Yes you may!
This is the story we have been told for ages:
“Don't let your knees go in during a squat!”
“You will injure yourself if your knees go in during a squat!”
Well it turns out this is just not true. Humans are incredibly resilient and able to move in many different ways. What determines injury is not form, it's load. This means that if you follow graded exercise, increasing your load little by little (not more than 10% increase per week), and you make sure you pull up fine the day after a workout, you will not injure yourself no matter what technique you are practicing.
It was previously thought that knees going in during jumping would cause ACL injury. But it turns out this is also not true. This Systematic Review from 2020 disproves that theory (1).
The world champion power lifter Lya Bavoli uses a "knees in" technique during her record breaking squat, and her knees are doing just fine! Check her out being awesome here.
So why do some peoples' knees go inwards during a squat anyway? There are some theories (nothing official though)...
First of all, all humans are different. We have different shaped pelvises, our femoral necks are at different angles, different femur to torso lengths, different knees, ankles, etc. Get the picture? So if our structures are all different, what exactly makes us think our squats should look the same? Some people will squat better with a wider stance, others with a more narrow stance. Some will find the best results with knees out, others with knees in.
That doesn't mean one way is better or more correct than another. It just means that for each person there will be an optimal way to squat (to be able to produce more load with less effort = efficiency). We most definitely can't say that way will be the same for the entire population.
Weird that we thought that for so long!
Another theory I like is that the knees might go in on the way out of a squat for some lifters as a way to actually produce more force. This is because when the knees go in, the illiotibial band (IT Band) gets put on stretch (like a rubber band), and when the knees come back out again, that stored energy acts exactly like a rubber band giving us that extra boost out of the squat. For some people (not everyone) this could be an amazing way the body is solving the problem of how to produce more force with less effort.
If you're interested in hearing a more in-depth explanation, check out this Pilates Elephants podcast!
Until next time, I wish you happy squatting!