Short-term Changes in Upper Extremity Dynamic Mechanical Properties Associated with Power Hand Tool Use

Abstract

This study investigated the relationship between repetitive eccentric exertions in power hand tool operation and upper limb mechanical properties including stiffness and inertial mass, and physiologic measures including localized pain, discomfort, and swelling. Tool parameters, including peak torque (3 Nm and 9 Nm) and torque build up time (50 ms and 250 ms), were controlled in a full-factorial design. Twenty-nine participants were randomly assigned to one of the four conditions and operated a pistol grip nutrunner four times per minute for one hour in the laboratory. An average decrease in stiffness (48%) and mass moment of inertia (60%) of the upper limb was observed immediately following pistol grip nutrunner operation. A previously developed dynamic tool operator model was used to predict resulting handle force and displacement, and the conditions associated with the greatest handle force and displacement demonstrated the greatest decrease in mechanical stiffness and inertial mass, and the greatest increase in localized discomfort.