MEGAVIDEO - I'm watching it
its sideways, because mega video blows but you get the idea. any clues as to what im doing wrong?
Here are a couple of things:
1. Think about getting flat soled shoes or weightlifting shoes for squatting. Cushioning in the heels is unstable for squatting and might lead you to do #2....
2. It looks like you're transferring weight a bit from your heels to your toes as you're descending. Think about your center of gravity while you do some practice squats. Imagine the weight and pressure going straight down the middle of your foot and not towards your toes.
3. The reason you might be doing #2 is that you're not really sitting 'in between your legs' but 'over your legs.' Try breaking at the hips and shoving your ass backwards into the squat. Also push your knees outwards. You can get the feeling of this by squatting down and pushing your knees out with your elbows. If you have good flexibility, you should be able to sit in between your legs in a atg squat with back rounded indefinitely. Now try getting a neutral back angle (chest out) while in that position. That's more of the position you want to be in in the hole.
4. I notice the form got a little worse as you went from 135 to 185. You're squatting a bit higher and transferring more weight forward (and towards your knees). At 5x5 of 225 lbs, I can only imagine that your form would be even worse, which i initially suspected was the problem. This is just a guess though. We would have to see your work sets (especially the last couple) to really get a sense of how bad it will break down.
5. From what I've read and personal experience, knee strain is caused by this shifting of pressure or weight forwards towards the knees. If you go lower than parallel, then this weight is transferred to your hips (which can take much more weight). I like to imagine it like you had a broomstick rolling down your lap and thighs as you squat. If you're in ATG position, the broomstick will roll towards your lap and hips and away from your knees (the broomstick represents the pressure). At parallel and above, the broomstick or pressure will roll from your lap towards your knees. You can simulate this by getting into an ATG squat position like I outlined in #3 and then VERY slowly raising yourself to parallel and above. You will FEEL the pressure shoot from your hip to your knee. Now imagine that with 225 lbs on your back for 25 reps each time your squat.
Hope this helped. As always, check out the Squat RX series on Youtube and remember to warmup and stretch and practice.