Conditioned Pain Modulation in Chronic Neck Pain Patients

1. Chronic neck pain subjects Inclusion criteria: * Age 21-80 years old. * People must have experienced neck pain for at least 3 months and have reported a minimal pain level of 30 (pain threshold) on the 0-100 pain numerical rating scale (NRS) in the last 7 days. Exclusion Criteria: * Age under 21 or over 80. * Patients were excluded if they had taken pain medications on the day of the assessment or if they had serious spinal pathologies, such as fractures, tumors or inflammatory diseases, such as ankylosing spondylitis, nerve root compromise confirmed by clinical neurological tests or severe cardiorespiratory diseases. * Those who were pregnant, patients with cancer and those with a cardiac pacemaker were also excluded. 2. Healthy volunteers Inclusion criteria: * Age 21-80 years old. * These participants must not have presented episodes of low back pain for more than 7 days in the last 12 months. Exclusion Criteria: * Age below 21 or over 80 years old. * These participants have presented episodes of low back pain for more than 7 days in the last 12 months.