The purpose of this work was to validate an addition to a dynamic armrest design (DA) for use during inward–outward and fore–aft joystick manipulation. The design was validated compared to a stationary armrest (SA) and no armrest (NA) using surface electromyography (EMG) and a questionnaire. The DA was not successful in reducing muscle activation for inward–outward movements when compared to the SA. Furthermore, the addition of inward–outward dynamic portion negated the improvements seen with the fore–aft dynamic armrest design. Despite the lack of significant muscular activation findings, most participants preferred the DA to the SA or NA. However, unlike the fore–aft dynamic armrest, which was found to successfully reduce muscle activation in multiple muscles involved in joystick manipulation, results suggest that the horizontally dynamic support addition may not be necessary for inward and outward joystick movements.

BACKGROUND: Joystick operators often experience constant low level muscle loading in the upper limb when using joysticks, which can lead to repetitive strain injuries. It has been hypothesized that the strain on the muscles may be reduced by supporting the arm during joystick manipulation. OBJECTIVE: To design a horizontally dynamic armrest which appropriately supports the motion of the forearm during sideto-side joystick movements. METHODS: The paper describes the process used to design a dynamic armrest which appropriately supports an operator's arm throughout the range of side-to-side joystick movements. RESULTS: The trajectory of the elbow and wrist during these joystick movements was determined, and a new horizontally dynamic armrest designed and built. CONCLUSIONS: Most heavy mobile equipment seat armrests fail to provide appropriate support throughout the range of joystick motion resulting in constant upper body muscle loading. Our paper describes the development of a dynamic armrest which is designed to provide appropriate support throughout side-to-side joystick movements.