The purpose of this study is to compare the effectiveness of pain control and functional improvement in patients with degenerative spondylolisthesis treated with "lumbar stabilization exercises" vs "flexor exercises (williams exercises)"

This study is a randomized controlled trial in patients with the diagnosis of degenerative spondylolisthesis.

To date, it is known that lumbar stabilization exercises are an effective treatment option in controlling pain and improving function in patients with degenerative spondylolisthesis based on previous studies, but it is not known if is this a better treatment that another exercises routine for chronic LBP (Low Back Pain).

The purpose is to compare the effectiveness on pain control and functional improvement of "lumbar stabilization exercises" vs "flexor exercises (williams exercises)".

All clinical evaluations are performed by a single physician who is blinded to the exercises, and include a full medical history, physical examination, and x-ray measurement.

After initial evaluation, patients are given a sealed envelope containing the treatment (by simple randomization assigned by the investigator). The envelope is opened by the physical therapist which schedules a monthly session and verify the correct execution of each exercise. Each patient receives a sheet with instructions of the exercises to continue daily at home.

Scales to assess pain and function will be recorded at baseline, 4 weeks, 3 months and at 6 months to complete the follow up.

Inclusion Criteria:

• Degenerative spondylolisthesis at L4-L5 and chronic LBP with or without radicular pain
• Attending the Spinal Rehabilitation Service of the National Institute for Rehabilitation (Mexico City).
• Without previous treatment
• Agree to participate through informed consent.

Exclusion Criteria:

• History of lumbar surgery,
• Rheumatic diseases: Rheumatoid Arthritis, Lupus Erythematosus Systemic, Fibromyalgia, etc.
• Cauda equine symptoms,
• Ischemic heart disease
• Diabetic polyneuropathy
• Illiterate