Gorilla Arm

A well-documented ergonomic phenomenon in which sustained unsupported arm elevation — typical of mid-air touchscreen, vertical display, or extended reality (XR) gesture interaction — produces rapid shoulder fatigue, pain, and performance decline. The term captures the ache and weakness users feel after holding an arm outstretched or above shoulder height for more than a few seconds. Gorilla arm is a key reason that mid-air gesture vocabularies inherited from VR and enterprise AR fail in everyday, long-duration AR-glasses use, and it motivates design moves toward elbow-anchored, chest-level interaction envelopes, proximal stabilization, and alternative input modalities such as wrist-worn EMG or voice.