Jack Dennerlein

Gender Differences in Exposure to Physical Risk Factors during Standardized Computer Tasks

The aim of this study was to determine whether there were differences in exposure to physical risk factors between genders in a series of standardized laboratory-based tasks on computer workstations adjusted to wubject anthropometry. METHODS: Thirty computer users (15 men and 15 women) completed five different tasks. Surface electromyography measured muscular activity in the shoulders (anterior deltoid, medial deltoid, and trapezius) and wrists (extensor carpi radialis, extensor carpi ulnaris, flexor carpi radialis, and flexor carpi ulnaris). Electrogoniometers and electromagnetic sensors measured posture of the wrists and shoulders, respectively. A force-sensing platform placed under the keyboard measured typing force. Whole body and upper extremity anthropometric measurements were recorded manually. RESULTS: Normalized muscle activity (EMG), the forces applied to the keyboard relative to the maximum force of the fingertip (%MVC), and range of motion were consistently higher for women. Shoulder posture was less neutral for women. Pearson correlations revealed strong associations between anthropometric variables (height, shoulder width, and arm length) and physical risk factors (EMG, range of motion, force) that are different between genders. CONCLUSIONS: Women have greater exposure to physical risk factors during identical tasks on a computer workstation. Exposure to these risk factors was strongly correlated to anthropometric differences between genders. This demonstrates how biomechanics plays a role and may contribute to the higher prevalence of upper extremity musculoskeletal disorders found in females.

P128 Whole-body vibration among mining heavy-vehicle operators is associated with back pain-related absenteeism

Background Whole body vibration (WBV) has been related to back pain in professional vehicle operators; however, more evidence is needed to better establish the direct link between WBV exposure and back pain-related absenteeism. Aim We tested the association between WBV exposure and absenteeism in a population of mining heavy equipment vehicle (HEV) operators who used an array of different HEVs using several vibration exposure estimates. Methods The database analysed here included 3 years of absenteeism and vehicle operation logs for 2286 HEV operators. Workers’ exposures per month were estimated from each worker’s vehicle operation log and computing a time-weighted average of A(8), VDV(8) and Sed(8) vibration metrics from WBV directly measured on 11 different types of HEVs in the fleet. These three metrics captured average, shock and static compressive dose of the spine, respectively. Box-Cox regression models tested associations between the different vibration exposure estimates to time-to-absenteeism related to ICD-10 codes 50, 51 and 54, while adjusting for age, seniority, Body Mass Index and exposure duration. Results WBV was positively and significantly associated to absenteeism; however, those associations exist only when exposure duration is included in the models, which is itself not statistically significant in the models. Hazard ratios varied greatly depending on the used exposure metrics (1.02 to 300,000). Generally, exposures based on the A(8) metric, for the Z axis showed larger associations than the other parameters and exposure axes. Also, statistical models using time-varying exposures resulted in larger associations than models using cumulative metrics of exposure estimated to the time of absenteeism or to censoring. Discussion WBV may be a determinant of back pain-related absenteeism and this undesirable effect is likely to occur after a few years of exposure. The evidence suggests that controls aiming at reducing WBV exposure would help directly reducing absenteeism in industry.

EMG Changes of the ECU Muscle with Exposure to Repetitive Ulnar Deviation

Our objective was to quantify changes in muscle EMG activity due to repetitive work. Using a repeated measures design, 13 females participated in 3 conditions, each lasting two eight-hour days: a control inactive condition, and two repetitive work conditions with ulnar deviation tasks at 20 and 25 repetitions per minute. EMG of the extensor carpi ulnaris muscle (ECU) was recorded during voluntary isometric contractions (20% and 60% MVC) eight times throughout the work and control days. The amplitude of the EMG signal was lower on workdays compared to the control days. Initial median frequency of the EMG signal showed no change between the control and workdays; however, the decline of the median frequency with respect to time over the course of each isometric contraction was steeper during workdays compared to control days. These changes suggest that the muscles are in an early stage of fatigue when working for an eight-hour workday.