Masseter muscle hyperactivity and pain sensitization during smartphone use: A cross-sectional study of thenar-trigeminal interaction

Background While it is known that smartphone use (SU) affects the musculoskeletal system, the effect of repetitive thumb movements on the masseter muscle has not been systematically investigated. Objective To investigate the effects of repetitive thumb movements due to SU on the masseter muscle through thenar muscle activity. Methods The students' pressure pain thresholds of the thenar and masseter muscles were assessed with an algometer, and bilateral masseter muscle activation was assessed with Electromyography (EMG). Students were asked to perform repetitive thumb taps with their dominant hand for 5 min using the "Fast-Tap" smartphone application. Results This cross- sectional observational study included 105 students aged 20.96 (2.44) years. Post-SU, right thenar (p < .001), right masseter (p < .001), and left masseter (p = .040) pressure pain threshold decreased, and right masseter muscle activation was higher in terms of %MVC values (p < .001). The right and left thenar and masseter muscle pressure pain thresholds were moderately to highly correlated (p < 0.001). Additionally, the number of thumb taps was moderately correlated with right masseter muscle activation (p < 0.001) and weakly correlated with left masseter muscle activation (p = .005). Conclusion Repetitive thumb movements due to SU may affect the masseter muscle, and the thenar-masseter relationship may lead to innovative treatment approaches in the future.