The Six-Minute Walking Test (6MWT) as a Measure of Functional Impairment in Lumbar Degenerate Disc Disease.

Inclusion Criteria:

   - Patient scheduled for spine surgery with one of the following diagnosis (1) lumbar
   disc herniation (LDH), (2) lumbar spinal stenosis lumbar (LSS) or lumbar DDD with or
   without instability requiring lumbar fusion (transforaminal lumbar interbody fusion,
   posterior lumbar interbody fusion, or extreme lateral interbody fusion)

   - Male and Female subjects ≥ 18 years

   - Written informed consent

Exclusion Criteria:

   - Pregnancy

   - Inability to walk (extreme pain or severe neurological deficits)

   - Severe Chronic Obstructive Lung Disease (COPD) corresponding to ≥ Gold III

   - Severe heart failure corresponding to ≥ New York Heart Association (NYHA) III

   - Lung cancer and diffuse parenchymal lung disease

   - Other medical reasons interfering with the patient's ability to walk and perform the
   6MWT (e.g., osteoarthritis disease of the lower extremities, Parkinson's disease,
   heart failure, hip or knee prosthesis etc.)

   - Unavailability for follow up and/or inability to complete assessment (planning to
   move, no smartphone, etc.).