Shin angle relative to the vertical axis
Not only in the squat but in many other lower-body exercises, the angle of the shin relative to the vertical axis is one of the most important factors determining which body part, or which muscles, we end up working harder. The pictures show exactly what is meant by this shin angle. Focusing primarily on the squat for now: the sharper the angle between thigh and shin becomes during the squat, the more we squat with the thigh, that is, the quadriceps (largely the rectus femoris), or “off the legs”, so to speak. If we do not lean forward from the hips but still want to reach squat depth, this is only possible because the knee travels forward, and the squat becomes less of a forward lean from the hips and more of a flexion at the knee joint. The rectus femoris is indeed the main knee extensor in squatting.
Fry (Fry et al. 2003) and colleagues found that when we restrict forward knee movement in the squat (small shin angle relative to the vertical axis), much of the training load shifts to the hips. If we want to spare the knees by keeping the shins almost straight during the squat, the effort for performing the squat, coming up with the barbell and keeping the body balanced has to come from the hip joints and the muscles that extend them. The more vertical the shins are during the squat, the more we have to lean the torso forward from the hips and push the butt back to stay balanced; otherwise the body’s center of gravity moves out of balance and we fall over backwards. The forward lean of the body, and its magnitude (the angle between thigh and torso), automatically determines how much the hip extensors take part in the squat.
A very good practical example of the relationship between shin angle (the angle of the shins relative to the vertical axis) and the forward lean of the upper body is what we get when we compare the powerlifting squat with the front squat. In the front squat, the knees travelling past the toes is unavoidable and pronounced, and the angle between shin and thigh is considerably smaller than in the powerlifting squat. Because the torso cannot lean forward very much from the hips without the body tipping over and losing balance, the hip extensors are not stretched out in the front squat as much as they are in the powerlifting squat with its large forward lean. The small forward lean from the hips and the knees passing the toes in order to keep the center of gravity automatically mean that the thigh, the quadriceps, makes the dominant contribution to coming up out of the squat.
Conversely, squatting in the powerlifting style encourages the knees not to travel forward, and the angle between thigh and shin stays essentially at 90 degrees, which is considerably larger than in the front squat. Because the barbell sits practically on the back and relatively low compared with the front squat, the torso has to lean forward from the hips quite a lot to keep the body balanced. All of this means a greater contribution from the hip extensors (the biceps femoris, the glutes, and in addition the spinal erectors) in the squat.
In pictures G and H we can see clear differences in the angle between shin and thigh in the front squat and the powerlifting squat. The red line running through the shin shows the shin angle relative to the vertical axis (blue line) in the two squat styles. You can also clearly see that the forward lean of the torso differs between the two squat styles. The powerlifting squat, with a relatively vertical shin and a forward-leaning torso, strongly recruits the posterior chain in the squat (because to straighten the body back up, you have to extend it back out of a large forward flexion). The front squat, with little forward lean of the body and a large shin angle relative to the vertical axis, demands a large contribution from the quadriceps in the squat.
In pictures I (powerlifting squat) and J (front squat) we can see how far the knees travel past the toes in the different squat styles.
Foot position
Escamilla (Escamilla et al. 2001) and colleagues found that a wide stance in the squat, and likewise a high foot placement in the leg press, increase hamstring activity compared with a narrow-stance squat and a low foot placement in the leg press. Unfortunately, glute activity was not measured in any of the cases. Many other studies have also concluded that different foot widths and positions change and influence the proportion, structure and contribution of the different muscles that take part in the work. In the squat it is clear that the wider the stance, the more the squat can be seen as an extension at the hips. The narrower the stance in the squat, the more the squat involves, in parallel with hip extension, knee extension as well.
In pictures M and N we can see that with a wide stance the angle between torso and thigh is much smaller than with a narrow stance. In other words, with a wide stance we have to lean the body forward considerably more to stay balanced. A narrow stance in the squat, because of the small forward lean of the body, puts the emphasis on the quadriceps.
Summary
An interesting story. For many it probably contained nothing new, but this analysis of the squat and its biomechanics was certainly, once again, a slightly fresh angle. In fact, this is almost a translation of the article “The Squat: Hip vs. knee”, though not quite a direct translation. I left out some parts and enriched the text a great deal with my own view and understanding of squat technique. Below is a summary of the text, which also explains why I gave the article this title… CHAIN REACTION.
And so it goes: when we start to squat, everything begins with how we take the barbell onto the back or the upper back. It all starts right there, because the bar position (its height on the upper back) dictates every important nuance there is to talk about in the squat. If we take the bar low, this automatically means that, if we do not want to fall on our a… while squatting, we have to lean the torso further forward from the hips to keep the body’s center of gravity. The more we lean the torso forward from the hips in the squat, the smaller the angle between torso and thigh becomes, the more the hip extensors are stretched out in turn, and the more the squat becomes an extension from the hips. The more the body is leaned forward, the greater the flexion at the hips. How do you extend a forward-flexed body back up??? With the help of the hip extensors, of course: the glutes and the biceps femoris. With a low bar position, in the interest of keeping the body and the center of gravity in balance, we cannot let the knees travel past the toes… a heavily loaded barbell on the back would simply push us forward and we would fall on our stomachs together with the weight. Couldn’t we keep the stance narrow even with a low bar position? What would happen then??? What would happen is this: if we take the bar low, we are forced to lean forward with the torso to stay balanced, but if the feet are close together, the forward lean of the body cannot happen to the necessary extent, because the thighs are in the way. Balance would be disrupted and we would simply fall over on our side again. Squatting with a low bar position and a narrow stance can also cause problems in reaching the required depth. We might still reach that depth when squatting under the conditions described above, but biomechanically such a position would be extremely inefficient, and you would probably not be squatting heavy weights like that. It therefore follows unambiguously that with a low bar position it would be sensible to automatically use a relatively wide stance as well.
If we want to squat with maximum emphasis on the thigh, meaning the quadriceps, the best option is the high-bar position or the front squat. In the front squat, the barbell rests on the front portions of the lifter’s shoulder muscles. If we tried to do a front squat the way a powerlifter squats, the weight of the barbell would pull us forward onto our face. We have to be able to squat down so that the body’s center of gravity and the weight of the barbell add up. If we front squat the way powerlifters squat, the weight of the barbell does not combine with the body’s center of gravity, and the two do not move in the same direction.
So the high-bar position and the front squat automatically rule out any forward lean of the torso while squatting, otherwise we would fall on our face. To keep the body’s center of gravity from losing balance, we have to squat with a relatively upright back and let the knees travel past the toes in order to complete the squat. Compared with a powerlifting-style squat, an upright torso and knees passing the toes automatically mean less work from the hip extensors and more work from the knee extensors during the squat. If we tried to do a front squat with a wide stance, as wide as in a powerlifting back squat, we would again lose our balance and fall.
So whether we squat with an emphasis on the quadriceps or on the hip extensors is already decided by how we place the barbell on our upper back.
Literature used in the original article:
1. Adams M A., Hutton W C. 1985: Gradual Disc Prolapse. Spine;10(6):524-531.
2. Burgess-Limerick R., Abernethy B., Neal R J., Kippers V. 1995: Self-Selected Manual Lifting Technique: Functional Consequences Of The Interjoint Coordination. Hum Factors. Jun;37(2):395-411.
3. Burgess-Limerick R., Abernethy B. 1997: Toward A Quantitative Definition Of Manual Lifting Postures. Hum Factors: 39(1):141-148
4. Caterisano A., Moss R F., Pellinger T K., Woodruff K., Lewis V C., Booth W., Khadra T., 2002: The Effect Of Back Squat Depth On The Emg Activity Of 4 Superficial Hip And Thigh Muscles. J Strength Cond Res. Aug;16(3):428-32.
5. Chek, Paul. 2002: Scientific Balance Training, Personal Training on the Net. USA
6. Escamilla R F., Fleisig G S., Zheng N., Lander J E., Barrentine S W., Andrews J R., Bergemann B W., Moorman C T. 3rd. 2001 Effects Of Technique Variations On Knee Biomechanics During The Squat And Leg Press. Med Sci Sports Exerc. Sep;33(9):1552-66.
7. Escamilla R F., Francisco A C., Kayes A V., Speer K P., Moorman C T. 3rd. 2002: An Electromyographic Analysis Of Sumo And Conventional Style Deadlifts. Med Sci Sports Exerc. Apr;34(4):682-8.
8. Escamilla RF, Fleisig GS, Zheng N, Barrentine SW, Wilk KE, Andrews JR. 1998: Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises. Med Sci Sports Exerc. 1998 Apr;30(4):556-69.
9. Farfan H F. 1975: Muscular Mechanism Of The Lumbar Spine And The Position Of Power And Efficiency. Orthop Clin North Am ;6(1):135-144.)
10. Fry A C., Smith J C., Schilling B K. 2003: Effect Of Knee Position On Hip And Knee Torques During The Barbell Squat.. J Strength Cond Res. Nov;17(4):629-33.
11. Decker M J., Torry M R., Wyland D J., Sterett W I., Richard Steadman J. 2003: Gender Differences In Lower Extremity Kinematics, Kinetics And Energy Absorption During Landing. Clin Biomech (Bristol, Avon). Aug;18(7):662-9.
12. Kendall, Florence Peterson., McCreary, Elizabeth Kendall., Provance, Patricia Geise. 1993: Muscles Testing and Function 4th Edition, Lippincott Williams and Wilkins. USA
13. King, Ian J. 2000: How to Write Strength Training Programs 2nd Edition, Kingsports International Publishing
14. Mancino, Mark. 2003: What’s The Pelvis Got To Do With It? Kinetic Advantage Inc., Canada
15. McCaw S T., Melrose D R., 1999: Stance Width And Bar Load Effects On Leg Muscle Activity During The Parallel Squat. Med Sci Sports Exerc. Mar;31(3):428-36.
16. Netter, Frank H. 1989: Atlas of Human Anatomy, Novartis, USA
17. Piazza S J., Delp S L., 1996: The Influence Of Muscles On Knee Flexion During The Swing Phase Of Gait. J Biomech. Jun;29(6):723-33.
18. Ridderikhoff A., Batelaan J H., Bobbert M F. 1999: Jumping For Distance: Control Of The External Force In Squat Jumps. Med Sci Sports Exerc. Aug;31(8):1196-204.
19. Rouse, Peter. 2003: Integrated Flexibility Manual, Functional Integrated Training Systems. Australia
20. Russell P J., Phillips S J., 1989: Preliminary Comparison Of Front And Back Squat Exercises. Res Q Exerc Sport. Sep;60(3):201-8.
21. Sahrmann, Shirley A. 2002: Diagnosis and Treatment of Movement Impairment Syndromes, Mosby, USA
22. Scholz J P., McMillan A G. 1995: Neuromuscular Coordination Of Squat Lifting; Individual Differences. Phys Ther 75(2):133-144.
23. Siff, Mel C. and Verkhoshansky, Yuri V. 1993: Supertraining: Special Strength Training for Sporting Excellence, School of Mechanical Engineering of the Witwaterstrand, Johannesburg, South Africa.
24. Wang M Y., Flanagan S., Song J E., Greendale G A., Salem G J. 2003: Lower-Extremity Biomechanics During Forward And Lateral Stepping Activities In Older Adults. Clin Biomech (Bristol, Avon). Mar;18(3):214-21.
25. Wretenberg P., Feng Y., Arborelius U P., 1996: High- And Low-Bar Squatting Techniques During Weight-Training. Med Sci Sports Exerc. Feb;28(2):218-24.
26. Hanna. T. 1988: Somatics; Reawakening the Mind’s Control of Movement, Perseus Books. USA.
Translated by Janar Rückenberg
Come and train! ArtGym
