Changes in Biomechanical Factors Depending on Smartphone Usage Configurations

Objective: This study analyzes changes in biomechanical factors, depending on several smartphone usage configurations.<br/>Background: Positioning a smartphone at an appropriate screen height and tilt angle using a holder could reduce physical stress for the user.<br/>Method: Twelve participants watched videos using a smartphone in a recliner chair, with eight configurations (four screen heights, each with the presence or absence of a holder). The head flexion angle, head forward movement, viewing distance, and screen tilt angle were determined from marker data using a motion capture system. Muscular activities were recorded with electromyography sensors. <br/>Results: The preferred screen height of participants using a holder was almost eye level, whereas when the holder was not used, it was approximately 15cm below eye level. The head flexion angle, head forward movement, and vertical viewing distance increased because the screen height was below eye level. The horizontal viewing distance with the holder was approximately 38±6cm, 1.27 times longer than that of 30±6cm when the holder was not used. The activities of the upper limb muscles decreased significantly when the holder was used.<br/>Conclusion: The screen height and tilt angle showed a strong linear relationship. The simple linear regression equation for estimating the screen angle from the screen height was determined. Positioning a smartphone using a holder would reduce muscular pain and relieve visual discomfort for users through a longer viewing distance.<br/>Application: The results of this study could provide design guidelines for developing a holder to adjust the smartphone screen height and screen tilt appropriately.