The Origins of “Don’t Squat Below Parallel!”

Background

Today many are accustomed to performing squats below parallel during their training, but there are still those who remember the old days when it was very common for both trainers and doctors to say that squatting below parallel was dangerous for your knees (to be totally honest, some still say this). I was asked by several of my clients to explain how this notion came about, and I wanted to get as much detail as I could, so I did some digging. It turns out that the credit for the notion that squatting below parallel is dangerous goes to Dr. Klein from the University of Texas. The study at the heart of it all is his 1961 paper in the J. Assoc. Phys. Ment. Rehabil. entitled “The Deep Squat Exercise Utilized in Weight Training For Athletics and Its Effects on the Ligaments of the Knee.”

Study Details

Experimental Design:

• The study is concerned with squatting during weight training (squats where a weight is lifted up and down).
• Initially 64 human cadaver knee ligaments (medial, lateral, anterior cruciate (ACL), and posterior cruciate (PCL)) were examined in different positions (standing, partial squat, deep squat). Cadaver measurements were made for ligament lengths before and after being pushed into a deep squat.
• 128 live humans were also examined including competitive weightlifters at the Pan-American Games (all had practiced deep squats) and 386 “control” humans who were from beginning weightlifting classes, basketball classes, and gymnastics classes (none had performed any deep squat exercises with weights).
• "Standard" orthopedic tests were used to determine ligament "status."
• Data from 95 paratroopers are placed in the conclusions section. Measurements were conducted as in the other groups and paratroopers were also compared to the same control group.

Results:

• The author states that, by looking at all the cadaveric group data, the medial and lateral ligaments are exposed to an abnormal stretch effect in a deep squat.
• For the weightlifter/control group comparison, the lateral ligament was exposed to a greater stretch than the medial ligament in the deep squat group.
• In addition, 19.4% more right lateral ligaments were unstable than right medial ligaments and 12% more left lateral ligaments unstable than left lateral ligaments.
• Deep squatters (weightlifters) had 56% greater medial ligament instability in the right leg and 58% more in the left leg, as compared to controls.
• Data from paratroopers showed no differences in ligaments when comparing their right and left legs, but overall their ligaments were weaker than those of the control group.

Limitations:

• The review of literature in the beginning discusses how the knee bones and ligaments behave in weighted squats, but this is not referenced – it doesn’t point to any actual studies.
• After measuring the “stretch” (difference in length for the ligaments above parallel and in a deep squat), the author states that, by looking at all the group data, the medial and lateral ligaments are exposed to an abnormal stretch effect in a deep squat. There is no justification for what a normal stretch would be.
• The control group isn’t a proper control group. It is mixed with individuals of different ages, sports backgrounds, and training histories. Further, the deep squatting group is a collection of competitive Weightlifters who are invariably pushing their bodies to extremes in a variety of ways to win medals. This population is not indicative of individuals that would squat for health and fitness.
• The Chi-Square test is used to determine if groups are different, but in this case the participants in the weightlifter and control groups are so different on so many levels that we cannot say these differences are due solely to deep squats.
• The p-values to indicate statistical significance are unclear as worded. Typically [p] being above 0.1 and 0.5 (as indicated in the study) would indicate no statistical difference for the comparisons.
• The author indicates standard orthopedic tests to indicate ligament status, but the reader has no idea what those tests are and is left to guess that the status is stability. But how is this stability defined/judged? Bill Starr (author of The Strongest Shall Survive: Strength Training for Football) dug deeper into this on his own and found that the test involved pressing into the ligaments (often paining the participants). There was no procedure to insure equal amounts of pressing among participants, nor any work to indicate that this pressing was a good measure of stability.
• The x-rays indicating abnormal external rotation are very difficult to read.
• Finally, a major problem lies in the author’s perspective on science. He writes: "Realizing the testing procedures used in the study were subjective tests, one has to accept the fact that an experienced tester [the author] is capable of demonstrating the evidence of stability or instability of ligaments with relative ease.” This equates to saying, the testing methods I used are subjective, so you will just have to trust me – I’m a professional. The author then goes on to say, “…one should also discount the factor of causal relationship as a chance relationship because of the medical writings related to the problem of ligament stability and instability as based on the specific movement in question.” This equates to him saying, you have to take the relationship I found as causal and not just random chance because others have written about this issue and have raised these concerns/theories. Neither of these viewpoints is scientifically sound.

Final Thoughts

Cornerstones of scientific investigation include objectivity (removal of bias), clarity of methodology and reproducibility of results. This published study is severely lacking in each of these areas and serves as an important example of how we must not take something as "fact" simply because it appears in a publication.

 

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