Background: There are reports about the importance of pain-related fear in the transition from acute to chronic musculoskeletal pain. However, there are no studies about expectancy and impaired fear inhibitory learning in the understanding of the transition from acute to chronic Low Back Pain (LBP). These variables can be obtained by classical conditioned experiment. Instead of the great number of cross-sectional studies investigating classical conditioned responses in healthy volunteers there are no studies using longitudinal designs assessing these aspects. Additionally, there is the need to understand the role of different factors on pain and disability and its influences on response to treatment. Substantial research efforts are focused on elucidating prognostic and predictive factors especially in chronic and disabling disorders such as LBP. Objectives: Study 1- to identify the predictive value of conditioned fear and pain responses and expectations of recovery to the persistence of LBP in acute/subacute patients, after one-month follow-up and Study 2 - to identify the prognostic value of likelihood of pain and fear conditioning related to movement (pain and fear expectations) for persistence of LBP after a brief Pain Neurophysiology Education (PNE) intervention at 1- and 3-month follow-up. Methods: Study 1: One hundred fifty (n=150) participants with acute LBP and 30 asymptomatic volunteers will be invited to attend the Research Laboratory to be submitted to a battery of questionnaires and a brief clinical assessment before the psychophysiological tests (classical conditioning experiment). After the one-month period, participants with persistence of LBP (n=30) and recovered (n=30) will be invited to the second phase of the study 1 and all assessments will be applied again. Using visual observation of pictures depicting low back movements as conditioning paradigm, we will compare startle electromyogram responses, shock expectancy ratings and pain-related fear during acquisition and generalizations phases of conditioning experiment. For Study 2, four hundred patients with acute LBP will be recruited online (social media). The volunteers will be assessed through clinical, psychosocial questionnaires and an experiment on likelihood of conditioned pain and fear related to low back movements. After this initial evaluation, they will be submitted to an early and brief session of PNE. All volunteers will be re-assessed after a one- and three-month follow-up period.
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