The effects of shoulder load and pinch force on electromyographic activity and blood flow in the forearm during a pinch task

The object of the current study was to determine whether static contraction of proximal musculature has an effect on the blood flow more distally in the upper extremity. Static contractions of muscles in the neck shoulder region at three levels (relaxed, shoulders elevated and shoulders elevated loaded with 4.95 kg each) were combined with intermittent pinch forces at 0, 10 and 25% of the maximum voluntary contraction (MVC). Blood flow to the forearm was measured with Doppler ultrasound. Myoelectric activity of the forearm and neck-shoulder muscles was recorded to check for the workload levels. Across all levels of shoulder load, blood flow increased significantly with increasing pinch force (21% at 10% MVC and by 44% at 25% MVC). Blood flow was significantly affected by shoulder load, with the lowest blood flow at the highest shoulder load. Interactions of pinch force and shoulder load were not significant. The myoelectric activity of forearm muscles increased with increasing pinch force. The activation of the trapezius muscle decreased with increasing pinch force and increased with increasing shoulder load. The precise mechanisms accounting for the influence of shoulder load remains unclear. The results of this study indicate that shoulder load might influence blood flow to the forearm.     

Job stress management and ergonomic intervention for work-related upper extremity symptoms

In practice the secondary prevention of work-related upper extremity (WRUE) symptoms generally targets biomechanical risk factors. Psychosocial risk factors have also been shown to play an important role in the development of WRUE symptom severity and future disability. The addition of a stress management component to biomechanically focused interventions may result in greater improvements in WRUE symptoms and functional limitations than intervening in the biomechanical risk factors alone. Seventy office workers with WRUE symptoms were randomly assigned to an ergonomics intervention group (assessment and modification of work station and stretching exercises) or a combined ergonomic and job stress intervention group (ergonomic intervention plus two 1-h workshops on the identification and management of workplace stress). Baseline, 3- and 12-month follow-up measures of observed ergonomic risks and self-reported ergonomic risks, job stress, pain, symptoms, functional limitation, and general physical and mental health were obtained from all participants. While both groups experienced significant decreases in pain, symptoms, and functional limitation from baseline to three months with improvements continuing to 12 months post baseline, no significant differences between groups were observed for any outcome measures. Findings indicate that the additional two-session job stress management component did not significantly enhance the short- or long-term improvements brought about by the ergonomic intervention alone.     

Changes in upper extremity biomechanics across different mouse positions in a computer workstation

In order to determine differences in biomechanical risk factors across different mouse positions within computer workstations a repeated measures laboratory study was completed with 30 adults (15 females 15 males). The subjects performed mouse-intensive tasks during two experiments. One experiment examined three mouse positions: a standard mouse (SM) position with the mouse directly to the right of the keyboard; a central mouse (CM) position with the mouse between the keyboard and the body, positioned in the body's mid-sagittal plane; a high mouse (HM) position, which simulated using a keyboard drawer with the mouse on the primary work surface. The second experiment compared two mouse positions: the SM position and a more central position using a keyboard without a number keypad (NM). Electrogoniometers and inclinometers measured wrist and upper arm postures and surface electromyography measured muscle activity of four forearm muscles and three shoulder muscles. The CM mouse position was found to produce the most neutral upper extremity posture across all measures. The HM position produced the least neutral posture and resulted in the highest level of muscle activity. Compared to the SM position, the NM position reduced wrist extension slightly and promoted a more neutral shoulder posture. Little difference in muscle activity was observed between the SM and NM positions. In conclusion, of these alternative mouse positions, the HM position was the least desirable, whereas the CM position reduced overall awkward postures associated with mouse-intensive computer tasks.     

A new method for estimating hand internal loads from external force measurements

This study examines using force vectors measured using a directional strain gauge grip dynamometer for estimating finger flexor tendon tension. Fifty-three right-handed participants (25 males and 28 females) grasped varying-sized instrumented cylinders (2.54, 3.81, 5.08, 6.35 and 7.62 cm diameter) using a maximal voluntary power grip. The grip force vector magnitude and direction, referenced to the third metacarpal, was resolved by taking two orthogonal grip force measurements. A simple biomechanical model incorporating the flexor tendons was used to estimate long finger tendon tension during power grip. The flexor digitorum superficialis and the flexor digitorum profundus were assumed to create a moment about the metacarpal phalange (MCP) joint that equals and counteracts a moment around the MCP joint measured externally by the dynamometer. The model revealed that tendon tension increased by 130% from the smallest size handle to the largest, even though grip force magnitude decreased 36% for the same handles. The study demonstrates that grip force vectors may be useful for estimating internal hand forces.     

Different computer tasks affect the exposure of the upper extremity to biomechanical risk factors

In order to determine differences in biomechanical risk factors across computer tasks, a repeated measures laboratory experiment was completed with 30 touch-typing adults (15 females and 15 males). The participants completed five different computer tasks: typing text, completing an html-based form with text fields, editing text within a document, sorting and resizing objects in a graphics task and browsing and navigating a series of intranet web pages. Electrogoniometers and inclinometers measured wrist and upper arm postures, surface electromyography measured muscle activity of four forearm muscles and three shoulder muscles and a force platform under the keyboard and force-sensing computer mouse measured applied forces. Keyboard-intensive tasks were associated with less neutral wrist postures, larger wrist velocities and accelerations and larger dynamic forearm muscle activity. Mouse-intensive tasks (graphics and intranet web page browsing) were associated with less neutral shoulder postures and less variability in forearm muscle activity. Tasks containing a mixture of mouse and keyboard use (form completion and text editing) were associated with higher shoulder muscle activity, larger range of motion and larger velocities and accelerations of the upper arm. Comparing different types of computer work demonstrates that mouse use is prevalent in most computer tasks and is associated with more constrained and non-neutral postures of the wrist and shoulder compared to keyboarding.     

Gender differences in prevalence of upper extremity musculoskeletal disorders

A literature review was conducted on the current literature base to determine the strength of support for the hypothesis that women experience higher prevalences of upper extremity musculoskeletal disorders (UEMSDs) than men. Fifty-six articles were reviewed for data on gender differences in frequency, incidence or prevalence rates for musculoskeletal disorders specific to the upper extremities. These articles included both general and working populations. The majority of the studies showed that women had significantly higher incidences of various types of UEMSDs than men. This trend was consistently observed in studies based on self-report or plant/workers compensation records, with and without physical examination, and after adjusting for potential confounders such as age and physical work factors. With men as the referent, the odds ratio (OR) or prevalence ratio (PR) for UEMSDs ranged from 0.85 to 10.05 for self report. For self report combined with physical examination, the OR/PR ranged from 0.66 to 11.4. The OR/PR for carpal tunnel syndrome (CTS) ranged from 0.6 to 2.87 with confounder adjustment. These findings suggest that women do have significantly higher prevalences than men for many types of UEMSDs, even after controlling for the type of data source and confounders such as age or work factors.     

Effect of horizontal position of the computer keyboard on upper extremity posture and muscular load during computer work

The distance of the keyboard from the edge of a work surface has been associated with hand and arm pain; however, the variation in postural and muscular effects with the horizontal position have not been explicitly explored in previous studies. It was hypothesized that the wrist approaches more of a neutral posture as the keyboard distance from the edge of table increases. In a laboratory setting, 20 adults completed computer tasks using four workstation configurations: with the keyboard at the edge of the work surface (NEAR), 8 cm from the edge and 15 cm from the edge, the latter condition also with a pad that raised the work surface proximal to the keyboard (FWP). Electrogoniometers and an electromagnetic motion analysis system measured wrist and upper arm postures and surface electromyography measured muscle activity of two forearm and two shoulder muscles. Wrist ulnar deviation decreased by 50% (4°) as the keyboard position moved away from the user. Without a pad, wrist extension increased by 20% (4°) as the keyboard moved away but when the pad was added, wrist extension did not differ from that in the NEAR configuration. Median values of wrist extensor muscle activity decreased by 4% maximum voluntary contraction for the farthest position with a pad (FWP). The upper arm followed suit: flexion increased while abduction and internal rotation decreased as the keyboard was positioned further away from the edge of the table. In order to achieve neutral postures of the upper extremity, the keyboard position in the horizontal plane has an important role and needs to be considered within the context of workstation designs and interventions.     

Biomechanics and Kinematic Responses of the Upper Extremity during Isotonic and Isokinetic Wrench‐Turning Tasks

The purpose of this study was to investigate the impact of using a wrench under isotonic (constant torque) and isokinetic (constant speed) task modes (TM) at three work surface inclinations (WSI) (0°, 45°, and 90°) on the biomechanical (muscle activity) and kinematic (joint posture) responses of the upper extremity. The muscle activity of seven muscles (trapezius posterior deltoid, anterior deltoid, triceps, biceps, brachioradialis, and flexor digitorium) and posture of four body segments (shoulder adduction/abduction, elbow flexion/extension, forearm supination/pronation and wrist flexion/extension) were obtained using surface electromyography and motion tracking, respectively. WSI showed a statistically significant effect on the muscle activity of the posterior deltoid (p = .038), triceps (p = .016), and biceps (p = .021). The least muscle activity was recorded at the 0° WSI in the isotonic TM. WSI had a significant impact on the supination (p = .017) and pronation (p = .011) of the forearm. The 45° WSI had the least impact on forearm postures. Wrenches are widely used in industries, including automobile service and maintenance, manufacturing, carpentry, and general repair work. Their usage poses risks for the development of musculoskeletal disorders in the upper extremity. In spite of this, knowledge of their physical demands and associated impact on the upper extremity has not been well documented. This study provides empirical evidence on the biomechanical and kinematic responses of selected upper extremity muscles and limb segments and highlights task performance and workstation design factors that elicit undue levels of these responses. The results of this work can provide guidance for ergonomic interventions such as optimized task design and/or improved workstation design when it comes to wrench‐turning tasks.     

Effects of backpack and double pack loads on postural stability

Measurement of postural stability is crucial for identifying predictors of performance, determining the efficacy of physical training and rehabilitation techniques and evaluating and preventing injuries, particularly for heavy load carriage in hikers, mountain search and rescue personnel and soldiers. This study investigated the effect of load distribution on postural stability in an upright stance using backpack and double pack loads under conflicting or impaired somatosensory, visual and vestibular conditions. The sensory organisation tests were conducted on 20 young adults before and after a 10-min level walking exercise. Young adults’ ability to use inputs from somatosensory and visual systems to maintain postural stability was significantly reduced following a 10-min walking exercise with a heavy backpack (30% of body weight), whereas no significant changes were observed for double pack carriage. Thus, the distribution of heavy loads to the front and back provides superior balance control compared with back-only loading.

Practitioner summary: This study investigated the effects of heavy (30% of body weight) load distribution on postural stability after a 10-min walking exercise. Backpack carriage significantly reduced postural stability, whereas there was no significant effect under double pack loads. Distribution of heavy loads on the front-and-back is desirable for superior balance control.     

Algorithmically detectable directional changes in upper extremity motion indicate substantial myoelectric shoulder muscle fatigue during a repetitive manual task

Repetitive workplace tasks are associated with fatigue-induced changes to shoulder muscular strategies, potentially altering kinematics and elevating susceptibility to tissue overexposures. Accessible and reliable methods to detect shoulder muscle fatigue in the workplace are therefore valuable. Detectable changes in joint motion may provide a plausible fatigue identification method. In this investigation, the onset of the first kinematic changes, as identified by a symbolic motion representation (SMSR) algorithm, and the onset of substantial surface electromyography (sEMG) mean power frequency (MPF) fatigue were not significantly different, both occurring around 10% of task duration. This highlights the potential utility of SMSR identified directional changes in joint motion during repetitive tasks as a cue of substantial muscle fatigue, enabling ergonomics responses that can mitigate shoulder muscular fatigue accumulation and its associated deleterious physical effects.

Practitioner Summary: The onset of substantial muscle fatigue during a repetitive dynamic task was assessed using kinematics and myoelectric-based techniques. Algorithmically detectable directional changes in upper extremity joint motion occurred with the onset of substantial muscle fatigue, highlighting the potential of this as a useful approach for workplace fatigue identification.     

Office workers' computer use patterns are associated with workplace stressors

This field study examined associations between workplace stressors and office workers' computer use patterns. We collected keyboard and mouse activities of 93 office workers (68F, 25M) for approximately two work weeks. Linear regression analyses examined the associations between self-reported effort, reward, overcommitment, and perceived stress and software-recorded computer use duration, number of short and long computer breaks, and pace of input device usage. Daily duration of computer use was, on average, 30 min longer for workers with high compared to low levels of overcommitment and perceived stress. The number of short computer breaks (30 s–5 min long) was approximately 20% lower for those with high compared to low effort and for those with low compared to high reward. These outcomes support the hypothesis that office workers' computer use patterns vary across individuals with different levels of workplace stressors.     

Physical workload on neck and upper limb using two CAD applications

The aim was to evaluate (1) the physical workload on neck and upper limb in computer-aided design (CAD) work; (2) the impact of two applications (PROFESSIONAL-CADAM and PRO/Engineering) and (3) two input devices (computer mouse and keyboard), as well as (4) sitting and standing work positions. Fifteen CAD operators were interviewed and examined physically. For nine subjects, the physical workload was measured: electromyography (EMG) of trapezius and forearm extensor muscles, inclinometry of the head, the upper back and upper arms, as well as wrist goniometry. The muscular load was low in CAD work, but the inter-individual variation was considerable. Neither the positions were extreme, nor the movements. The applications, per se, did not have a large impact on the workload, but because of the need for different input devices the effect was strong. Using a keyboard meant higher angular velocities than using a mouse. Hence, when choosing a new software, which requires mainly a mouse as input device, this has to be balanced against the risk of disorders.     

The effect of police cruiser restraint cage configuration on shoulder discomfort,muscular demands,upper limb postures,and task performance during simulated police patrol

Advances in police-specific technology have led to changes in work layout and physical occupational demands of mobile police officers. This study investigated the influence of police cruiser compartment configuration on perceived discomfort, muscle activation, shoulder kinematics, and typing performance during simulated police patrol. Participants completed a one-hour session including simulated driving and 2-min typing trials in a standard compartment configuration with a fixed mobile data terminal (MDT) location (ST), and in a modified compartment configuration with an MDT in front of the user and a rearward translated seat (MOD). The MOD configuration resulted in reductions of 55–65% in perceived shoulder discomfort, up to 3.4% MVC in shoulder muscle demands, and more neutral humeral orientations (shoulder elevation reduced by 13–25°). These improvements associated with the MOD configuration may have ergonomic implications for future police car designs, particularly as new technology is introduced in the mobile environment and advanced solutions are sought.     

Effects of concurrent physical and mental demands for a short duration static task

The purpose of this study was to quantify the effects of concurrent physical and mental demands on the upper extremity muscle activity during static exertions. Seventeen healthy participants performed isometric upper extremity exertions at five levels of physical intensity (5%, 25%, 45%, 65%, and 85% maximum voluntary contraction (MVC)) in the presence and absence of a mental task (Stroop color word test). Muscular responses were quantified using surface electromyography (EMG) and motor performance was measured through force fluctuations. Subjective assessments were obtained through the NASA-TLX tool and the Borg CR-10 Scale. In general, a decrease in mean anterior and posterior deltoid muscle activity and co-contraction index (CCI) of the shoulder was observed in the presence of the mental task. However, these changes were more prominent at higher physical exertion levels compared to the lower levels. Furthermore, the additional mental task resulted in decreased upper and lower arm muscle activity, specifically at the 45% MVC level. Motor performance improved at the middle exertion levels, but was adversely affected by the mental task at higher exertion levels. Decreased motor performance at higher loads may have been a result of decreased muscular effort to maintain the loads in a steady posture. Both mental and physical demand adversely affected the NASA-TLX ratings, however, ratings using the Borg CR-10 Scale were only sensitive to changes in physical demand.

Relevance to industry

Workplace tasks, such as jobs performed by healthcare workers, assembly line workers, and computer operators, have become more multidimensional in the recent years; with workers experiencing combined physical and mental demands in their daily jobs, yet their effect on muscular responses is not clearly understood. Results from this study suggest that certain physical exertion levels are more susceptible to interference by mental demands than others.     

Musculoskeletal symptoms among mobile hand-held device users and their relationship to device use: A preliminary study in a Canadian university population

The study aims were, in a population of university students, staff, and faculty (n = 140), to: 1) determine the distribution of seven measures of mobile device use; 2) determine the distribution of musculoskeletal symptoms of the upper extremity, upper back and neck; and 3) assess the relationship between device use and symptoms. 137 of 140 participants (98%) reported using a mobile device. Most participants (84%) reported pain in at least one body part. Right hand pain was most common at the base of the thumb. Significant associations found included time spent internet browsing and pain in the base of the right thumb (odds ratio 2.21, 95% confidence interval 1.02–4.78), and total time spent using a mobile device and pain in the right shoulder (2.55, 1.25–5.21) and neck (2.72, 1.24–5.96). Although this research is preliminary, the observed associations, together with the rising use of these devices, raise concern for heavy users.     

人体下肢外骨骼机器人的发展及关键技术分析

下肢外骨骼机器人具有增强人体机能和辅助下肢康复训练的功能,在军事和医疗领域具有很好的发展前景,逐渐成为机器人领域的研究热点。本文分别介绍了增强人体机能的下肢外骨骼机器人和医疗下肢外骨骼机器人的国内外最新研究现状,概括并分析了与之相关的关键技术,探讨了下肢外骨骼机器人的今后发展方向。     

Wearing body armour and backpack loads increase the likelihood of expiratory flow limitation and respiratory muscle fatigue during marching

Abstract

The effect of load carriage on pulmonary function was investigated during a treadmill march of increasing intensity. 24 male infantry soldiers marched on six occasions wearing either: no load, 15?kg, 30?kg, 40?kg or 50?kg. Each loaded configuration included body armour which was worn as battle-fit or loose-fit (40?kg only). FVC and FEV₁ were reduced by 6 to 15% with load. Maximal mouth pressures were reduced post load carriage by up to 11% (inspiratory) and 17% (expiratory). Increased ventilatory demands associated with carrying increased mass were met by increases in breathing frequency (from 3 to 26 breaths·min^?1) with minimal changes to tidal volume. 72% of participants experienced expiratory flow limitation whilst wearing the heaviest load. Loosening the armour had minimal effects on pulmonary function. It was concluded that as mass and exercise intensity are increased, the degree of expiratory flow limitation also increases.

Practitioner Summary: This study investigated the effect of soldier load carriage on pulmonary function, to inform the trade-off between protection and burden. Load carriage caused an inefficient breathing pattern, respiratory muscle fatigue and expiratory flow limitation during marching. These effects were exacerbated by increases in mass carried and march intensity.     

The development and application of psychophysical methods in upper-extremity work tasks and task elements

This paper examines an approach to modeling the relationship between perceived acceptable work exposures and physical stressors in upper-extremity tasks using psychophysical methods. Several years of laboratory-based studies and results from a variety of simulated work tasks and task elements are summarized. The original impetus of these studies was founded in the pioneering work and successful application of psychophysical methods applied to manual materials handling tasks (e.g., lifting) generally beginning in the 1960s and 1970s. This approach provided unique and feasible solutions to work design problems involving exposure to the hazard of cumulative trauma. Presently, these methods were adapted to studying common upper-extremity tasks and task elements. Results provide conclusive evidence of the impact of required posture, force, gender and other variables on acceptable task frequency. These results and the psychophysical method in general, may be particularly helpful in establishing realistic and reasonable work design guidelines when workers are exposed to multiple, simultaneous hazards such as force, frequency, with deviated posture, etc, and in the absence of well-defined biomechanical or physiological-based models. Finally, a review of psychophysical theory and methods which can be applied to a wide range of occupational activities is provided.     

一种快速收敛的最大置信上界探索方法

深度强化学习(Deep Reinforcement Learning,DRL)方法在大状态空间控制任务上取得了出色效果,探索问题一直是该领域的一个研究热点.现有探索算法存在盲目探索、学习慢等问题.针对以上问题,提出了一种快速收敛的最大置信上界探索(Upper Confidence Bound Exploration w...