The effect of hands synchronicity on users perceived arms Fatigue in Virtual reality environment

The use of virtual reality (VR) system has become more common with the arrival of a new generation of headsets. This increase in accessibility has in turn led to VR being used for applications which require longer sessions, such as video games, artistic expression, rehabilitation, and so on. Taking muscular fatigue in account for the VR applications is therefore becoming essential to ensure a comfort of usage and also to avoid injuries. In addition, usual interactions in these diverse applications are very varied and may require the use of one or two hands, synchronized or not. However, little research has focused on fatigue produced by one and two handed interactions especially during mid-air interaction in VR environment. In this paper, we examine the effect of hands synchronicity and movement direction on the user perceived arm fatigue in VR environment during a simple (one line of targets) and a composite (two lines of targets) pointing tasks performed using both controlled and free hands synchronicity. Our findings indicate that to optimize the relationship between fatigue and efficiency, it seems necessary to select the synchronicity of hands depending on the performed task. Furthermore, it is desirable to permit the users to use the hands synchronicity they prefer. In addition, distance covered by the hand and changes in user posture could be used in real-time as indicators of fatigue to trigger changes in the interface, or notifications. Finally, our findings reveal that the directions of movement along the vertical axis and some diagonals are more tiring than those of the horizontal plane, which suggests that it would be better to favor the use of horizontal directions.