Yup stiff leg deads
Sounds like your pretty new to them. The low back pain can be from the form your trainer chose to put you through. It is not a low back dominant exercise...it is a hip dominant exercise. Few tips
-feet are hip
width apart or further for new trainees. The hip dictates the feet not the shoulders.
- stick your butt out (this allows the hips to "hinge" properly to bear the load and keep your back neutral)
- Head follows the chest. So the head will face down as you descend. The head and eyes facing forward and up is really for those who lift extreme loads not really
proper form.
Goodluck with it