Dynamic loads on the upper extremities during two different floor cleaning methods

Characterization of upper limb use in health care workers during regular shifts: A quantitative approach based on wrist-worn accelerometers

Despite the high prevalence of upper limb (UL) work-related musculoskeletal disorders (WRMSD) among health care workers (HCWs), little is known about their relationship with exposure to biomechanical risk factors. This study aimed to assess UL activity features under actual working conditions using two wrist-worn accelerometers. Accelerometric data were processed to obtain duration, intensity, and asymmetry of UL use in 32 HCWs during the execution of commonly performed tasks (e.g., patient hygiene, transfer, and meal distribution) within a regular shift. The results show that such tasks are characterized by significantly different patterns of UL use, in particular, higher intensities and larger asymmetries were observed respectively for patient hygiene and meal distribution. The proposed approach appears, thus, suitable to discriminate tasks characterized by different UL motion patterns. Future studies could benefit from the integration of such measures with self-reported workers' perception to elucidate the relationship between dynamic UL movements and WRMSD.

Using the Rapid Upper Limb Assessment to examine the effect of the new Hotel Housekeeping California Standard

A housekeeper's job includes a variety of repetitive and strenuous tasks, which can put workers at high risk for musculoskeletal disorders. In 2018, a new standard was implemented in California aiming to prevent work-related injuries of hospitality industry workers. This paper assesses California housekeepers performing regular work tasks during their shifts from 2018 to 2020. Rapid Upper Limb Assessments (RULA) after the standard was implemented found average right-arm scores for scrubbing tasks (M = 6.93, SD = 0.00), vacuuming (M = 6.27, SD = 0.45), and trash-collecting (M = 4.48, SD = 0.50). Forces to move housekeeping carts were also evaluated, with 98% of pushing forces and 73% of turning forces observed within the accepted range. Results show that RULA scores remain high even after the implementation of the standard, with improvements only seen in tasks that required just changing of the method.

Effects of different tools and working height on physical workload in vertical cleaning tasks applying ambient control techniques

This study aimed to investigate the effects of different tools and working heights on physical workloads in vertical cleaning tasks. Thirty healthy adults were recruited to use a rag and a long-handle tool (LHT) to simulate cleaning operations on the Wii Fit board surfaces of 3 different heights, respectively. Participants used a lower 50th percentile force but were required to spend a longer time to finish the task while using an LHT than using a rag. The tool preferences were the main factors considered for efficiency and personal subjective workload and physiological load. 76.6% of the participants preferred to use the LHT instead of the rag at a high task height, but 70% preferred to use the rag when working at a medium task height. For low workload cleaning tasks on vertical surfaces, employers should provide cleaners with different handle lengths tools to choose from to reduce the cleaner's workload.

Which is the most ergonomic mop? A comparison of three domestic mopping systems

PURPOSE

To assess musculoskeletal risk factors (repetitions, posture, forces) of the upper limb during domestic floor mopping tasks.

METHODS

Two hundred women were surveyed to determine the most common mopping system, mopping patterns and type of flooring used in their homes. The biomechanical demands of the three most common mopping systems were then evaluated in the laboratory. Participants were also asked to rate their perceived levels of exertion and cleanliness of each mopping system.

RESULTS

The use of wet wipes had the highest repetition count and exertion rates during mopping and scrubbing tasks. Higher peak scrubbing forces were noted for the plunge mop. All participants found the cotton fibre mop to be the cleanest. All 3 mops had medium postural risk.

CONCLUSION

The advantages and disadvantages of each mopping system were outlined and may be used by occupational therapists when providing ergonomic advice to patients with upper limb musculoskeletal conditions.

The elixir of muscle activity and kinesiology in a health perspective: Evidence of worksite tailored exercise training alleviating muscle disorders

Physical activity is known to benefit health while muscle activation and movements performed during occupational work in contrast may result in work-related musculoskeletal disorders. Therefore, we posed the research question: which mode of muscle activation may result in a reversal of work-related disorders? To address this, we performed electromyographic (EMG) and kinematic assessments of workers with diverse exposure categories: sedentary monotonous work, prolonged walking/standing, and physically heavy work. The various job-specific exposure variables could be categorized in terms of duration, intensity, repetition, static component, peak force etc. that were subsequently identified as risk factors. Based on sports science principles we developed tailored exercise programs to counteract job exposure. EMG activity during exercise training was monitored to identify principal differences between exercise training and job patterns. Evidence from more than 20 RCT studies including >4000 workers showed positive effects such as decreased muscle pain and increased workability. Finally, we identified plausible underlying mechanisms in muscle tissue - human and animal - that confirmed metabolic, morphological, and hormonal changes with e.g. repetitive work that were reversal to adaptations reported with exercise training. Progress has been made in developing intelligent physical exercise training, IPET, as the best complementary activity to job exposure and includes muscle activations and movements that limit work-related inactivity atrophy as well as overload injury.

Wearable Monitoring Devices for Biomechanical Risk Assessment at Work: Current Status and Future Challenges-A Systematic Review

Background: In order to reduce the risk of work-related musculoskeletal disorders (WMSDs) several methods have been developed, accepted by the international literature and used in the workplace. The purpose of this systematic review was to describe recent implementations of wearable sensors for quantitative instrumental-based biomechanical risk assessments in prevention of WMSDs. Methods: Articles written until 7 May 2018 were selected from PubMed, Scopus, Google Scholar and Web of Science using specific keywords. Results: Instrumental approaches based on inertial measurement units and sEMG sensors have been used for direct evaluations to classify lifting tasks into low and high risk categories. Wearable sensors have also been used for direct instrumental evaluations in handling of low loads at high frequency activities by using the local myoelectric manifestation of muscle fatigue estimation. In the field of the rating of standard methods, on-body wireless sensors network-based approaches for real-time ergonomic assessment in industrial manufacturing have been proposed. Conclusions: Few studies foresee the use of wearable technologies for biomechanical risk assessment although the requirement to obtain increasingly quantitative evaluations, the recent miniaturization process and the need to follow a constantly evolving manual handling scenario is prompting their use.

Effects of work surface and task difficulty on neck-shoulder posture and trapezius activity during a simulated mouse task

OBJECTIVES

The purpose of this study is to evaluate the influence of the work surface and task difficulty on the head, upper back and upper arm postures and activity of the descending trapezius during a simulated mouse task.

METHODS

Healthy female university students (N = 15) were evaluated. The work surface was positioned at elbow height (EH) and above elbow height (AEH) and the task difficulty was set at low (LD) and high (HD) levels. The postures were recorded by inclinometers. Trapezius activity was normalized by the maximum voluntary isometric contraction (MVIC).

RESULTS

Significantly higher head flexion was found at EH compared to the AEH condition, with an average difference of 2°-5° at the same difficulty level. The HD task significantly increased head (3°-6°) and upper back flexion (6°-7°) at the same table height. For upper arm elevation and trapezius activation, the AEH condition presented higher upper arm elevation (about 6°-8°) and trapezius activity (0.8-1.4% of MVIC), regardless of the difficulty level of the task.

CONCLUSIONS

Head posture was influenced by the table height and task difficulty; the upper back posture by high difficulty; and upper arm posture and trapezius activity were only influenced by table height.

Effects of mop handle height on shoulder muscle activity and perceived exertion during floor mopping using a figure eight method

The aim of this study was to investigate effects of mop handle height on electromyographic (EMG) activities of the shoulder muscles and perceived exertion for the shoulder area during floor mopping using a figure eight method. An experimental study with 13 cleaners was conducted using surface EMG and category ratio (CR-10) scale. EMG activity was recorded unilaterally from the upper trapezius, infraspinatus, anterior and middle deltoid muscles. Each subject performed four trials of mopping and each trial consisted of using a different mop handle height (mop adjustment at the level of shoulder, chin, nose and eye) in randomized order. EMG data were normalized to a percentage of maximal voluntary contraction (%MVC). The muscle activities were assessed by estimating the 10th, 50th and 90th percentiles of the amplitude probability distribution function (APDF) of the EMG signals and analysed by linear mixed model analysis. Results showed that shoulder muscle activity was significantly lower when the mop handle height was adjusted to shoulder level or chin level as compared to eye level. These findings were supported by subjective ratings of exertion. It seems that mop handle height adjustment between shoulder and chin level may be recommended as a basis for figure eight mopping.

Cardiorespiratory fitness, cardiovascular workload and risk factors among cleaners; a cluster randomized worksite intervention

Background

Prevalence of cardiovascular risk factors is unevenly distributed among occupational groups. The working environment, as well as lifestyle and socioeconomic status contribute to the disparity and variation in prevalence of these risk factors. High physical work demands have been shown to increase the risk for cardiovascular disease and mortality, contrary to leisure time physical activity. High physical work demands in combination with a low cardiorespiratory fitness infer a high relative workload and an excessive risk for cardiovascular mortality. Therefore, the aim of this study is to examine whether a worksite aerobic exercise intervention will reduce the relative workload and cardiovascular risk factors by an increased cardiorespiratory fitness.

Methods/design

A cluster-randomized controlled trial is performed to evaluate the effect of the worksite aerobic exercise intervention on cardiorespiratory fitness and cardiovascular risk factors among cleaners. Cleaners are eligible if they are employed ≥ 20 hours/week, at one of the enrolled companies. In the randomization, strata are formed according to the manager the participant reports to. The clusters will be balanced on the following criteria: Geographical work location, gender, age and seniority. Cleaners are randomized to either I) a reference group, receiving lectures concerning healthy living, or II) an intervention group, performing worksite aerobic exercise “60 min per week”. Data collection will be conducted at baseline, four months and 12 months after baseline, at the worksite during working hours. The data collection will consist of a questionnaire-based interview, physiological testing of health and capacity-related measures, and objective diurnal measures of heart rate, physical activity and blood pressure. Primary outcome is cardiorespiratory fitness.

Discussion

Information is lacking about whether an improved cardiorespiratory fitness will affect the cardiovascular health, and additionally decrease the objectively measured relative workload, in a population with high physical work demands. Previous intervention studies have lacked robust objective measurements of the relative workload and physical work demands. This study will monitor the relative workload and general physical activity before, during after the intervention, and contribute to the understanding of the previously observed opposing effects on cardiovascular health and mortality from occupational and leisure time physical activity.

Trial registration

The study is registered as ISRCTN86682076.

Assessment of the development and implementation of tools in contract cleaning

This paper illustrates and discusses problems with the implementation and use of ergonomic tools and techniques in the process of cleaning. Cleaning is an occupation with a high risk of developing work-related disorders. One high-strain task where recommended tools and techniques are difficult to apply is cleaning staircases. This study evaluated the muscular activity of cleaners while mopping staircases using two different mop handles and found that an easily adjustable mop handle can decrease a cleaner's physical load. The results also show that the implementation and contextualization of the mop are of great importance for how a mop is used. A more holistic approach is needed to improve the benefits of good tools and techniques in cleaning work. More research is needed on how workplace organization can be improved to support the implementation of strategies to increase the health of professional cleaners.

Do new wipe materials outperform traditional lead dust cleaning methods?

Government guidelines have traditionally recommended the use of wet mopping, sponging, or vacuuming for removal of lead-contaminated dust from hard surfaces in homes. The emergence of new technologies, such as the electrostatic dry cloth and wet disposable clothes used on mopheads, for removal of dust provides an opportunity to evaluate their ability to remove lead compared with more established methods. The purpose of this study was to determine if relative differences exist between two new and two older methods for removal of lead-contaminated dust (LCD) from three wood surfaces that were characterized by different roughness or texture. Standard leaded dust, <75 μm, was deposited by gravity onto the wood specimens. Specimens were cleaned using an automated device. Electrostatic dry cloths (dry Swiffer), wet Swiffer cloths, paper shop towels with non-ionic detergent, and vacuuming were used for cleaning LCD from the specimens. Lead analysis was by anodic stripping voltammetry. After the cleaning study was conducted, a study of the coefficient of friction was performed for each wipe material. Analysis of variance was used to evaluate the surface and cleaning methods. There were significant interactions between cleaning method and surface types, p = 0.007. Cleaning method was found be a significant factor in removal of lead, p <0.001, indicating that effectiveness of each cleaning methods is different. However, cleaning was not affected by types of surfaces. The coefficient of friction, significantly different among the three wipes, is likely to influence the cleaning action. Cleaning method appears to be more important than texture in LCD removal from hard surfaces. There are some small but important factors in cleaning LCD from hard surfaces, including the limits of a Swiffer mop to conform to curved surfaces and the efficiency of the wetted shop towel and vacuuming for cleaning all surface textures. The mean percentage reduction in lead dust achieved by the traditional methods (vacuuming and wet wiping) was greater and more consistent compared to the new methods (electrostatic dry cloth and wet Swiffer mop). Vacuuming and wet wiping achieved lead reductions of 92% ± 4% and 91%, ± 4%, respectively, while the electrostatic dry cloth and wet Swiffer mops achieved lead reductions of only 89 ± 8% and  81 ± 17%, respectively.

Risk of musculoskeletal injury among cleaners during vacuuming

This study aimed to examine the risk of work-related upper-limb musculoskeletal disorders in cleaning workers during the work task of vacuuming. In total, 24 cleaning workers were observed while they performed vacuum cleaning tasks in the normal course of their employment in government schools, hospitality and commercial office space sectors. Risk of upper-limb musculoskeletal disorders were rated using three observational assessment tools: Manual Task Risk Assessment (ManTRA); Quick Exposure Check (QEC); the Rapid Upper Limb Assessment (RULA). Mean results (e.g. ManTRA wrist/hand cumulative wrist score 18.67 ± 1.27, QEC neck score 13 ± 1.77, RULA score 6.54 ± 0.509) demonstrated that cleaning workers who perform the task of vacuum cleaning are at risk of work-related upper-limb musculoskeletal injury, regardless of whether they use a back-pack or canister machine. Government school cleaners experienced greater risk of work-related upper-limb musculoskeletal disorders than workers in either the hospitality or commercial office space sectors.

PRACTITIONER SUMMARY

Cleaning workers in Australia are mostly female, ageing and of non-English-speaking backgrounds and involved in repetitive manual tasks. Their occupation is low status. This research confirms that vacuuming tasks are a risk for cleaning workers and highlights the need for further research to improve conditions for these workers.

Análise por dinâmica inversa, um complemento da avaliação fisioterapêutica do ombro

O objetivo do estudo é caracterizar as forças em atuação na articulação do ombro durante o movimento de elevação do membro superior no plano escapular por meio do método de dinâmica inversa, aqui sugerido como um meio complementar da avaliação fisioterapêutica. Esse método permite determinar os picos de momento proximal resultante (MPR) e da força proximal resultante (FPR) do ombro durante o movimento, possibilitando assim a avaliação objetiva das cargas impostas à articulação. Participaram do estudo 21 indivíduos do sexo masculino, cuja movimentação do ombro foi analisada por videogrametria em três diferentes situações de carga: sem carga, com peso livre e com resistência elástica. Um modelo matemático tridimensional foi utilizado para o cálculo do MPR e da FPR, permitindo caracterizar a evolução dessas variáveis ao longo da elevação do membro superior nas três situações de carga nos eixos póstero-anterior, caudal-cranial e médio-lateral, determinando seus respectivos picos. O método da dinâmica inversa revelou-se capaz de fornecer informações objetivas sobre as cargas impostas à articulação do ombro nas diversas amplitudes e situações de carga do movimento estudado, podendo tais informações servir como uma base concreta no planejamento de um programa de reabilitação do ombro.

Quantifying tasks, ergonomic exposures and injury rates among school custodial workers

A job exposure matrix of ergonomics risk factors was constructed for school custodial workers in one large school district in the province of British Columbia using 100 h of 1-min fixed-interval observations, participatory worker consensus on task durations and existing employment and school characteristic data. Significant differences in ergonomics risk factors were found by tasks and occupations. Cleaning and moving furniture, handling garbage, cleaning washrooms and cleaning floors were associated with the most physical risks and the exposure was often higher during the summer vs. the school year. Injury rates over a 4-year period showed the custodian injury rate was four times higher than the overall injury rate across all occupations in the school district. Injury rates were significantly higher in the school year compared with summer (12.2 vs. 7.0 per 100 full-time equivalents per year, p < 0.05). Custodial workers represent a considerable proportion of the labour force and have high injury rates, yet ergonomic studies are disproportionately few. Previous studies that quantified risk factors in custodial workers tended to focus on a few tasks or specific risk factors. This study, using participatory ergonomics and observational methods, systematically quantifies the broad range of musculoskeletal risk factors across multiple tasks performed by custodial workers in schools, adding considerably to the methodological literature.

What characterizes cleaners sustaining good musculoskeletal health after years with physically heavy work?

OBJECTIVES

The aim of this case-control study was to investigate characteristics of cleaners with good musculoskeletal health after years with physically heavy work.

METHODS

One hundred and 41 female seniority cleaners participated. Twenty-five reported no musculoskeletal symptoms, whereas 83 reported severe symptoms in the low back, neck shoulders or upper limbs. The groups were of matching age, height, body weight and seniority (19 years). Muscular strength was recorded by isometric maximal voluntary contractions on a day without pain. Exposure to physical risk factors at work, psychosocial work factors, and leisure time physical activity were assessed by a postal questionnaire.

RESULTS

Cleaners with good musculoskeletal health were not reporting different exposure to physical risk factors at work or leisure time physical activity, but had higher muscular strength and reported higher influence at work than cleaners with severe symptoms.

CONCLUSIONS

These findings suggest that muscular strength and influence at work are of relevance for sustaining good musculoskeletal health in workers with physically heavy work.

Applications of biomechanics for prevention of work-related musculoskeletal disorders

This paper summarises applications of biomechanical principles and models in industry to control musculoskeletal disorders of the low back and upper extremity. Applications of 2-D and 3-D biomechanical models to estimate compressive force on the low back, the strength requirements of jobs, application of guidelines for overhead work and application of strain index and threshold limit value to address distal upper extremity musculoskeletal disorders are presented. Several case studies applied in the railroad industry, manufacturing, healthcare and warehousing are presented. Finally, future developments needed for improved biomechanical applications in industry are discussed. The information presented will be of value to practising ergonomists to recognise how biomechanics has played a significant role in identifying causes of musculoskeletal disorders and controlling them in the workplace. In particular, the information presented will help practising ergonomists with how physical stresses can be objectively quantified.

Differences in physical workload, psychosocial factors and musculoskeletal disorders between two groups of female hospital cleaners with two diverse organizational models

OBJECTIVES

To clarify if differences in the physical workload, the psychosocial factors and in musculoskeletal disorders can be attributed to work organizational factors.

METHODS

The physical workload (muscular activity of m. trapezius, positions and movements of the head, upper arms and wrists and heart rate) was assessed in 24 female hospital cleaners working in a traditional work organization (TO) and in 22 working in an extended one (i.e. with an enlarged work content and more responsibilities; EO). The psychosocial work environment was assessed as job demand, decision latitude and social support in 135 (TO) and 111 (EO) cleaners, and disorders of the neck and upper extremity by a physical examination.

RESULTS

The EO group was associated with lower physical workload, in terms of heart rate ratio (23 vs 32; P<0.001), head and upper arm positions and movements (right upper arm, 50th percentile, 35 degrees/s vs 71 degrees/s; P<0.001) and wrist movements (20 degrees/s vs 27 degrees/s; P=0.001), than the TO group. The EO group reported higher decision latitude and lower work demand than the TO one, while we found no difference in social support. The prevalence of complaints and diagnoses in neck/shoulders were lower in the EO group (diagnoses 35% vs 48%; P=0.04). Moreover, the prevalence of subjects with at least ten physical finding in elbows/hands was lower in the EO group (10 vs 29; P<0.001).

CONCLUSION

Hospital cleaners have a high prevalence of neck and upper limb disorders and a high physical workload. Comparing two groups of cleaners, with differences in the way of organizing the work, lower physical workload, more beneficial psychosocial factors and a better musculoskeletal health was found in the group with an extended organization. Hence, the differences found can be attributed to the organizational factors.

A memory-based model for planning target reach postures in the presence of obstructions

Existing posture prediction and motion simulation models generally lack the capability of simulating human obstruction avoidance during target reach. This compromises the utility of digital human models for ergonomics, as many design problems involve interactions between humans and obstructions. To address this problem, this paper presents a novel memory-based posture planning (MBPP) model, which plans reach postures that avoid obstructions. In this model, the task space is partitioned into small regions called cells. For a given human figure, each cell is linked to a memory that stores various alternative postures for reaching the cell. When a posture planning problem is given in terms of a target and an obstruction configuration, the model examines postures belonging to the relevant cell, selects collision-free ones and modifies them to exactly meet the hand target acquisition constraint. Simulation results showed that the MBPP model is capable of rapidly and robustly planning reach postures for various scenarios.

The relationship between shoulder torques and the perception of muscular effort in loaded reaches

The objective of this study was to define the quantitative relationship between external dynamic shoulder torques and calibrated perceived muscular effort levels for load delivery tasks, for application in job analyses. Subjects performed a series of loaded reaches and, following each exertion, rated their perceived shoulder muscular effort. Motion and task physical requirements data were processed with a biomechanical upper extremity model to calculate external dynamic shoulder torques. Calculated torque values were then statistically compared to reported calibrated perceived muscular effort scores. Individual subject torque profiles were significantly positively correlated with perceived effort scores (r2 = 0.45-0.77), with good population agreement (r2 = 0.50). The accuracy of the general regression model improved (r2 = 0.72) with inclusion of factors specific to task geometry and individual subjects. This suggests two major conclusions: 1) that the perception of muscular shoulder effort integrates several factors and this interplay should be considered when evaluating tasks for their impact on the shoulder region; 2) the torque/perception relationship may be usefully leveraged in job design and analysis.

Representing and identifying alternative movement techniques for goal-directed manual tasks

Differences in motion patterns subserving the same movement goal can be identified qualitatively. These alternatives, which may characterize 'movement techniques' (e.g., the stoop and the squat lifting technique), may be associated with significantly different biomechanical constraints and physiological responses. Despite the widely shared understanding of the significance of alternative movement techniques, quantitative representation and identification of movement techniques have received little attention, especially for three-dimensional whole-body motions. In an attempt to systematically differentiate movement techniques, this study introduces a quantitative index termed joint contribution vector (JCV) representing a motion in terms of contributions of individual joint degrees-of-freedom to the achievement of the task goal. Given a set of uncharacterized (unlabeled) motions represented by joint angle trajectories (motion capture data), the JCV and statistical clustering methods enable automated motion classification to uncover a taxonomy of alternative movement techniques. The results of our motion data analyses show that the JCV was able to characterize and discern stoop and squat lifting motions, and also to identify movement techniques for a three-dimensional, whole-body, one-handed load-transfer task. The JCV index would facilitate consideration of alternative movement techniques in a variety of applications, including work method comparison and selection, and human motion modeling and simulation.

Intramuscular pressure and EMG relate during static contractions but dissociate with movement and fatigue

Intramuscular pressure (IMP) and electromyography (EMG) mirror muscle force in the nonfatigued muscle during static contractions. The present study explores whether the constant IMP-EMG relationship with increased force may be extended to dynamic contractions and to fatigued muscle. IMP and EMG were recorded from shoulder muscles in three sessions: 1) brief static arm abductions at angles from 0 to 90°, with and without 1 kg in the hands; 2) dynamic arm abductions at angular velocities from 9 to 90°/s, with and without 1 kg in the hands; and 3) prolonged static arm abduction at 30° for 30 min followed by recovery. IMP and EMG increased in parallel with increasing shoulder torque during brief static tasks. During dynamic contractions, peak IMP and EMG increased to values higher than those during static contractions, and EMG, but not IMP, increased significantly with speed of abduction. In the nonfatigued supraspinatus muscle, a linear relationship was found between IMP and EMG; in contrast, during fatigue and recovery, significant timewise changes of the IMP-to-EMG ratio occurred. The results indicate that IMP should be included along with EMG when mechanical load sharing between muscles is evaluated during dynamic and fatiguing contractions.

Biomechanical model predicting electromyographic activity in three shoulder muscles from 3D kinematics and external forces during cleaning work

BACKGROUND

The shoulder region is a common site of work-related musculoskeletal disorders. Biomechanical models may reveal the relative importance of force, joint-moments, and angular velocity for predicting muscle activity, thereby contributing to identify risk factors.

OBJECTIVE

The aim of the present study was to predict muscle activity patterns from joint kinetics during cleaning work and to identify the most important variables requesting muscle activity.Design. A comparative study of six cleaners performing five different floor cleaning tasks (combinations of tool and working method) in a laboratory setting.

METHODS

Net forces and moments at the glenohumeral joint were estimated using a video-based 3D link segment model together with 3D force-transducers at each hand, separately. Angular velocities of the upper arm were calculated, and electromyographic activity was recorded bilaterally from the muscles trapezius, deltoideus, and infraspinatus.

RESULTS

The biomechanical model revealed abduction moment in the glenohumeral joint to be the most important factor for development of muscle activity in m. deltoideus and m. infraspinatus, while for m. trapezius vertical force was most important.

CONCLUSION

Muscle specific determinants for shoulder muscle activity could be identified from glenohumeral joint kinetics.

RELEVANCE

This study documents that mechanical work requirements in terms of joint forces, moments of force and angular velocities can predict major fractions of muscle activity patterns in the upper extremities. The biomechanical model used for this prediction revealed different factors of importance for individual muscles. This knowledge is fundamental for work place interventions aiming at minimizing overloading of specific muscles to prevent or rehabilitate muscle disorders.