The objective of this study is to investigate the comparative benefit of thrust and non-thrust manipulation on a population of patients with low back pain. The investigators hypothesize that there will be no difference in 4 week outcomes or greater, between the two groups.

Thrust manipulation is considered traditional spinal manipulation. Nonthrust manipulation is considered mobilization. The mobilization will be used in a similar manner as in clinical practice and this differs from past studies.

Inclusion Criteria:

• Patients, age 18 and older, with mechanically producible low back pain, who attend care at a physical therapy outpatient setting, will be screened for eligibility for the study.
• For patients to meet inclusion requirements, they had to display a within session change in pain and/or range of motion during the assessment phase of the clinical examination. In other words, as the clinician performed their assessment and applied a passive accessory assessment technique, the pain and/or range of motion improved during that session, which suggests a favorable outcome using a comparable treatment technique. This is hallmark clinical finding in the patient response model and has been proposed as both a predictor of a positive outcome and as a prognostic variable toward long-term improvements in impairments.

Exclusion Criteria:

• The presence of any red flags (i.e., tumor, metabolic diseases, RA, osteoporosis, prolonged history of steroid use, etc.)
• Signs consistent with nerve root compression (reproduction of low back or leg pain with straight leg raise at less than 45°
• Muscle weakness involving a major muscle group of the lower extremity,
• Diminished lower extremity muscle stretch reflex
• Diminished or absent sensation to pinprick in any lower extremity dermatome)
• Other exclusion criteria included prior surgery to the lumbar spine and current pregnancy