I realize YANMD but I've been frustrated with my lack of progress. About two years ago I was finally struggling enough with my back pain (difficulty standing for long periods, pain when lying flat, difficulty due to pain when getting out of bed, etc) that I decided to visit a therapist and have some x-rays done. They found that I have degeneration between the L5-S1 discs. I was told that many people have this specific degeneration and that it really depends on the individual and how they react. According to the PT, some walk around completely oblivious to it while others have major difficulties. Fortunately I have progressed to somewhere between these two camps. I can perform squats but I have some difficulty with keeping my back straight while lowering. I have reduced the weight significantly in order to perform them correctly (or as best I am able). Surprising to me is that planks, even on my elbows, are extremely difficult. I'm not sure if this is a function of simply building strength or due to the degeneration. There is some pain while doing them. Given this information, I'm wondering what people do since the general recommendation is to build strength and flexibility since there is no 'cure' for this. Should I just be patient and keep at it? Are there any ideas of what I can expect for progress? Thanks for any information!
I made a quick reference here to look at nerve innervation originating below L5. Your abs should not give out due to the degradation and a loss of innervation. If the degradation was causing the problem it is much more likely that your glutes are giving out. Since they are a major stabilizing muscle this is a viable possibility. You should definitely strengthen your core (abs, back, obliques, etc.). Remember to stretch too, though. Having tight muscles that attach to the pelvis (hamstrings, piriformis, gultes, etc.) can pull the pelvis out of alignment. In turn, causing mal-positioning with your back and hips (which then affects the rest of your body).
When doing squats, maybe try using a weight-lifter's belt. While your body is out of balance you should try to assist yourself while possible. All the while, training those weaker muscles to rely less on the assisted devices.
Remember that pain is bad. If something is causing sharp pain, STOP. And as always, consult your PT or a Physician if you are unsure if you should continue to exercise.