The effect of an active steering system on city bus drivers’ muscle activity

City bus drivers spend hours driving under time pressure, in congested traffic and in a monotonous sitting position. This leads to unhealthy working conditions, especially in terms of physical and psychological stress. The aim of this study is to investigate whether an active steering system can alleviate the musculoskeletal stress involved in manoeuvring a bus. Twenty bus drivers drove a city bus equipped with the Volvo dynamic steering (VDS) support system in real traffic. Steering effort was evaluated with electromyography and with a questionnaire. Compared to baseline, VDS significantly reduced the required muscle activity by on average 15–25% while turning, and up to 68% in the part of the manoeuvre requiring maximum effort. The bus drivers believed that VDS will help reduce neck and shoulder problems, and they expressed a desire to have VDS installed in their own bus.     

Repeatability of electromyography normalization of the neck and shoulder muscles in symptomatic office workers

Purpose. The purpose of the study was to examine the repeatability of electromyography (EMG) normalization in office workers with neck and shoulder symptoms. Methods. Fifteen female office workers with neck/shoulder symptoms were recruited to participate in two separate days of testing. Maximum voluntary isometric contraction (MVIC) was used for the normalization of EMG data on the following muscles: cervical erector spinae, upper trapezius, lower trapezius and anterior deltoid. Repeatability was calculated using the intra-class correlation (ICC), relative standard error of measurement (%SEM) and relative coefficient of variation (%CV). Results. Peak root mean square (rms) and median frequency (MF) showed good to high repeatability in the UT, AD and CES (ICC?=?0.87–0.95, %SEM=?2.65–9.48, %CV=?0.2–5.9). The repeatability of peak rms was good (ICC?=?0.87, %SEM?=?12.56, %CV?=?3.3) and the MF of the LT was fair (ICC?=?0.76, %SEM?=?5.71, %CV?=?2.9). Conclusion. Peak rms and MF from the MVIC normalization method can be measured with sufficient repeatability in symptomatic office workers.     

Infrared thermography reveals effect of working posture on skin temperature in office workers

Introduction. Musculoskeletal symptoms related to using traditional computer workstations are common. Quantitative methods for measuring muscle stress and strain are needed to improve ergonomics of workstations. We hypothesize that infrared thermography (IRT) is suited for this purpose. Methods. This hypothesis was evaluated by estimating muscle activity in upright and traditional working postures with IRT and surface electromyography (sEMG). IRT and sEMG measurements were conducted in 14 female participants with both working postures. First, measurements with the traditional posture were performed. Later, participants had 1?month to adjust to the upright working posture before repeating the measurements. IRT images were acquired before and after a full working day, with sEMG recordings being conducted throughout the measurement days. Participants evaluated their neck pain severity using neck disability index (NDI) questionnaires before the first and after the second measurement day. Results. Spatial variation in upper back temperature was higher (p?=?0.008) when working in traditional posture and the upright working posture reduced (p?p?=?0.003) after working in the upright posture. Conclusion. IRT was found suitable for evaluating muscle activity and upright working posture to reduce the NDI and muscle activity in the upper back.     

Upper trapezius fatigue in carpet weaving: the impact of a repetitive task cycle

Introduction. Shoulder disorders are one of the most prevalent musculoskeletal disorders among carpet weavers. The most important cause of these disorders is muscle fatigue. The aim of the present study is to investigate the effect of carpet weaving characteristics on upper trapezius (UTr) muscle fatigue during a task cycle. Method. In this cross-sectional study, 9 women and 3 men participated. During an 80-min cycle of carpet weaving, a times-series model was applied to assess electromyography amplitude and frequency changes. Result. According to the joint analysis of electromyogram spectrum and amplitude method, the participants experienced 0% force decrease, 0.9% recovery, 18% force increase and 72% fatigue in the left UTr. Furthermore, the rates of force decrease, recovery, force increase and fatigue in the right UTr were 18%, 18%, 18% and 45%, respectively. Fatigue in the right and the left UTr was reported to be the dominant state during one carpet weaving task cycle. Conclusion. Task cycle appears to have a significant impact on UTr fatigue in participants, and UTr fatigue can be considered a serious risk factor in shoulder musculoskeletal disorders. Hence, further studies should focus on better workstations and work–rest periods during various subtasks.     

Development of statistical models for predicting muscle and mental activities during repetitive precision tasks

This study was conducted to develop muscle and mental activities on repetitive precision tasks. A laboratory experiment was used to address the objectives. Surface electromyography was used to measure muscle activities from eight upper limb muscles, while electroencephalography recorded mental activities from six channels. Fourteen university students participated in the study. The results show that muscle and mental activities increase for all tasks, indicating the occurrence of muscle and mental fatigue. A linear relationship between muscle activity, mental activity and time was found while subjects were performing the task. Thus, models were developed using those variables. The models were found valid after validation using other students’ and workers’ data. Findings from this study can contribute as a reference for future studies investigating muscle and mental activity and can be applied in industry as guidelines to manage muscle and mental fatigue, especially to manage job schedules and rotation.     

Effects of Ergorest® Arm Supports on Muscle Strain and Wrist Positions During the Use of the Mouse and Keyboard in Work With Visual Display Units: A Work Site Intervention

The effects of Ergorest^® arm supports on wrist angles and musculoskeletal strain in the neck-shoulder-arm region and electrical activity in the shoulder and arm muscles were studied during typing or the use of the mouse in work with a visual display unit (VDU). Twenty-one women were randomized into 3 groups (1 arm support, 2 arm supports, and control). Measurements were carried out before and after the 6-week intervention. The wrist extension of the mouse hand, the muscle activity of the trapezius muscle, and the subjective discomfort ratings indicated that 2 arm supports were better than 1 in work with a mouse. The Ergorest^® arm support alleviates muscle and joint strain in VDU work when used for both arms.     

井下支护作业人员颈部肌肉疲劳特性研究*

为探究井下支护作业人员颈部肌肉疲劳受伸张和屈曲角度变化的影响,采用表面肌电法（sEMG）实验模拟测量7种点位角度下,颈部夹肌、斜方肌以及胸锁乳突肌在不同作业频率时的疲劳情况,以积分肌电值(iEMG)及中值频率（MF）评价各肌肉疲劳程度。研究结果表明:低频实验中随点位角度的增大,颈部屈曲活动时,胸锁乳突肌疲劳变化明显,iEMG疲劳前后差值最大为1.55,MF下降率最大为0.60;颈部伸展活动时,夹肌疲劳变化明显,iEMG疲劳前后差值最大为1.59,MF下降率最大为0.59;斜方肌未表现出明显疲劳变化规律。高频实验相较低频实验疲劳发生速度加快,疲劳积累程度显著提升,颈部活动主要肌肉疲劳发生时间由16~19 min提前至13~17 min,各肌肉MF下降速度为低频实验的1~1.55倍。     

Variability of Musculoskeletal Strain on Dentists: An Electromyographic and Goniometric Study

Introduction. Dentists and hygienists are strongly affected by musculoskeletal disorders (MSDs). As workstation concepts are supported by subjective arguments only, the aim of this study was to use objective measurements to compare the variability of strain in various concepts: a dental chair equipped with a cart or an over-the-patient delivery system without an assistant, and Dr Daryl Beach’s concept with an assistant. Methods. Goniometric and electromyographic recordings were made on 8 subjects, during a scaling operation. The electrical activity of their trapezius and lumbar muscles was compared, as were their cervical and lumbar ranges of motion. Results. The results showed that there was a wide variability depending on the workstation. However, the Beach concept tended to reduce physical strain on most parameters: duration of left lumbar muscle activity (2% compared to 15% of time spent in >10% maximal voluntary contraction, MVC), time spent in cervical side bending (4% compared to 30%), cervical flexion of >20° (9% compared to 40%), and left trapezius activity (9% of time spent >10% MVC compared to 28%). Conclusion. Practitioners and students should adjust their workstations to reduce the prevalence of MSDs.     

Combining Psychophysical Measures of Discomfort and Electromyography for the Evaluation of a New Automotive Seating Concept

The purpose of this study was to determine if the advantages and disadvantages of a new automotive seating concept, known as the micro-adjuster control system, could be reliably evaluated using both a physiological assessment technique (i.e., electromyography [EMG]) and a subjective questionnaire. The results indicate that psychophysical measures of discomfort and the root mean squared (RMS) activity of the EMG are statistically related, r (8) = ?.788, p = .020. More specifically, subjective perceptions of comfort were found to improve with decreasing levels of muscle activity. This implies that seat comfort can be evaluated on the basis of physiological as well as subjective responses to prolonged driving. This finding should drastically improve automobile seat design efforts.