Journal of Pain Research (Feb 2021)
Promising Effect of Visually-Assisted Motor Imagery Against Arthrogenic Muscle Inhibition – A Human Experimental Pain Study
Abstract
Shota Oda,1 Masashi Izumi,1,2 Shogo Takaya,1,2 Nobuaki Tadokoro,2 Koji Aso,2 Kristian Kjær Petersen,3 Masahiko Ikeuchi1,2 1Department of Rehabilitation Center, Kochi Medical School Hospital, Nankoku, Kochi, Japan; 2Department of Orthopedic Surgery, Kochi University, Nankoku, Kochi, Japan; 3Center for Neuroplasticity and Pain (CNAP), Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, DenmarkCorrespondence: Masashi IzumiDepartment of Orthopedic Surgery, Kochi University, Oko-Cho Kohasu, Nankoku, Kochi, Japan, 783-8505 Tel +81-88-880-2386Fax +81-88-880-2388Email [email protected]: Clinically, arthrogenic muscle inhibition (AMI) has a negative impact on functional recovery in musculoskeletal disorders. One possible technique to relieve AMI is motor imagery, which is widely used in neurological rehabilitation to enhance motor neuron excitability. The purpose of this study was to verify the efficacy of visually-assisted motor imagery against AMI using a human experimental pain model.Methods: Ten healthy volunteers were included. Experimental ankle pain was induced by hypertonic saline infusion into unilateral Kager’s fat pad. Isotonic saline was used as control. Subjects were instructed to imagine while watching a movie in which repetitive motion of their own ankle or fingers was shown. H-reflex normalized by the motor response (H/M ratio) on soleus muscle, maximal voluntary contraction (MVC) force of ankle flexion, and contractile activities of the calf muscles during MVC were recorded at baseline, pre-intervention, post-intervention, and 10 minutes after the pain had subsided.Results: Hypertonic saline produced continuous and constant peri-ankle pain (VAS peak [median]= 6.7 [2.1– 8.4] cm) compared to isotonic saline (0 [0– 0.8] cm). In response to pain, there were significant decreases in the H/M ratio, MVC and contractile activities (P< 0.01), all of which were successfully reversed after the ankle motion imagery. In contrast, no significant changes were observed with the finger motion imagery.Conclusion: Visually-assisted motor imagery improved the pain-induced AMI. Motor imagery of the painful joint itself would efficiently work for relieving AMI. This investigation possibly shows the potential of a novel and versatile approach against AMI for patients with musculoskeletal pain.Keywords: arthrogenic muscle inhibition, experimental ankle pain model, visually-assisted motor imagery
