@kennycro@@aol.com, I question what seems like the underlying assumption, that we can measure the strength of every or any muscle in a meaningful way.
Measuring Muscle Activation
The research article provides the method that employed to measure Lumbar strength. Provide me your email and I'll send it to you for your analysis.
It is mentioned in the article under...
Testing:
Isolated Lumbar Extension Strength Testing. Participants were seated in the ILEX device (Lumbar Extension Machine; MedX Corporation, Ocala, FL, USA). The ILEX device uses restraints to limit unwanted pelvic involvement in an upright position with their thighs at an angle of 15 degrees to the seat in the testing (Figure 1), in addition to a counterweight to neutralize the effects of gravitational forces on the head, torso, and upper extremities. ...
it's not something that, at least for this competing deadlifter with a history of a bad back,
Reiteration of Initial Post
As I stated, "...if someone has back issues, they might not be something to consider. ... And as the saying goes, "If it hurts, don't do it".
Walking
I believe that you do a lot of walking, correct? As I noted it the post above, for individual with lower back issues, walking is a recommended exercise.
Sled Pulls
THE USE OF HEAVY SLED DRAGGING TO INCREASE LOWER BODY STRENGTH AND SPEED IN A FOOTBALL PLAYER WITH LUMBAR ISSUES
This research article demonstrated this type of Resistance Walking for athletes with lower back issues was effective for increasing strength.
McLaughlin's Bio-Mechanic Deadlift Research
I have posted information on McLaughlin's Bio-Mechanic Deadlift Research on this site.
His research demonstrated that with a Conventional Deadlift, the majority break the weight off the floor by initiating the drive with the lower back, with some secondary assistance from the legs.
As McLaughlin and even Contreras have noted, "Leg Pressing" the weight off the floor or the recommendation of "Push the Floor away from you" is counter productive for moving more weight.
Anna performs her Conventional Deadlifts in the same way; more leg drive that back. One of the exercise that she posted that helped her was Halting Deadlifts.
Based on Anna's leg strength, I suspect that she would pull more going Sumo.
Your Deadlift
I realize that due to your back issues, you use leg drive to break the weight off the floor. That is probably one of the reasons that it come off the floor so slow and your pull is stronger at the top.
With your back issues, I understand why you Deadlift this way.
Sumo Deadlift
Since you have back issues and employ leg drive to break the weight off the floor, I have often wondered why you don't go Sumo. Secondly (as you know), there is less stress on the lower back.
I am sure you have tried Sumo. I am just curious as to how it worked for you.
Squat Stance Deadlift
I am sure you have tried this one. How did it work for you?