Do trunk-based left/right judgment tasks elicit motor imagery?

Background: Left/right judgment tasks (LRJTs) are used in the management of chronic pain. This use is predicated on their ability to elicit the simulation of movements (i.e. motor imagery), including those where the execution of the same movements induces pain. While established for limb-based LRJTs, the ability of trunk-based LRJTs to elicit motor imagery of trunk movements has not been demonstrated. Objective: To establish whether data from a trunk-based LRJT are indicative of motor imagery being elicited for the specific lateralised trunk postures presented. Design: Cross-sectional repeated measures (within-subject experiment). Methods: Twenty-nine unimpaired and pain-free participants completed a trunk-based LRJT typical of those used in practice. Accordingly, left/right judgements were made to images depicting a human figure with its trunk rotated or side-flexed to the left or right. The extent (amplitude) of this movement was manipulated (small, medium, large). The whole figure was also oriented to different degrees (0 degrees, 45 degrees, 90 degrees, 135 degrees, 180 degrees) and along different axes (sagittal, axial, coronal). Results: Accuracy was higher and response times (RTs) faster (p < 0.001 for both) when lateralised trunk movements depicted had a larger amplitude, contrary to predictions if motor imagery was elicited. Differences in accuracy and RTs depending on the orientation of the whole figure were consistent with previous studies. Discussion: Data were not consistent with motor imagery of lateralised trunk movements being elicited by the trunk-based LRJT. The study presented here questions the value of trunk-based LRJTs in clinical practice.