Effects of mental simulation of different movements on postural control

Abstract

Introduction: The motor imagery (MI) is the act of mentally simulate an action without actually executing it. The MI can induce a modulation in the postural sways during standing. Nevertheless, there is no evidence of task-specificity change in postural sway during MI. Objective: Investigate whether the modulation of postural control during the MI depends on the characteristics of the imagined movement. Methods: Participants (n=23) were instructed to perform and imagine, for 45 seconds, the following tasks over a force plate: (1) lateral reaching (LR) movement whit right upper limb; (2) bilateral plantar flexion (PF) motion and (3) forward reaching (FR) movement whit right upper limb. As a control condition, subjects were asked to stand quietly with the eyes closed (EC). After each task participants reported the vividness of the imagined sensation, the fear of falling, and the number of movements executed and imagined. During the IM tasks the feet center of pressure displacement (SD, standard deviation; MV, mean velocity) and the amplitude of the electromyographic (EMG) activity of task related muscles (middle deltoid, lateral gastrocnemius and anterior deltoid) were analyzed. The statistical analyses for each parameter were employed repeated measures one-way ANOVA (conditions as factor) and Bonferroni post-hoc test. Results: The MI of PF promotes higher SD in the anterior-posterior (AP) axis compared to the conditions of EC (p=0.01) and MI of FR (p=0.04). The MV in the AP axis was higher in all MI tasks compared with EC condition (p<0.001). Furthermore, there were differences between the MI of PF and the MI of LR (p=0.02). The SD in the medial-lateral (ML) axis showed a significant difference between the MI of LR and the EC condition (p=0.02). The MV on the ML axis was higher in all the MI tasks, compared with the EC condition (p<0.001), and between MI tasks of FR and LR (p=0.03). There was no difference in the vividness of the MI and in the fear of falling between tasks, indicating that postural modulations were not induced by these variables. In addition, there was no difference (Wilcoxon test) in the number of movements executed and imagined, indicating that the MI was properly performed. Finally, there was no difference in the EMG amplitude measures, indicating no additional muscle contraction during simulation. Conclusion: The MI modulates postural control depending on the characteristics of the imagined task.