Originally Posted by
TomC
I have a couple of comments. You are squatting on a piece of carpeting that has pictures of Pooh Bear and Tigger. This will immediately take 5 kg off of your squat. Aside from Pooh getting in your way, you can see how the carpeting is absorbing your force and shifting you around. Real lifting shoes on a solid surface will help as you can attest from being able to lift more at the university gym.
Your squats go a bit too deep for low bar, but aside from the rounding you already noticed, they are not that bad. When it gets difficult, you shift the weight on to your toes and things go down hill. Your knees don't slide forward at the bottom, but your excessive depth does seem to indicate that you need to tighten up the posterior chain a bit. Rip's constant suggestions to push your knees out and send the butt back may help.
My recommendations:
Eat more. You are underweight and putting on muscle will help everything.
Beware of Pooh and Tigger.
Squat on a hard, non-carpeted surface.
Sending your but back a little more may help keep your spine in extension.