Influence of Verbal Suggestion on the Therapeutic Effect of the Joint Manipulation

The aim of the study is to evaluate the influence of verbal suggestion on the therapeutic effect of the joint manipulation of the lumbar spine in patients with chronic non-specific low back pain in relation to the pain level, stress, disability, function, sleepiness, tissue temperature and selected blood biochemical markers. The study participants will be randomly assigned (sealed allocation envelopes) to the following groups: * Group A (test intervention + placebo communication) * Group B (test intervention + nocebo communication) * Group C (test intervention + neutral communication) The study will mainly consist of the three stages, i.e. before the intervention, immediately after the intervention and 24 hours later.