Multi-touch screens are popular and upper-limb posture is an important safety issue. This study therefore presents an ergonomic investigation of the visual performance of multi-touch screens and the upper-limb postures adopted while using them. The visual performance associated with viewing the text on the screen at 14 angles is experimentally examined. The muscle fatigue in the neck is explored using EMG measurements at different neck bending downwards. In the third experiment, the relationship between muscle fatigue and upper-limb posture while the touch-screen is being used, is examined. Statistical analysis reveals that: （1）the best visual performance is achieved when the screen angle is set between 30 and 120 degrees; （2）according to EMG measurements, the lowest muscle fatigue is when the neck is bent downward at 90°, following by a bending angle of 75°, followed by a bending angle of 60°; muscle fatigue is high when the neck angle is downward at 45°; （3）（a）the Trapeziu and Deltoid exhibit the greatest muscular effort; （b）fingers can be used as a local support on the edge of the screen for pointing-and-clicking; （c）users’ bodies tend to lean forward toward screen during pointing-and-clicking; （d）users use two hand gestures（one with the index and middle fingers, and one with the thumb and middle finger）to zoom in on, rotate and drag objects on the screen, and （e）unnatural postures are adopted when the multi-screen is used, causing users to complain about musculoskeletal disorders.
