Lumbar fusion has been widely used for spinal disorders when conservative treatment has failed. However, a number of studies have reported that the rate of re-operation is high for lumbar fusion surgery. Swelling, atrophy or fat infiltration of the paraspinal muscles at the surgery site can cause weakness and pain. After fusion, the range of motion is constrained at the fused spine and might facilitate compensative movement of the adjacent levels and increase degeneration rate of the spine.

Evidence has shown that core muscles play an important role to stabilize and support the spine. Whether core stability exercise can enhance spinal stability after lumbar fusion surgery remains unclear. Therefore, the overall goal of this proposed research is to investigate how core muscles affect outcomes after lumbar spinal fusion. The investigators will explore this issue hierarchically and systematically in 3-year duration.

Inclusion Criteria:

1. ages between 20 and 85 years,
2. back pain and/or sciatica exceeding 12 weeks for which conservative treatment had failed to improve,
3. a primary diagnosis of spinal stenosis, spondylosis, degenerative or isthmic spondylolisthesis or degenerative disc disease, and
4. the patient selected for lumbar surgery

Exclusion Criteria:

1. mechanical back pain due to posture changes and cannot maintain an upright posture over 30 minutes;
2. segmental instability that includes isthmic spondylolisthesis, degenerative spondylolisthesis over 0.4 cm;
3. intervertebral angle reversal on dynamic radiographs; and
4. previous lumbar fusion, rheumatoid arthritis, and ankylosing spondylitis.

All subjects will be recruited from the National Taiwan University Hospital and Far Eastern Memorial Hospital. The study is approved by the Institutional Medical Research Ethics Committees in both National Taiwan University Hospital and Far Eastern Memorial Hospital. Our neurological surgeon will response for subject screening and medical diagnose. According to the power analysis, fifty subjects will be enrolled in this study. The eligible subject will be given the subjects informed consent and sign it before the enrollment.