Lumbar surgery is the most common treatment for chronic disabling low back pain with degenerative disc disease. There are few elements to objectively evaluate the improvement of the motor control after surgery and the motor adaptation capacities of the patients. The impact of lumbar surgery on complexity in this painful context has never been studied. Theoretically, the restriction of mobility imposed by lumbar surgery should limit the subject's adaptive capacities (of one or more lumbar segments) and thus reduce complexity. Nevertheless, improvement in pain intensity levels could allow the patient to find better motor adaptation capacities, necessary for a positive evolution in the long-term. The aim of this study was to investigate the evolution of gait complexity in chronic low back pain patients pre- and post-surgery. If surgery improves the adaptability of walking through an antalgic benefit exceeding the induced stiffness, the complexity of walking should be superior after surgery. This is a proof-of-concept study in which the study investigators hypothesize that measuring complexity by fractal analysis during a walking task will show the increase in gait complexity induced by lumbar surgery at 3 and 6 months after surgery.