New insight into motor adaptation to pain revealed by a combination of modelling and empirical approaches

Abstract

Background: Movement changes in pain. Unlike the somewhatstereotypical response of limb muscles to pain, trunk muscle responses arehighly variable when challenged by pain in that region. This has led manyto question the existence of a common underlying theory to explain theadaptation. Here, we tested the hypotheses that (1) adaptation in muscleactivation in acute pain leads to enhanced spine stability, despite variationin the pattern of muscle activation changes; and (2) individuals would usea similar ‘signature’ pattern for tasks with different mechanical demands.Methods: In 17 healthy individuals, electromyography recordings weremade from a broad array of anterior and posterior trunk muscles whileparticipants moved slowly between trunk flexion and extension with andwithout experimentally induced back pain. Hypotheses were tested byestimating spine stability (Stability Index) with an electromyography-driven spine model and analysis of individual and overall (net) adapta-tions in muscle activation.Results: The Stability Index (P < 0.017) and net muscle activity(P < 0.021) increased during pain, although no two individuals used thesame pattern of adaptation in muscle activity. For most, the adaptation wassimilar between movement directions despite opposite movementdemands.Conclusions: These data provide the first empirical confirmation that, inmost individuals, acute back pain leads to increased spinal stability andthat the pattern of muscle activity is not stereotypical, but instead involvesan individual-specific response to pain. This adaptation is likely to provideshort-term benefit to enhance spinal protection, but could have long-termconsequences for spinal health.