Direction Matters: A Crossover Study on Motor Adaptations to Movement-Evoked Pain Induced in the Lumbar Region

Background

People with chronic low back pain (LBP) often experience pain evoked by movement (movement-evoked pain [MEP]). Although pain changes how people move, it remains unclear whether motor adaptations to LBP are specific to the pain-provocative movement. This crossover experimental study aimed to understand whether pain modulated by movement in different directions induces distinct motor adaptations, and if these adaptations are consistent with a purposeful strategy to minimise pain.

Methods

Thirty healthy adults performed a repetitive box lifting task in two experimental sessions. Experimental pain was induced in the lumbosacral region using nociceptive electrical stimulation, with intensity modulated proportionally to either lumbar flexion or extension. Within-subject changes in kinematics and centre of pressure were assessed both during and post-pain.

Results

During both sessions and over time, participants reduced their lumbar movement in the pain-provocative direction (p < 0.01), but not in the non-pain-provoking direction (p > 0.078). The reduction in lumbar flexion was strongly associated with perceived pain intensity (p < 0.001) and persisted beyond pain resolution (p < 0.001). Pain during lumbar flexion also induced other acute motor adaptations, including reduced elbow flexion (p = 0.027) and an anterior shift of the centre of pressure (p < 0.001).

Conclusions

This study revealed that the direction of the pain-provocative movement is a determinant factor in motor adaptations to pain, with clinical implications in developing personalised, movement-based interventions for LBP. Further, motor adaptations were not simply a generic acute response to pain but evolved to minimise pain, supporting the proposal that MEP is a motivational stimulus for adaptive behaviour driven by learning.

Significance Statement

This study shows that motor adaptations to MEP are specific to the direction of pain-provocative movement, evolve over time and represent a purposeful strategy to reduce pain. These findings highlight the reciprocal interactions between pain and movement, supporting the rationale for assessing motor strategies in people with movement-evoked LBP.