Effects of Diaphragmatic Manual Therapy in Chronic Low Back Pain

This study is a double-blind randomized clinical trial with two arms which aims to study the effects of diaphragmatic treatment in patients with nonspecific low back pain. Low back pain has a great importance in today's society, and it is therefore important to develop an effective treatment for this condition. People with chronic nonspecific low back pain, can present respiratory disorders and get anxiety states, affecting mainly the diaphragm muscle. Therefore, given its direct anatomic relationship, the diaphragm may be part of the development of chronic low back pain. Although clinical practice guidelines for chronic low back pain have been developed, it hasn't been explored before a physiotherapy treatment especially aimed at a diaphragmatic treatment. A double-blind randomized clinical trial with two arms will be used for this purpose, 64 patients with nonspecific low back pain referred from different hospitals of Castellón will be randomized into two groups: * Diaphragmatic intervention with osteopathic manual therapy treatment (D). * Diaphragmatic intervention with placebo treatment group (P). An osteopathic manual therapy protocol for the treatment of back pain including techniques for the diaphragm muscle will be applied to the patients in group D, in a total of 5 sessions. For patients in group P, the same protocol will be performed on the diaphragm but with placebo treatment techniques. The study focuses on the analysis of the following variables: scores on the questionnaires: * Pain: McGill Pain Questionnaire and VAS (Visual Analogical Scale ). * Fear Avoidance: (FABQ) * Disability: Oswestry Disability Index and Roland-Morris * Anxiety: HADS: (Hospital Anxiety and Depression Scale) * Catastropizing: PCS (Pain Catastropizing Scale) * Satisfaction with treatment (Escala de Satisfacción con el tratamiento) The results of these pre-intervention and post-intervention variables will be compared between the two groups in the first session, in the fourth