Examining kinematics and muscle activity of the upper extremity while performing cleaning tasks: A pre-post shift evaluation

Custodians engage in strenuous manual labour throughout their workday. Uncertainty exists on whether kinematics or muscle activation changes as workers progress through their shift. The purpose of this study was to examine muscle activation and upper extremity kinematics during typical custodial tasks performed at the start and end of the work shift. Electromyography (EMG) of 8 torso and upper extremity muscles and motion capture of the corresponding region were collected for 10 custodial participants while they completed garbage removal, dry mopping, and vacuuming tasks at the start and end of a work shift. The start of shift assessment demonstrated larger anterior deltoid, posterior deltoid and extensor digitorum activation by up to 12.6 %maximal voluntary contraction (%MVC) (p < 0.001–0.023). Task affected mean and peak EMG in all muscles except flexor digitorum (p < 0.001–0.0293), and the greatest activation was found during vacuuming (peak <55%MVC in anterior and middle deltoid) and the heaviest garbage removal task (84% MVC peak in upper trapezius). Mopping created the lowest amounts of activation for almost all muscles. Joint range of motion (p < 0.001–0.031) in the shoulder was highest in vacuuming, while trunk flexion was largest in garbage removal tasks. This work replicated common custodial tasks in a laboratory, using actual custodial workers at times relevant to their typical work shifts. The information presented is useful for ergonomists, work tasks designers and custodial administration staff to develop guidelines for injury prevention.     

Shoulder and neck complaints in customer relations: individual risk factors and perceived exposures at work

Perceived psychosocial and biomechanical exposures, individual factors and pain in the shoulder and neck were recorded in two groups of female service workers (healthcare and shopping centre workers). The jobs investigated were characterized by ‘much’ direct human relations, ‘little’ sitting and ‘much’ standing, and were light work by physiological or biomechanical criteria but potentially psychosocially demanding. A screening survey (n = 400 females) was the basis for the selected sample (n = 66 females), which was the object of the main investigation of this study. Reliability of the questionnaires was tested in a separate group of female healthcare workers (n = 29). Heart rate recordings through the work day estimated workload. There was a high prevalence of shoulder and neck pain (>50%) for both work groups. In the two populations it proved difficult to explain shoulder and neck pain by reported physical and psychosocial exposures or individual factors, except by the variable ‘perceived general tension’, which clearly differentiated workers with and without pain. The findings in this study indicated, first, that perceived general tension might be an independent risk factor for muscle pain and, second, that this might be related to personality factors. However, this putative relationship must be verified in a longitudinal study. As no variable describing exposures in the working environment was associated with shoulder and neck pain, the question is posed whether such complaints can be considered work-related. Alternatively, the variables used to describe mechanical and psychosocial exposures in this study may have low specificity in characterizing work-related risk factors for service workers with customer relations.     

Biomechanical assessment of lateral stiffness elements in the suspension system of a backpack

The purpose of this study was to examine the change in load distribution characteristics associated with adding lateral stiffness elements (rods) to a rucksack (backpack). A load distribution mannequin was instrumented with two 3D load cells to allow determination of the load applied to the shoulders and upper torso independent of the load applied to the hips and lower trunk. Position and mass of the payload (25?kg) were fixed at the centre of the volume of the rucksack and held constant during all testing. It was hypothesized that lateral rods would provide a force bridge that transfers part of the vertical load of the pack from the upper back and shoulders to the hip belt thereby reducing the vertical load on the torso, and possibly reducing the horizontal reaction force that produces a shear load on the spine. Results showed that these active stiffness elements shifted 14% of the vertical load from the upper torso to the pelvic region with lumbar shear load remaining relatively unchanged for all combinations of shoulder strap and waist belt tension. The lateral rods also provided a mean increase of 12% in the extensor moment at the L3?–?L4 level, thus reducing some demand on the erector spinae muscles.     

Effects of arm support on shoulder and arm muscle activity during sedentary work

The aim of this study was to evaluate different arm supports by comparing the activity of shoulder and arm muscles during various work tasks, with and without the lower arm supported. Twelve female subjects, aged between 23 and 37 years, were asked to perform three types of tasks: typing, simulated assembly work (in two different positions), and pipetting. The supports used were: fixed arm support (FIX), horizontal movable arm support (HOR), and spring-loaded arm support (SLA). During the experiments, the electromyograms (EMG) of four muscles were simultaneously recorded: m. deltoideus anterior and lateralis, m. trapezius pars descendens and m. extensor carpi radialis brevis. Normalization was made against maximum isometric contraction. The mean values of the normalized EMG levels showed a reduced EMG level of the shoulder muscles when using arm supports in all the tasks, and for all muscles but the wrist extensor, compared to the EMG levels without arm supports. The horizontal movable support was more effective in reducing the EMG levels of the shoulder muscles than other arm supports, in tasks at table height. Thus, it is possible to reduce muscle activity of the shoulder region by using arm supports. Further research is needed to make biomechanical calculations to compare the EMG level of these muscles using suspension and the effects of inclination of work task.     

Impact of pulling direction and magnitude of force exertion on the activation of shoulder muscles

Shoulder musculoskeletal disorders (MSD) are frequently associated with the work activities that demand forceful arm exertions in pushing and pulling directions. Considering the ability of shoulder joint to exert forces in nearly any direction, our understanding of the shoulder muscles activation as affected by pushing and pulling exertions is limited. In this study the activation of seven shoulder muscles were studied for 10 male participants during pulling exertions performed in five directions (pull right, pull left, pull back, pull down and pull up) using three force levels (22.24 N, 33.36 N and 44.48 N). Exertions performed in pulling right and pulling up directions produced higher activation and received higher perceived exertion ratings than the exertions performed in the other directions. Rotator cuff and middle deltoid muscles activation were consistently higher during pulling up and pulling right exertions compared to the other muscles. A high correlation was found between the activation of rotator cuff and deltoid muscles and the perceived exertion ratings. The rotator cuff and middle deltoid muscles activation observed during the pulling up and pulling right exertions can be explained by the concavity compression mechanism which stabilizes the glenohumeral joint of shoulder.Relevance to industryThe muscle activation data expressed in terms of Maximum Voluntary Contraction (MVC) and perceived exertion ratings are widely used by the ergonomic practitioners to design and/or evaluate workplace exertions. This study provides such data for several shoulder muscles during pulling exertions performed under different conditions.     

Output-associative RVM regression for dimensional and continuous emotion prediction

Many problems in machine learning and computer vision consist of predicting multi-dimensional output vectors given a specific set of input features. In many of these problems, there exist inherent temporal and spatial dependencies between the output vectors, as well as repeating output patterns and input–output associations, that can provide more robust and accurate predictors when modeled properly. With this intrinsic motivation, we propose a novel Output-Associative Relevance Vector Machine (OA-RVM) regression framework that augments the traditional RVM regression by being able to learn non-linear input and output dependencies. Instead of depending solely on the input patterns, OA-RVM models output covariances within a predefined temporal window, thus capturing past, current and future context. As a result, output patterns manifested in the training data are captured within a formal probabilistic framework, and subsequently used during inference. As a proof of concept, we target the highly challenging problem of dimensional and continuous prediction of emotions, and evaluate the proposed framework by focusing on the case of multiple nonverbal cues, namely facial expressions, shoulder movements and audio cues. We demonstrate the advantages of the proposed OA-RVM regression by performing subject-independent evaluation using the SAL database that constitutes naturalistic conversational interactions. The experimental results show that OA-RVM regression outperforms the traditional RVM and SVM regression approaches in terms of accuracy of the prediction (evaluated using the Root Mean Squared Error) and structure of the prediction (evaluated using the correlation coefficient), generating more accurate and robust prediction models.     

Further studies of shoulder and neck pain and exposures in customer service work with low biomechanical demands

The aim of the study was to establish insight into work exposures that cause shoulder and neck pain among occupational groups that have low biomechanical exposure and experience work stress from client/customer contact, among other exposures. Four occupational groups were studied, in health care (n = 20), retail (n = 22), banking (n = 26), and university secretaries (n = 26), a total of 94 volunteers. Thirty-nine were classified as pain-afflicted in the shoulder and neck, while 55 were pain-free. The subjects' perceptions of biomechanical and psychosocial exposures were established by use of quantitative questionnaires and by explorative interviews with open-ended questions, covering the same themes. Heart rate and trapezius EMG were recorded over a full workday and the following leisure period. Trapezius median and static activity during work were 3.3% and 0.3% EMG_max, only marginally higher than trapezius activity in the leisure period (2.7% and 0.2% EMG_max). The quantitative questionnaire did not identify any variable that correlated with shoulder and neck pain except perceived general tension. The interviews established that the interaction with clients or customers was an important source of work stress. Such stress appeared to be a complex entity not easily characterized by established psychosocial questionnaires. The physiological variables were at most weakly elevated in periods with high stress as compared to periods with low stress. The authors caution against relying on standardized quantitative questionnaires and/or physiological recordings to characterize work stress in occupations with emotional stress through client/customer service work.     

小型弹箭惯性矩的测定

叙述了三线摆的结构原理 ,介绍了该摆小角与大角摆动周期的计算方法。利用三线摆的结构原理可以测量小型弹箭、子弹头、飞机模型及其他构件的惯性矩。当 R/ L <1 / 30 ,φ0 ≤ 60°时 ,该装置的测量精确度可优于 1 %。     

Dual-Rotation Speed Friction Stir Welding: Experimentation and Modeling

Implementing differential rotation speeds of pin and shoulder in the friction stir welding process is considered. Experimental investigations were carried out using a newly designed and fabricated apparatus for dual-rotation speed friction stir welding. Metallographic studies demonstrated that appropriate selection of separate pin and the shoulder rotation speeds not only results in defect-free joints, but also affects the weld zone by controlling the heat input delivered. An energy model for predicting maximum temperature was extended to the dual-rotation speed friction stir process. The model was verified using the previous experimental results reported in the literature.     

Long-duration assessment of upper arm posture and motion and their association with perceived symptoms among bakery workers

Awkward shoulder postures have been suggested to be a cause of shoulder discomfort among bakery workers. This study aimed at long-duration assessment of upper arms posture and motion and their association with perceived symptoms among bakery workers. Among workers in three types of bread systems, fifty-seven bakers were randomly selected. The self-reported rates for the perceived severity and frequency of shoulder discomfort were collected through questionnaires. Working postures and movements of the shoulders during work were continuously recorded with inclinometry measurements for three hours. Percentage of time spent with the upper arm right elevated more than 60° was significantly correlated with the perceived discomfort rate in the right shoulder for all bakery workers (r = 0.48 to 0.63, p ≤ 0.05). A significant correlation was found between angular velocity with the perceived discomfort intensity for right upper arm.(r = 0.60 to 0.87, ≤0.005) of all workers in the three baking systems. Physical exposure in bakers was characterized by significantly more awkward postures and the percentage of time spent with the upper arms elevated more than 60°. The current findings can facilitate more informed decisions with respect to both engineering (e.g.ergonomic workstation and tool design) and administration (e.g. work organization) control strategies.