Effects of a brief intervention of physical exercise on somatosensory processing, lumbar lengthening and endurance of chronic low back pain patients.

INTERVENTION: Subjects will be randomly assigned to one of four study groups. The study groups are composed of three intervention groups (1, 2 and 3) and one control group (4). Intervention group (1): A single sesion of 20 minutes of moderate intensity aerobic exercise, according to 3‐4 at Borg Scale and 65‐75% of maximum heart rate, will be performed on a treadmill. Intervention group (2): A single sesion of 20 minutes of individually (one‐on‐one) lumbar strengthening exercises, supervised by an expert, will be performed. Participants will be prescribed exercises aimed at improving function of specific trunk muscles thought to control inter‐segmental movement of the spine, including transversus abdominis, multifidus, the diaphragm or pelvic floor muscles. Participants will be taught how to contract trunk muscles and progress until they will be able to maintain isolated contractions of the target muscles, each while maintaining normal respiration. Each exercise will be carry out ten times during two series and series will progress according to the patient's tolerance. Constant supervision and feedback such as palpation will be available to enhance learning of the task. Intervention group (3): A single sesion of 20 minutes of individually (one‐on‐one) lumbar flexibility exercises, supervised by an expert, will be performed according to the patient's tolerance. CONDITION: low back pain PRIMARY OUTCOME: To analyze the differences in muscle lengthening, subjects will be asked to performance the back saver sit and reach test. ; To evaluate hyperalgesia (a normally innocuous pressure of 2kg/cm2) and pain thresholds (with a maximum of 5kg/cm2) will be applied pressure on the same body locations than in primary outcome 1 (erector spinae and gluteus medius trigger points, sacral base and index finger as control body locations) with an algometer (area 1cm2). ; Subjects will be asked to indicate their pain on a VAS scale. To evaluate sensitivity, it will be applied a sensitive stimulus with Von Frey filaments on different locations (erector spinae and gluteus medius trigger points, sacral base and index finger as control body locations). Subjects will be asked to indicate the moment they feel the contact of the filament. SECONDARY OUTCOME: 6‐Minute Walk Test (6MWT) will be used to asses aerobic capacity and endurance. As a new primary outcome, to analyze the differences in muscle endurance, subjects will be asked to performance Ito test. We will also assess clinical and personal data (gender, age, height, weight, systolic and dyastolic blood preassure, pain, etc.) using a semi‐structured interview, low back disability (using Oswestry Disability Index), mood state before exercise experiences (using SEES) and during the last week (POMS), physical activity enjoyment (PACES), and behavioral regultation in exercise (BREQ‐3). INCLUSION CRITERIA: Patients with a history of mechanical and nonspecific low back pain for more than 6 weeks before the study or with intermittent low back pain who have experienced at least 3 episodes of back pain, each lasting more than a week during the year preceding the study.