Effects of Hidden Conditioning and Positive Expectations on Pain Intensity Following Spinal Manipulative Therapy: A Three‐Arm Randomized Controlled Trial

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Abstract
Background: Conditioning and positive expectations are potential mechanisms for pain relief. However, there is a gap in the literature on the isolated or combined impact of these factors for decreasing pain intensity. Methods: This study investigated whether a hidden conditioning procedure with a hidden lowering of the thermal noxious stimulus during a conditioning session combined with positive expectation would result in greater low back pain intensity reduction compared to positive and neutral expectations alone. All groups participating in the study received six sessions of spinal manipulative therapy (SMT). Patients ( n = 264) with nonspecific chronic low back pain (CLBP), aged between 18 and 65 years, were randomly allocated to three groups: hidden conditioning with positive expectations (C‐PEG), positive expectations alone (PEG), or neutral expectations alone (NEUG). Participants were submitted to a conditioning test pre‐ and post‐first session of SMT, where heat pain stimuli were surreptitiously lowered only in the C‐PEG group. The primary outcomes were low back pain intensity and global perceived effect (GPE) of improvement assessed post‐first SMT session and at 6‐week (primary endpoint) and 3‐month follow‐ups. Linear mixed‐effects models were used to assess group and time effects. Results: No significant difference was found between the three groups at any of the follow‐ups for pain intensity or GPE. Positive expectations (pre‐treatment) and psychosocial variables partially mediated the relationship between baseline low back pain and disability outcomes. All groups showed a within‐group reduction in low back pain and disability at follow‐ups. Significance Statement: Conditioning and positive expectation with SMT did not improve pain intensity or GPE outcomes for participants with low back pain, when compared to positive or neutral expectations alone. These findings suggest that patients did not generalize learned associations during conditioning to low back pain intensity outcome. Regardless of treatment assignment, positive expectations and psychosocial factors played a mediating role in pain intensity, GPE, and disability outcomes. Trial Registration: ClinicalTrials.gov identifier: NCT05202704
Funding Information
  • Fundação de Amparo à Pesquisa do Estado de São Paulo (2019/22924‐6)
  • Fundação de Amparo à Pesquisa do Estado de São Paulo (2019/23356‐1)
  • Conselho Nacional de Desenvolvimento Científico e Tecnológico (302223/2022‐3)

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