Are Knees Coming in Really Bad?
These are a compilation 4 Instagram reels I made to address the common association between the knees coming in in various athletic positions and ACL injury risks. Are knees coming in really dangerous? Is it going to automatically lead to injuries? What does the research and modelling say?
Episode 1:
The biomechanical model of the human body as digitized is helpful because we can visualize the orientation of the body in 3D alongside the forces generated by each leg, and that’s provides a great amount of context for specific movements people are talking about.
@davidgreyrehab had done a big post talking about knees in in sports, and @jump.science had added how that only appears so from a certain perspective. I’d like to contribute a bit and help you visualize how the knees might look in from specific angles, even though the legs might be well aligned.
But at the end of the days, “knees in” is simply not a good enough descriptor. You can use context clues provided in David’s original post to best qualify the movements of the body segments.
Episode 2:
Thanks to @vitalstrengthphysiology for getting this paper on my radar. This is one step closer to investigating tissue stresses and strains during a dynamic movement, and here I break down the results of the study and how it may/may not mean what you think.
When you have a healthy cohort, it’s often really hard to gauge injury mechanisms, cause 1) they are healthy and 2) you don’t want to hurt them. You can associate tissue stresses during movements and the kinematics of the movements, however. But when you do this, you may not get what you expect, and without the full text, I am not sure if the conclusion of straight leg leading to higher acl strain is much use beyond ‘hey maybe manage your ground reaction forces somehow’.
Episode 3:
ACL Strain is not what you think? Maybe Valgus is not the culprit but the after effects? When you valgus the ACL strain actually reduces and when you straighten leg the ACL strain is actually greater?
Is knees in not the enemy all along? Does physics exist? Is something messing with our collective consciousness?
Thanks to the in vivo ACL research using the technology i talked about in my last post, we can actually figure out how the ACL behaves in movement!
Are these reserarch the downfall of slomo video based inferrences?
Max ACL strains with extended knee: https://pubmed.ncbi.nlm.nih.gov/31593...
https://pubmed.ncbi.nlm.nih.gov/33796...
https://pubmed.ncbi.nlm.nih.gov/21092...
Valgus ain't doing much:
https://pubmed.ncbi.nlm.nih.gov/22855...
https://pubmed.ncbi.nlm.nih.gov/36625...
Episode 4:
This video was made to push back against those that think knees in are bad because of link to ACL injuries. This, combined with the other modeling papers, show that ACL injuries happen likely far earlier during ground contact, and knees caving in is simply what happens after the onset of injury, as opposed to being the causal factor.
This does not say anything about knees in being good or bad for movement quality, but the injury argument that people like to bring up is 💀.
Papers here: Kissing good bye paper https://doi.org/10.1080/14763141.2021...
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