placement should be during various deadlift variations. Image created by Sean Casey.

In attempting to squat to parallel, many individuals shift the weight over the front (anterior) end of the foot. As aforementioned, this increases stress on the knees. What can one do to prevent this from happening? First, work on ankle mobility. If one has stiff ankles, they’re limited in their ability to dorsiflex their ankle. In turn, one often compensates by shifting the weight onto their toes and/or rounding their back. See Figure 5 for movements at the ankle.

Figure 5 Movements at Ankle. The dorsiflexed ankle is one in which the foot is pulled up toward the shin bone. In the diagram, this is the “blue” foot. The plantarflexion occurs when the angle between the shin and the foot gets bigger (red foot position in diagram). This occurs when you jump into their air or stand on your toes. Image created by Sean Casey.

For those struggling with weight distribution there are a few things to work on.

  • #1. Curl your toes upward during your warm up sets. This will force you to push through the preferred power arrow discussed above. I’ve found this to be very effective as it “primes” your motor program prior to competing heavier sets.
  • #2: Focus on lowering your body by pushing your hips behind you vs. bending the knees. Speaking from experience, one’s first movement should be at the hips. If your first movement is at the knees, its pretty dang hard to maintain good squat form.
  • #3: As mentioned above, work on ankle mobility. I can't stress this enough. If you're stiff in the ankles (especially dorsiflexion) you'll likely compensate by either shifting the weight towards your toes and/or rounding the back.
  • #4: Put weight plates (2 ½ or 5 lb plates usually work well) under your heels. Due to the biomechanics of the squat, this allows you to squat near parallel while still pushing through the preferred power arrow.

Bottom Line

These studies provide interesting commentary on squat mechanics. The take home points I gathered from each of the above studies are as follows:

1). Explode out of the bottom “hole” position during the squat. Even if the weight is heavy, attempt to move it as fast as possible.

2). Don’t get caught up in old body building myths which claim that narrow vs. wide squat stances preferentially affect certain muscles of the quadriceps. Human anatomy prevents this claim from even making sense!

3). Save your knees by performing more front squats… especially if you have a history of cartilage or meniscus issues.

4). Within reason, it’s “OK” to let your knees extend over your toes while squatting. Focus your attention on weight distribution on your foot. Focus on lowering your body by pushing your hips behind you (vs bending at the knees).

Good luck as you continue to develop into a squatting machine!

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1 Miletello WM, Beam JR, Cooper ZC. A biomechanical analysis of the squat between competitive collegiate, competitive high school, and novice powerlifters. J Strength Cond Res. 2009 Aug;23(5):1611-7.

2 Sale D. “Neural Adaptation to Strength Training.” Strength and Power in sport. 2nd ed. Komi P.V. Blackwell Publishing Company. Malden MA. 2003. 282-283. Print.

3 Fielding RA, LeBrasseur NK, Cuoco A, Bean J, Mizer K, Fiatarone Singh MA. High-velocity resistance training increases skeletal muscle peak power in older women. J Am Geriatr Soc. 2002 Apr;50(4):655-62.

4 Young, W.B., Bilby. GB. The effect of voluntary effort to influence speed of contraction on strength, muscular power, and hypertrophy development. J. Strength. Cond. Res. 7:172– 178. 1993.

5 Paoli A, Marcolin G, Petrone N. The effect of stance width on the electromyographical activity of eight superficial thigh muscles during back squat with different bar loads. J Strength Cond Res. 2009 Jan;23(1):246-50.

6 Schwarzenegger, A and Dobbins, B. The Arnold Schwarzenegger Encyclopedia of Modern Bodybuilding. New York: Simon and Schuster, Inc., 1985.

7 McCaw ST, Melrose DR.. Stance width and bar load effects on leg muscle activity during the parallel squat. Med Sci Sports Exerc. 1999 Mar;31(3):428-36.

8 Gullett JC, Tillman MD, Gutierrez GM, Chow JW. A biomechanical comparison of back and front squats in healthy trained individuals.J Strength Cond Res. 2009 Jan;23(1):284-92.

9 Fry AC, Smith JC, Schilling BK. Effect of knee position on hip and knee torques during the barbell squat. J Strength Cond Res. 2003 Nov;17(4):629-33.

10 Created by Rexwar. Accessed June 14, 2010 from: http://en.wikipedia.org/wiki/File:Squat.png

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Written on April 14, 2010 by Sean Casey
Last Updated: September 29, 2013

This information is not intended to take the place of medical advice.Please check with your health care providers prior to starting any new dietary or exercise program. CasePerformance is not responsible for the outcome of any decision made based off the information presented in this article.

About the Author: Sean Casey is a graduate of the University of Wisconsin-Madison with degrees in both Nutritional Science-Dietetics and Kinesiology-Exercise Physiology. Sean graduated academically as one of the top students in both the Nutritional Science and Kinesiology departments.
Field Experience: During college, Sean was active with the UW-Badgers Strength and Conditioning Department. He has also spent time as an intern physical preparation coach at the International Performance Institute in Bradenton, FL. He also spent time as an intern and later worked at Athletes Performance in Tempe, AZ. While at these locations he had the opportunity to train football, soccer, baseball, golf and tennis athletes. Sean is also active in the field of sports nutrition where he has consulted with a wide variety of organizations including both elite (NFL’s Jacksonville Jaguars) and amateur athletic teams. His nutrition consultation services are avalable by clicking on the Nutrition Consultation tab.