There are several cases of chronic low back pain I've seen over the years where I had to use isometric resisted extension to restore lumbar extension in standing. I noticed the longer some had pain, the less they were able to resist this motion. Even strong/athletic people were VERY weak in lumbar extension. This didn't change when their pain improved. I started looking into lumbar extension testing and as a general exercise for chronic low back pain. The research isn't very recent but there is some to suggest that it could help. Just another tool to try if your normal programs aren't working. Lmk what you think!
References
Steele J, Bruce-Low S, Smith D. A review of the clinical value of isolated lumbar extension resistance training for chronic low back pain. PM R. 2015 Feb;7(2):169-87.
Lee KW, Hwang JH, Bang HJ. Isometric evaluation of the lumbar extensors in chronic low back pain. J Korean Acad Rehabil Med. 1997;21(1):1-7.
Roussel NA, Truijen S, De Kerf I, Lambeets D, Nijs J, Stassijns G. Reliability of the assessment of lumbar range of motion and maximal isometric strength in patients with chronic low back pain. Arch Phys Med Rehabil. 2008 Apr;89(4):788-91.
Renkawitz T, Boluki D, Grifka J. The association of low back pain, neuromuscular imbalance, and trunk extension strength in athletes. Spine J. 2006 Nov-Dec;6(6):673-83.
Smith D, Bissell G, Bruce-Low S, Wakefield C. The effect of lumbar extension training with and without pelvic stabilization on lumbar strength and low back pain. J Back Musculoskelet Rehabil. 2011;24(4):241-9.
O'Sullivan K, Smith A, Beales DJ, Straker L. The relationship between balance performance, lumbar extension strength, trunk extension endurance, and pain in participants with chronic low back pain, and those without. Clin Biomech. 2018 Mar;53:22-30.