Lumbar Disc Herniation: This condition is commonly associated with symptoms that worsen with flexion and prolonged sitting due to increased pressure on the lumbar discs, leading to herniation and potential nerve root compression.

Lumbar Spondylosis: Degenerative changes in the lumbar spine can cause pain and stiffness, especially with activities that increase lumbar flexion, such as sitting for long periods.
Spondylolisthesis: This condition, where one vertebra slips forward over the one below it, can cause back pain that worsens with flexion and prolonged sitting due to increased stress on the affected segment.
Lumbar Spinal Stenosis: Narrowing of the lumbar spinal canal can cause pain, numbness, and weakness in the legs, symptoms of which can be exacerbated by flexion and prolonged sitting.

Cauda Equina Syndrome: A serious condition caused by compression of the cauda equina (nerve roots in the lower spine), which can present with severe back pain, sciatica, and neurological deficits. It is a medical emergency requiring prompt intervention.
Spinal Infection (e.g., Discitis, Osteomyelitis): Infections of the spine can cause severe back pain and neurological symptoms, which may worsen with movement or position changes, including flexion and prolonged sitting.
Spinal Tumor: Tumors in the spine can cause back pain and neurological symptoms that may worsen with certain positions or activities, including flexion and prolonged sitting.

Scheuermann's Disease: A rare condition characterized by kyphosis (forward rounding) of the upper back, which can cause back pain and stiffness, potentially worsening with flexion and prolonged sitting.
Ankylosing Spondylitis: A form of arthritis that primarily affects the spine, although it can also affect other joints. Symptoms include pain and stiffness in the back, which may worsen with certain positions or activities.