are u using additional weight for this? Describe exactly how you're doing these, thanks.
no additional weight, without going into all of the concepts, I'll tell you practically what I'm doing. I'm moving backwards from standing upright to a full squat (ass to the grass) whilst trying to stay as far back and upright as possible.
It is a smooth, albeit slow, continuous motion, but first I'm leaning back as my arms extend forward with knees and waist unbent (I'm really moving at the ankle), then as this gets too hard I start to move back from the knee (but trying to keep the knees themselves from drifting forward), then when this gets too hard I start to let waist bend. As you get lower it gets really hard and you have to let the knees drift forward a little bit and the upper body as well.
Give it a try, unlimited leg loading is at your disposal anytime anywhere..
BTW this is so hard I can never get more than one rep.