Popular Biomechanics

By Mark Rippetoe

In Powerlifting

March 01, 2007

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In Popular Bicomechanics Mark Rippetoe of Wichita Falls Athletic Club/CrossFit Wichita Falls says there are objective ways to describe proper form for the basic barbell exercises that are valid for everybody who does them, regardless of their anthropometry.

Any correct pull from the floor—for deadlift, clean, or snatch—will start with the bar directly under the scapulas and against the shins, regardless of your femur or back length. It is also a fact that a squat is only in balance when the bar is directly over that same middle one-third of the foot. If the bar path is vertical, two other squat variables can be analyzed. The angle of the back—that is, the general plane of the torso—will vary with the position of the bar on the torso, either on the back for a back squat or on the frontal deltoids for a front squat. Another immutable criterion for correct form is that your thighs will be aligned with your feet.

These criteria are based on skeletal considerations that do not vary, even though the individual expression of these criteria will. There are many ways to screw up the lifts, but an understanding of what we should be looking for at crucial places in the movements reduces the number of ways we are likely to do so. It also gives us some objective anatomical data on which to base our discussions of good form and best practices for lifting.

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8 Comments on “Popular Biomechanics”


Jason wrote …

Read a biomechanics article... The knees should not pass the toes when doing squats.


Coach wrote …


You didn't pick that up from a biomechanics article; you learned it from a dimwitted aerobics instructor who likely struggled with geometry and certainly had no exposure to biomechanics. The notion that the knees shouldn't pass beyond the toes is biomechanical nonsense. You are an arrogant fool. What you describe is impossible for most people's geometry. Stick around and learn something.

Welcome to CrossFit.


Robert wrote …

"You are an arrogant fool"

What a nice, welcoming environment.


wrote …

Coach has a point though-so many people are taught that the knee should never go in front of the ankle-they teach it on personal training courses here in the uk too-and of course it's rubbish, as was my course!


wrote …

A bit of a tangent - regarding form when performing barbell or dumbell squats: What of knee injuries and the PT tech or the doctor who cautions - regardless of the quadriceps drill, don’t allow the knee flexion angle to pass 90 degrees-a right angle- between the thigh and the shin.

Is the doctor correct to say such a thing?

Just want to know...last thing i'd want to do is try it and blow out the knee[!]


wrote …

Chris, Sorry it took me so long to answer.
Eh,how are your ACLs? There is minimal tension on ACLs up to 90 degrees knee flexion. The amount of forward knee shift in the squat is not as important as the tracking. For instance, the knee cap (patella) should track over somewhere around the large toe and first interspace. An example of poor knee alignment is posted below in the picture associated with the article, CrossFit & Powerlifting, by Jason Bagwell - May 05 CFJ> Note the knee valgus (knee falling in) on her right knee.
The key issues that are more important are knee tracking, flexibility, appropriate glute max/hamstring coactivation, and position of load. If knee tracking is correct more forward translation of the knee can be tolerated.
By the way, a parallel squat is to 100-110 degrees knee flexion


replied to comment from Jason


Please offer the biomechanics article that reports the knees should not pass the toes. I'd like to read it.

All the articles I have read regarding knee stress and squat depth state that the stresses at full extension are low and increase as squat depth increases. The willingness of the article to allow a deeper squat depends merely upon the authors choice of how much stress is "too much". Frankly, the stresses, anterior and posterior shear, in the joint are balanced in a healthy squat and allow the proper instantaneous axis of rotation. It is OBVIOUS that stresses will increase as the depth increases. Stress on the musculature increases as well, and properly applied stress allows healing of the tissues to withstand greater forces later; this applies to muscle, cartilage, and connective tissue. I don't believe everyone needs to immediately stand up and squat bottom-to-ground right now (that would be imprudent and dangerous, the tissue capacity in some individuals would be too low), but I think we would have a healthier population if everyone was consistently making steps toward that ability.

Evidence does show that ligaments are stretched as knee flexion angle increases. Why is this a problem? It is a problem if your belief is that the ligament acts as a strap to hold things together. This makes little sense as muscular tension will far surpass the tension capable by ligaments. We need to see ligaments instead as mechanoreceptive devices. They are position sensors for the nervous system allowing aiding neuromuscular control. Despite the evidence that deep squatting has the greatest stretching effect on knee ligaments, the article below stated that successful competitive olympic weightlifters had "tighter knees" than any of the other groups studied. These weightlifters move heavy loads out of a deep squat on a regular basis yet were more stable and precise through all ranges of motion.

Chandler, T. J., G. D. Wilson, and M. H. Stone. The effect of the squat exercise on knee stability. Med. Sci. Sports Exerc. 21: 299–303, 1989.

An interesting note, is that this article was from 1989. An article posted in the same journal in 2001 (ESCAMILLA, R. F. Knee biomechanics of the dynamic squat exercise. Med. Sci. Sports Exerc., Vol. 33, No. 1, 2001, pp. 127–141.) actually cited the Chandler article, but disregarded the evidence in it and still suggested that deep squats should not be performed and parallel squats are, in essence, good enough.

The knees go in front of the toes if the femur and torso length require it. The knees to should never adduct and go inside the toes, as stated above.


wrote …

I was having a discussion with the manager of one of my gyms ( a self proclaimed "expert" in bodybuilding). He claims that close stance, heels off the floor, toes forward front squats is the "absolute best" for building size in the quadricep muscle (mainly the teardrop and the muscles above the the kneecap). I didn't agree, but I'm not an expert. I was wondering if anyone could help with this discusion.

Thanks in advance

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