Hey George, just to clarify: do you mean you’re losing the lumbar curve in your deep squat? In my athletes, the more naturally gifted athletically, and stronger, the harder it is to get them to keep everything engaged down low in the squat, because its easier to relax down there. Are you screwing your feet into the ground before you squat, and continuing to do that as you squat? Most people’s range of motion in the hips will stop their squat before they lose the lumbar curve, if they’re keeping everything engaged. When you run out of range of motion without getting “loose”, then that’s the bottom of your squat. Let me know if this makes sense, or if you pinpoint a weakness.
Hal