The effects of valve-handwheel height and angle on neck, shoulder, and back muscle loading

Abstract

The objectives of this research were to: (1) investigate the effects of handwheel height and angle of a valve on the muscle loading of shoulder, neck, and back muscles; and (2) identify a handwheel height and angle that best distributes the load of torque exertions to different muscles. Fifteen healthy male participants were recruited for this study. The handwheel heights included knee, elbow, shoulder, and overhead levels. The handwheel angles included 0°, 45°, and 90°. At each height-angle combination, participants performed an isometric torque exertion on a handwheel. During each trial, the maximum electromyography (EMG) activities were measured from the right and left anterior deltoids, trapezii, latissimi dorsi, and erector spinae muscles. EMG data were normalized and reported as percentages of reference contractions (RC). A two factor split-plot analysis of variance (ANOVA) and Tukey multiple pairwise comparison tests were performed to determine the significant effects. Results show that a handwheel at overhead 45°, which allows the greatest torque production, is associated with a concentrated load on the right anterior deltoid (94.1 %RC). At elbow level, participants were exposed to low loads on the shoulder and neck muscles, but that was compensated with higher loads on the back muscles. Based on the EMG results, the best handwheel height and angle appeared to be at shoulder 0°. At this height and angle, seven of the eight muscles were working at or close to their lowest EMG activities, while also allowing the production of relatively large torques (65.2 Nm).