UXTony Stark doesn't feel it because he's a fictional billionaire. You will.
The fatigue caused by interfaces that require sustained physical effort to operate. Named for the ape-like posture required by sustained touchscreen use, it's the reason gesture-based interfaces look better in movies than in offices. The best interface keeps your arms where they want to be: at your sides.
Physical fatigue caused by interfaces requiring sustained arm elevation, first identified in the 1980s and still present in modern touchscreen and gesture-based systems.