Some authors claim that patients with musculoskeletal pain tend to underestimate their levels of muscle tension. The results of studies find evidences of the deficits in the perception of muscular tension in patients with chronic pain, being this the pathogenic factor in some musculoskeletal alterations. These studies show that patients with chronic pain can not identify their muscle tension and suggest that this contributes to maintaining pain. Thus, positive results have been found with relaxation and electromyographic biofeedback in patients with chronic pain. If these symptoms are due to excessive stress, patients should be able to benefit from regulation of muscle activity through BFB-EMG, thus learning to regulate the physiological variable. The study will be carried out in the electrotherapy laboratory of the Health Sciences Building of the University of Almeria. Initially, the sample will be chosen and the informed consent of the subjects will be obtained. Before the start of treatment, a baseline assessment of the dependent variables will be performed. Subsequently subjects will undergo three sessions of manipulative therapy over 12 weeks (one session per week). After the therapeutic intervention, a new determination of the dependent variables will be performed.