Electromyographic Evaluation of Muscle Strain of the Hand-Arm-Shoulder System during Alternating Typing at a Conventional and an Ergonomic Keyboard

Abstract

Manufacturers of ergonomic split keyboards promise maximum effectiveness and comfort as well as a reduction of physical complaints. In order to determine the claimed positive effects, 10 male subjects (Ss) participated in standardized working tests during which they entered text into a PC, alternatingly using a conventional keyboard and the test keyboard. Electromyographic activity (EA) of 8 muscle groups was simultaneously recorded during altogether 6 working phases with a duration of 10 min, each. Measurements of the maximum activity EA_max via maximum voluntary contractions of the 8 muscles — which were necessary for calculating standardized electromyographic activity (sEA) used to represent muscle strain as a percentage — were always taken at the end of the experiment. Muscle strain varied from muscle to muscle but the level of the sEA-values for the different muscles was reproducible and stable. Also, activation of most muscles acting on the shoulder, upper arm, forearm, and the hand showed differences which, though small in amount, could be statistically secured and associated with the keyboard type. The ergonomic design of the tested keyboard led to objectively verifiable and plausible reductions of muscle strain.