Affiliations: Ergonomics Division - Institute of Production
Engineering, University of Siegen, Siegen, Germany.
Note:  Corresponding author: Helmut Strasser, Ergonomics Division -
Institute of Production Engineering, University of Siegen, Paul-Bonatz-Str.
9-11, 57068 Siegen, Germany. E-mail: email@example.com.
Abstract: The focus of this research was to investigate how maximum torque and
muscle forces were affected by pronation and supination, i.e., inward and
outward rotation of the forearm in a series of screwdriver tests with 6 varied
handles. Consecutively, maximum torque for pronation and supination was
determined, submaximum isometric levels of torque were demanded, and, finally,
an equal dynamic screwing work for all subjects was simulated. Physiological
cost of performance was simultaneously measured by registrations of
electromyographic activities (EA) from 4 muscles, which were expected to be
involved intensively in screwing tasks. Significant and essential differences
between maximum torque values produced by pronation and supination of the right
and the left arm of the mainly right-handed subjects were found. For clockwise
work, as it is necessary e.g., for driving in screws, inward rotations
(pronations) of the nondominant hand are at least as strong as outward
rotations of the dominant hand. Differences of about 8% favour of pronations
were found. Yet, for counter clockwise work involved e.g., in removing a
tightened screw, inward rotations of the dominant hand yielded a much more
stronger torque strength than outward rotations of the nondominant hand.
Differences of more than 50% right-handed subjects were measured. Also, EA
values of the 4 muscles monitored on the right arm differed significantly.
Systematically operational and physiological differences due to the varied
screwdriver grips, as results of investigations which were not the main
objective of the study, corresponded well with the findings of prior