Effects of Tongue Training Tasks on Intramuscular Activity Distribution: Evaluation Using Muscle Functional Magnetic Resonance Imaging

ABSTRACT Background From the perspective of site specificity, inducing muscle activity across a large area of the tongue through diversified tongue resistance training (TRT) may be an effective approach to improve tongue pressure (TP) and function. However, the distribution of muscle activity within the tongue during different TRT exercises remains unclear. Objectives To examine the hypothesis that muscle activity distribution within the tongue varies with TRT direction using muscle functional magnetic resonance imaging (mfMRI), and to clarify the relationship between these distributions and functional outcomes. Methods Twenty young volunteers were randomly assigned to either an elevation or a lateral 4 week TRT group. We performed mfMRI before (at rest) and immediately following each training task, before and after 4 weeks of TRT, and we measured maximal elevation, lateral TP, and oral diadochokinesis (ODK). A linear mixed‐effects model was used to analyse the functional outcomes. Results After TRT, mfMRI revealed that elevation exercise activated the anterior tongue, including the origin of the genioglossus. Conversely, lateral exercise induced significant activity across a wider area extending to the tongue root. Post‐training maximal elevation TP and overall ODK values were significantly higher in the elevation training group. No significant differences between groups were observed in post‐training lateral TP. Conclusions TRT direction changes the pattern of muscle activity in the tongue. This finding reveals qualitative aspects of TRT that cannot be evaluated by post‐training TP alone, offering a new perspective for designing more effective rehabilitation programs. Trial Registration ClinicalTrials.gov identifier: UMIN000047658