When I do heavy Good Mornings, Stiff-leg dead-lifts, DL (and squats with forward lean) my hips move about an inch or two to the right. This concerns me as I had a lower-back injury many years ago and I suspect that it may have been related to this. Other than the involuntary lateral shifting of the hips, I use proper form when performing my exercises.
I had tried doing unilateral exercises such as step-ups, leg-curls, etc suspecting it may be the result of a strength imbalance in the Hams or Quads (my left leg is slightly stronger + bigger than the right) but the problem persisted.
One solution I have found is using a wide-stance when performing the above mentioned movements. This tends to minimize any lateral movement in the hips. However, if a strength or flexibility imbalance exists this solution would only mask the problem IMO. I suspect that even when using a wide stance, although there would be no or minimal shifting of the hips, that there would be an uneven strain on the lower back (which is what I believe caused my lower-back injury).
BTW, my left erector (lower-back) muscle is much more developed than the right one validating the idea that it is being stressed more in training.
My strength is increasing and I am worried that I may injure myself again. Any suggestions would be very much appreciated.