Low back pain thathurts with standing 15 minutes or more and then muscles tighten and only bending relievesat all?

Spinal stenosis: Reduced tolerance to standing and/or walking may be an indication that you could have spinal stenosis (narrowing of your spinal canal). Like you, patients with stenosis typically have improvement of their symptoms when they bend forward. This is called a positive cart sign because leaning forward against a shopping cart can help open up the canal and can, therefore, lead to symptom improvement.

Facet joint pain: Classic case of lumbar facet joint pain usually caused by arthritis. Treatment includes physical therapy, chiropractic, and facet injections for severe episodes. Surgery almost never required.