Background:
Nowadays, smartphones and tablet PCs are increasingly used than desktops. Concurrently, more people are experiencing neck pain with use of those mobile devices. However, it has not be investigated how work with mobile devices alter kinematics of the neck compared with works with keyboard or mouse and how it is associated with mechanical symptoms
Objectives: To quantitatively observe different kinematics of 4 different works with keyboard, mouse, smartphone, and tablet PC by motion capture analysis and to investigate correlation of clinical symptoms with cervical kinematics according to type of works.
Methods: Fifteen healthy adult volunteers were recruited. Subjects were placed in a room equipped with optical marker motion capture system. They were instructed to undergo 4 different tasks with attention in random order for 20 minutes for each: game or typing with smartphone, tablet PC, keyboard, and mouse; mobile devices refer to smartphone and tablet PC while desktop PCs does keyboard and mouse. Motion analysis calculated orientation and location of the trunk and head using rotational matrix. Relative rotation of the head against the trunk were translated into flexion/extension, axial rotation, lateral bending of the neck using Euler angle. Anterior translation of the neck was calculated based on relative location of the head to the trunk. Total movement during a task was a sum of neck movement at each time interval for a task. Mechanical neck symptoms were surveyed before and after each task with regard to items: discomfort, pain tension, and fatigue using VAS scale. Kinematic variables were compared using ANOVA and t-test. Correlation between neck kinematics and mechanical symptoms were analyzed by linear mixed model.
Results: Participants showed larger flexion when using mobile devices compared to desktop PCs by 39.0 degree. Participants also showed greater anterior translation and total movement when using mobile devices compared to using desktop PCs. Axial rotation or lateral bending were not significantly different between tasks. Participants reported more pain, tension and fatigue after works with mobile devices than desktop PCs. Discomforts were not statistically different between tasks. Flexion and anterior translation showed significant correlation with mechanical symptoms after work independent of type of tasks.
Conclusions: Work with smartphones or tablet PCs prompt larger flexion and anterior translation compared with works with keyboard and mouse. Amount of flexion and anterior translation correlates with pain, fatigue, and tension after tasks. Flexion and anterior translation caused by mobile devices may be a direct cause clinical neck symptoms.
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