This observational study aims to investigate the internal responsiveness and external responsiveness of the Bridge Tests (supine bridge test, prone bridge test, and side bridge test) in relation to pain and disability, in subjects with subacute and chronic non-specific low back pain submitted to a physical therapy program.

Time 0 (first session of the physical therapy treatment program)

The physical therapist will explain to each patient the purpose of the study and request informed consent and data processing consent. In the informed consent form will be specified that the study will concern some diagnostic tests and the study protocol will not influence the physical therapy treatment strategy in any way. Only those who give their consent will be included in the study and will fill in a booklet containing:

• socio-demographical, anthropometric and pain data;
• the Italian version of the Oswestry Disability Index (ODI-I);
• the Italian version of the 0-100 Numerical Rating Scale (NRS). Once completed, the questionnaires will be placed in a sealed envelope and delivered to the examiner.

The physical therapist will perform the following tests, without being aware of the results collected during the initial clinical evaluation and will record the tests results on a pre-printed sheet, which will then be inserted in the same envelope as well.

The tests performed are (in order of execution):

• Aberrant Movements (AM) Test,
• Active Straight Leg Raise (ASLR) Test,
• Supine Bridge Test (SuBT),
• Right Side Bridge Test (RBT),
• Left Side Bridge Test (LBT),
• Prone Bridge Test (PrBT),
• Passive Lumbar Extension (PLE) Test,
• Prone Instability Test (PIT).

The envelope containing the patient's data and the results of the tests will be sent to an independent subject, who will take care of the data collection and their insertion into the electronic database, assigning to each patient a numerical code as the only identification element.

The patients will be submitted to a physical therapy treatment for eight 30-minutes sessions, once a week.

Time 1 (at the end of the last session of the physical therapy treatment)

Those who have completed the physical therapy treatment will receive a final booklet containing the Italian version of the Oswestry Disability Index (ODI-I), the Numerical Rating Scale (NRS) and the Global Perceived Effect (GPE) Questionnaire. Once completed, these questionnaires will be placed in a sealed envelope and delivered to the examiner.

Without being aware of the outcome of the questionnaires contained in the final booklet, the same tests will be repeated:

• Aberrant Movements (AM) Test,
• Active Straight Leg Raise (ASLR) Test,
• Supine Bridge Test (SuBT),
• Right Side Bridge Test (RBT),
• Left Side Bridge Test (LBT),
• Prone Bridge Test (PrBT),
• Passive Lumbar Extension (PLE) Test,
• Prone Instability Test (PIT).

Test results will be recorded on a pre-printed sheet, which will then be inserted in the same envelope and send to the independent subject who is responsible for data collection.

Inclusion Criteria:

• Non-specific subacute or chronic low back pain (low back pain from 1 month or more, not related to specific pathologies);
• Low back pain, with or without irradiation to the lower limb, noted as ≥2 on a scale of 0-10;
• Good comprehension of written and spoken Italian Language;
• Informed consent.

Exclusion Criteria:

• Acute low back pain;
• Specific causes of low back pain (truma, herniated disc, vertebral deformity, fractures, dislocations);
• Central or peripheral neurologic signs;
• Systemic pathologies;
• Rheumatic disorders;
• Neuromuscular pathologies;
• Tumors;
• Cognitive deficits;
• Surgical interventions in the last six months prior to the study;
• Osteoporosis.

All outpatients entering the conservative physical therapy treatment for subacute or chronic non-specific low back pain in a Occupational Medicine Unit are considered eligible.