Comparison of muscle activity while using different input devices in digital pathology

The high prevalence of musculoskeletal disorders in pathologists, together with the current trend towards the digitization of pathology, prompted us to study the different types of input devices employed during the revision of whole slide images, in order to investigate the pattern and extent of muscle activity involved in their use.

A comparative study was made of 10 input devices (conventional and vertical mouse, three trackballs, the Ergopointer™, the Rollermouse™, an optical pen mouse, a touchpad, and the Leap Motion™). Six medical students performed a standardized circuit using a Fitts' Law based tissue array, digitized. The electrical activity of seven upper limb muscles (adductor pollicis, extensor pollicis longus, extensor digitorum, flexor digitorum, middle deltoid, upper trapezius, and middle trapezius) was measured using surface electromyography.

Statistically significant differences in the overall electrical activity among the different input devices, both absolute values in mV as well as normalized values to the upper limb at rest, were observed (p<0.001); the Rollermouse™ (0.1027mV; 139%), Logitech M570 trackball (0.1053mV; 145%), Ergopointer™ (0.1151mV; 167%), conventional mouse (0.1251mV; 191%), and vertical mouse (0.1312mV; 205%) required less activity, while the optical pen mouse (0.1717mV; 299%), Leap Motion™ (0.1803mV; 319%), Expert Mouse trackball (0.1845mV; 329%), EIGIIS trackball (0.2442mV; 468%) and the touchpad (0.2560mV; 496%) required greater muscle mobilization.

We designed a system based on Fitts' Law to compare input devices in digital pathology. Variability between compared devices and muscle activity was found. Long-term use could result in different muscular fatigue patterns. Even though the selection of an input device is a matter of personal preference, its impact on ergonomics should be considered.