The influence of expectation on spinal manipulation induced hypoalgesia: an experimental study in normal subjects.

Bialosky JE, Bishop MD, Robinson ME, Barabas JA, George SZ

The purpose of this study was to determine the effect of subject expectation on hypoalgesia associated with SMT. Sixty healthy subjects agreed to participate and underwent quantitative sensory testing (QST) to their leg and low back. Next, participants were randomly assigned to receive a positive, negative, or neutral expectation instructional set regarding the effects of a specific SMT technique on pain perception. Following the instructional set, all subjects received SMT and underwent repeat QST. The results showed no interaction between group assignment and pain response was present in the lower extremity following SMT, however, a main effect for hypoalgesia was present. A significant interaction was present between change in pain perception and group assignment in the low back with participants receiving a negative expectation instructional set demonstrating significant hyperalgesia.

The current study replicates prior findings of c- fiber mediated hypoalgesia in the lower extremity following SMT and this occurred regardless of expectation. A significant increase in pain perception occurred following SMT in the low back of participants receiving negative expectation suggesting a potential influence of expectation on SMT induced hypoalgesia in the body area to which the expectation is directed.

BMC Musculoskelet Disord. 2008, 9, 19

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