Comparison of the observer, single-frame video and computer vision hand activity levels.

Observer, manual single-frame video, and automated computer vision measures of the Hand Activity Level (HAL) were compared. HAL can be measured three ways: (1) observer rating (HALO), (2) calculated from single-frame multimedia video task analysis for measuring frequency (F) and duty cycle (D) (HALF), or (3) from automated computer vision (HALC). This study analysed videos collected from three prospective cohort studies to ascertain HALO, HALF, and HALC for 419 industrial videos. Although the differences for the three methods were relatively small on average (<1), they were statistically significant (p < .001). A difference between the HALC and HALF ratings within ±1 point on the HAL scale was the most consistent, where more than two thirds (68%) of all the cases were within that range and had a linear regression through the mean coefficient of 1.03 (R2 = 0.89). The results suggest that the computer vision methodology yields comparable results as single-frame video analysis.Practitioner summary: The ACGIH Hand Activity Level (HAL) was obtained for 419 industrial tasks using three methods: observation, calculated using single-frame video analysis and computer vision. The computer vision methodology produced results that were comparable to single-frame video analysis.

Predicting Sagittal Plane Lifting Postures From Image Bounding Box Dimensions.

OBJECTIVE: A method for automatically classifying lifting postures from simple features in video recordings was developed and tested. We explored if an "elastic" rectangular bounding box, drawn tightly around the subject, can be used for classifying standing, stooping, and squatting at the lift origin and destination. BACKGROUND: Current marker-less video tracking methods depend on a priori skeletal human models, which are prone to error from poor illumination, obstructions, and difficulty placing cameras in the field. Robust computer vision algorithms based on spatiotemporal features were previously applied for evaluating repetitive motion tasks, exertion frequency, and duty cycle. METHODS: Mannequin poses were systematically generated using the Michigan 3DSSPP software for a wide range of hand locations and lifting postures. The stature-normalized height and width of a bounding box were measured in the sagittal plane and when rotated horizontally by 30°. After randomly ordering the data, a classification and regression tree algorithm was trained to classify the lifting postures. RESULTS: The resulting tree had four levels and four splits, misclassifying 0.36% training-set cases. The algorithm was tested using 30 video clips of industrial lifting tasks, misclassifying 3.33% test-set cases. The sensitivity and specificity, respectively, were 100.0% and 100.0% for squatting, 90.0% and 100.0% for stooping, and 100.0% and 95.0% for standing. CONCLUSIONS: The tree classification algorithm is capable of classifying lifting postures based only on dimensions of bounding boxes. APPLICATIONS: It is anticipated that this practical algorithm can be implemented on handheld devices such as a smartphone, making it readily accessible to practitioners.

An investigation into four different sit-stand workstation use schedules.

Twelve office workers participated in a study investigating effects of four sit/stand schedules (90-min sit/30-min stand, 80/40, 105/15, and 60/60) via several objective and subjective measures (muscle fatigue, foot swelling, spinal shrinkage, and self-reported discomfort). Results showed that there were no significant differences in shoulder and low back static muscle activities between sitting and standing. Muscle fatigue was developed during workday under all schedules. The longest standing schedule seemed to have a tendency of reducing muscle fatigue. None of the schedules helped or worsened foot swelling and spinal shrinkage. More active break-time activities seemed reducing muscle fatigue and foot swelling. While the self-reported bodily discomfort levels were generally low, the preferred schedules among the participants were varied, although the least standing schedule was the least preferred. We may conclude that effects of using sit-stand workstation to improve musculoskeletal health may be limited but promoting more active break-time activities can help. Practitioner Summary: Sit-stand workstations are used to reduce work-related musculoskeletal disorders. This study shows that office workers prefer sit/stand durations in the range between 1:1 and 3:1. Longer standing may have the potential to reduce muscle fatigue. However, active break-time activities may be more effective in reducing muscle fatigue and foot swelling.

Normative data on the one-handed static pull strength of a Chinese population and a comparison with American data.

We assess the one-handed static pull strength of a Chinese population and compare it to that of an American sample. Fifty men and 50 women in five age groups were asked to exert their maximum one-handed pull strength in three pulling directions (across, front and side) and from four pulling heights (61 cm, 76 cm, waist height and above-shoulder height). The results showed that women had less pull strength than men under all of the conditions tested. The front and side pulling resulted in the greatest pull strength, with a decrease detected when the pulling height was increased. The American sample exhibited greater strength than the Chinese. Body mass and men's handgrip force were also associated with the pull strength. These variables should be taken into account in the development of tasks related to one-handed pulling. Practitioner summary: In this paper, we report a laboratory-based experiment conducted to assess the one-handed static pull strength of a Chinese population and compare the results with those of an American population. The variables associated with pull strength included gender, pulling direction, pulling height, race, body mass and men's handgrip force.

Synthesis of novel lipophilic N-substituted norcantharimide derivatives and evaluation of their anticancer activities.

This research attempted to study the effect of lipophilicity on the anticancer activity of N-substituted norcantharimide derivatives. Twenty-three compounds were synthesized and their cytotoxicities against five human cancer cell lines studied. The lipophilicity of each derivative was altered by its substituent, an alkyl, alkyloxy, terpenyl or terpenyloxy group at the N-position of norcantharimide. Further, among all synthesized derivatives studied, the compounds N-farnesyloxy-7-oxabicyclo[2.2.1]heptane-2,3-dicarboximide (9), and N-farnesyl-7-oxabicyclo[2.2.1]heptane-2,3-dicarboximide (18), have shown the highest cytotoxicity, anti-proliferative and apoptotic effect against human liver carcinoma HepG2 cell lines, yet displayed no significant cytotoxic effect on normal murine embryonic liver BNL CL.2 cells. Their overall performance led us to believe that these two compounds might be potential candidates for anticancer drugs development.

Shoulder muscle fatigue development in young and older female adults during a repetitive manual task.

Age may modify the association between occupational physical demand and muscle loading, and ultimately increase the risk of musculoskeletal disorders. The goal of this study was to investigate age-related differences in shoulder muscle fatigue development during a repetitive manual task. Twenty participants in two age groups completed an 80-minute simulated low-intensity assembly task. Electromyographic (EMG) manifestation of muscle fatigue was observed in the upper trapezius, deltoid and infraspinatus muscles in both age groups, and coincided with an increase in the subjective ratings of perceived exertions. Compared with the younger group, older group showed a more monotonic decrease in EMG power frequency in the upper trapezius and deltoid muscles. However, the age-related difference in EMG amplitude was less consistent. Relative rest time of the upper trapezius muscle in the older group was less than the young group throughout the task. The observed patterns of EMG measures suggest that older participants may have disadvantages in fatigue resistance in the upper trapezius and posterior deltoid muscles during the simulated repetitive manual task.

A year-long case study of multicomponent interventions to promote physical activity in office workers: A randomized control trial.

The purpose of this study was to identify if workplace interventions, (i.e., mindfulness classes and monetary incentives for gym attendance), influenced workers' physical activity. Office-based participants were randomized into one of four intervention assignments: 1) CONTROL (no interventions) (n = 40), 2) MINDFULNESS (n = 33), 3) GYM INCENTIVE (n = 41), or 4) BOTH mindfulness and gym incentive (n = 31). Activity-tracker and self-reported metabolic expenditure and step counts were gathered between January 2020 and December 2020 whereas the eight-week long interventions were provided between January and March 2020, when the impact of COVID-19 pandemic started. While physical activity decreased during the follow-up months, percent changes of physical activity at 1-, 2-, and 9-month follow-ups compared to baseline show no significant differences between or across the four intervention assignments (p > 0.05). These results suggest that the intervention assignments had no effect on physical activity from baseline. The lack of effectiveness of these interventions on participant physical activity could be attributed to the influence of the COVID-19 pandemic, and any effects of the interventions could not outweigh the effects of the pandemic.

Work from home: Facilitators for an effective ergonomic work system.

Previous studies on Human Factors and Ergonomics (HFE) have primarily examined the impact of Work-From-Home (WFH) on worker health and well-being, yet little research has examined the optimal implementation process of WFH programs. Work systems perspective suggests that organizational policies, leadership, and psychological factors collectively influence the success of organizational change efforts. Our study explored the roles of managerial/supervisory, psychological, and organizational policy factors in facilitating the relationship between employees' HFE awareness and their acceptance and satisfaction with the WFH arrangement. Using data from 3195 knowledge workers in the US who use computers as their primary work tool and have worked from home at least one day in the past 30 days, we employed structural equation modeling to test our hypotheses. Transformational HFE leadership and employees' general self-efficacy are pivotal in implementing ergonomic WFH arrangements. The combination of employees' HFE awareness, transformational HFE leadership, and adequate levels of self-efficacy may foster positive process outcomes (e.g., readiness for WFH arrangement, workspace design satisfaction) in WFH arrangements. Efforts that are coordinated across organizational levels determine the effectiveness of organizational change.

Effect of aging on inter-joint synergies during machine-paced assembly tasks.

In recent years, uncontrolled manifold (UCM) analysis has emerged as an important method to study variability of human movements. The current study investigated the upper extremity movements during typical assembly tasks using the framework of the UCM analysis. Younger and older participants performed machine-paced assembly tasks, while the kinematics of upper extremities were recorded using a motion tracking system. The upper extremity was modeled as a 7 degrees-of-freedom system. The variance of joint angles within the UCM space (V UCM) and the variance perpendicular to the UCM space (V ORT) were analyzed. The results indicated that V UCM were not significantly different for the older and younger groups. For the older group, V ORT was significantly less than the younger group and resulted in less total variance (V TOT) and a better synergy level (Z ΔV ). Therefore, the synergies of upper extremity movement may not be impaired for machine-paced tasks as people age. While current results showed a different effect of aging on the synergies of body movement compared with one previous study, they were in line with a recently proposed theory that for natural tasks, aging people did not have impairment in the ability to organize upper extremity movement into synergies.

Shoulder joint loading and posture during medicine cart pushing task.

Excessive physical loads and awkward shoulder postures during pushing and pulling are risk factors for shoulder pain. Pushing a medicine cart is a major component of a work shift for nurses and medical assistants in hospitals and other health care facilities. A laboratory experiment was conducted to examine the effects of common factors (e.g., lane congestion, cart load stability, floor surface friction) on shoulder joint moment and shoulder elevation angle of participants during cart pushing. Participants pushed a medicine cart on straight tracks and turning around right-angle corners. Peak shoulder joint moments reached 25.1 Nm, 20.3 Nm, and 26.8 Nm for initial, transition, and turning phases of the pushing tasks, indicating that shoulder joint loading while pushing a medical cart is comparable to levels previously reported from heavy manual activities encountered in industry (e.g., garbage collection). Also, except for user experience, all other main study factors, including congestion level, cart load stability, location of transition strip, shoulder tendency, surface friction, and handedness, significantly influenced shoulder joint moment and shoulder elevation angle. The findings provide a better understanding of shoulder exposures associated with medicine cart operations and may be helpful in designing and optimizing the physical environment where medicine carts are used.

The natural angle between the hand and handle and the effect of handle orientation on wrist radial/ulnar deviation during maximal push exertions.

The purpose of this experiment was to quantify the natural angle between the hand and a handle, and to investigate three design factors: handle rotation, handle tilt and between-handle width on the natural angle as well as resultant wrist radial/ulnar deviation ('RUD') for pushing tasks. Photographs taken of the right upper limb of 31 participants (14 women and 17 men) performing maximal seated push exertions on different handles were analysed. Natural hand/handle angle and RUD were assessed. It was found that all of the three design factors significantly affected natural handle angle and wrist RUD, but participant gender did not. The natural angle between the hand and the cylindrical handle was 65 ± 7°. Wrist deviation was reduced for handles that were rotated 0° (horizontal) and at the narrow width (31 cm). Handles that were tilted forward 15° reduced radial deviation consistently (12-13°) across handle conditions. PRACTITIONER SUMMARY: Manual materials handling (MMH) tasks involving pushing have been related to increased risk of musculoskeletal injury. This study shows that handle orientation influences hand and wrist posture during pushing, and suggests that the design of push handles on carts and other MMH aids can be improved by adjusting their orientation to fit the natural interface between the hand and handle.

Physiological responses, trunk posture, and work pace in commercial building cleaning in Washington State: An observational field study.

INTRODUCTION: This study aimed to investigate whether work pace is a critical indicator for predicting a janitor's risk of work-related musculoskeletal disorders (WMSDs). METHOD: Field measurements were obtained from commercial building janitors as well as the determination of work pace. Physiological responses collected were heart rate, energy expenditure (calories), activity level (METs), steps, trunk posture. Data were obtained using direct measurements, along with a time study, which was performed by shadowing 13 janitors in Washington State. The measured values were summarized descriptively, and five of the most common janitorial tasks were compared. The relationships between work pace and the physiological response variables were determined by calculating the Pearson product-moment correlation coefficients. RESULTS: The highest average percent heart rate reserve (47.4%) was reported during restroom cleaning, while the highest activity and energy expenditure levels (3.6 METs and 217.1 calories/h) were reported for mopping. The top 90% of trunk flexion angles and the highest percentage of time in trunk flexion from 20° to 60° were recorded during restroom cleaning. Restroom cleaning showed the highest correlation between all the physiological response variables and work pace. In most of the tasks, a high work pace may have increased the degree and duration of severe trunk flexion. CONCLUSION: Overall, when several tasks were considered, the extent of physiological responses, trunk joint angles, and exposure time to awkward postures tended to increase with an increase in work pace. PRACTICAL APPLICATIONS: This study showed the feasibility of using the work pace measured from time studies as a predictive indicator of WMSDs risks. Using this information, managers may compose a schedule that can minimize WMSDs risks while considering actual work pace deviations that may impact a janitor's ability to complete assigned tasks properly within a shift.

The effects of joint torque, pace and work:rest ratio on powered hand tool operations.

Repetitive use of hand-held power tools is associated with work-related upper extremity musculoskeletal disorders. Using a pneumatic nutrunner, 21 men completed twelve 360 repetitive fastener-driving sessions on three joints (hard, soft and control) at slow and fast pace, and two different work:rest patterns. Handgrip force and perceived exertions were collected throughout each session. For the control joint, the mean grip force exerted was 39.6% of maximum voluntary exertion (MVE) whereas during hard and soft joint sessions it was 48.9% MVE and 56.9% MVE, respectively. Throughout each session, the grip force decreased, more while operating soft and hard joints as compared with the control joint (regression slope: -0.022 and -0.023, compared with -0.007 N/drive, respectively), suggesting considerable upper extremity muscular effort by participants during torque buildup. Fast work pace resulted in higher average grip forces by participants but a greater decrease in the force as the session progressed. Providing rest breaks reduced perceived exertions. The findings gain additional knowledge for assembly task design to possibly reduce the hand/arm injury risks for the operator. Practitioner Summary: Powered hand tools are widely used in assembly and manufacturing industries. However, the nature of their repetitive use on human operator biomechanical and perceptual responses is not fully understood. This study examined work-related risk factors such as joint torque, pace and work:rest ratios on powered hand tool performance.

Physical activity changes among office workers during the COVID-19 pandemic lockdown and the agreement between objective and subjective physical activity metrics.

After the onset of the COVID-19 pandemic, many office workers transitioned to working-from-home (WFH) which altered routine physical activity (PA). To understand how these workers' PA were affected throughout the pandemic, PA data collected in January, April, June, and December 2020 with an activity tracker and a validated survey were analyzed. Between January and December, it was found that step counts during the weekday decreased (p < 0.01), weekday heart rate was higher than weekends (p < 0.01), activity-tracker and self-reported PA decreased (p < 0.01), and sitting time increased (p < 0.01). To understand the agreement between the objective and subjective METs, Bland-Altman analyses were completed and demonstrated an acceptable level of agreement. Findings show decreased level of PA amongst WFH office workers and that the activity tracker and survey are reliable methods of recording WFH PA.

Cleaning in the 21st Century: The musculoskeletal disorders associated with the centuries-old occupation - A literature review.

Workers performing cleaning duties experience higher injury rates, especially in the form of musculoskeletal disorders (MSDs), than other industries. It is essential to understand the inherent risks associated with the nature of this occupation. Based on the Balance Theory (Smith & Carayon-Sainfort, 1989), this review surveys the current literature, especially those published since the previous review paper (Kumar & Kumar, 2008), and identifies which elements contributing to MSD risks were examined: task, technology, organization, environment, individual, and their interactions. Thirty-nine research papers published between 2005 and 2021 are identified and summarized. Among these papers, task and individual elements received the most attention, at 42 and 34 occurrences, respectively. The interaction elements of technology-organization, technology-environment, and organization-environment received less than three mentions. The goal of this literature review is to update the knowledge base and identify current trends for the cleaning occupation. Possible interventions for risk reduction and future research directions are suggested.

The job demand-control-support model and work-related musculoskeletal complaints in daytime and nighttime janitors: The mediating effect of burnout.

Janitors' jobs require repetitive work with low control (skill discretion, decision authority) and social support. Previous studies have found this constellation of work conditions leads to high stress levels. This study investigated the relationships among job demand-control-support, burnout, and musculoskeletal symptoms for commercial janitors in Washington State. Structural equation modeling was performed using data from 208 participants with analyses comparing models of daytime and nighttime janitors. Burnout fully mediated the relationship between job demands and musculoskeletal complaints among daytime janitors. Among nighttime janitors, burnout mediated between job demands, job control, and social support, and musculoskeletal complaints. The nighttime janitors' model was more fully supported compared to the daytime model. This study is one of a small number that examine and bring attention to the importance of janitors' burnout. Recommendations to improve the psychosocial work environment toward mitigating burnout and reducing musculoskeletal complaints are provided.

Factors Affecting Material-Cart Handling in the Roofing Industry: Evidence for Administrative Controls.

Material-cart handling can be strenuous and lead to overexertion injuries. The aim of this study is to produce a thorough understanding of how the cart condition, tire type, physical environment-related factors, and load interact to influence the ergonomics and productivity of cart handling. Eighteen roofing carts with different conditions, tires, and loads were tested by one subject on three laboratory tracks: one L-shaped, one with ramps within constrained spaces, and one with obstacles within constrained spaces. A multiple linear regression analysis was performed to quantify the main and interaction effects of the factors of interest on the cart operations. The research findings confirm that using aged carts increases the injury risk by as much as 30.5% and decreases productivity by 35.4%. Our study also highlights the necessity of keeping an open space for cart operation; the travel distance from a cart to a ramp/obstacle should be greater than 61 cm. Finally, the results suggest the at-risk thresholds for different ramp slopes and obstacle heights, and the safe load capacities for the various working circumstances that are common on construction sites. The evidence created in this study can be translated into administrative controls for cart handling to reduce overexertion injuries and enhance performance.

Activation patterns of shoulder internal and external rotators during pure axial moment generation across a postural range.

Musculoskeletal risk is mediated by body posture, especially for static tasks. Workstations that require non-neutral postures can lead to increased load, muscular fatigue and injury risk. However, demands during simple axial rotation tasks are not well-defined. The purpose of this study is to quantify the muscular activity of during static axial rotation in a range of postures. Eighteen participants performed 76 axial rotation exertions in varying combinations of humeral elevation angles (30°-60°-90°-120°-150°), plane of elevation (30°-60°-90°-120°) and exertion intensity (20-40%). Six unilateral (right) muscles (pectoralis major (clavicular and sternal), posterior deltoid, teres major, infraspinatus, latissiumus dorsi) were monitored using surface electromyography (EMG). EMG was normalized and integrated over 2 s. The influences of elevation, plane, and intensity on activity levels were then tested with a 3-way ANOVAs (p < .05). During internal rotation, activity was highest at low elevation/high plane combinations for the internal rotators, but at high elevation/low plane combinations for the external rotators. During the 40% intensity exertions, activity levels were highest at lower elevations for internal rotator but at high elevations for the external rotators. During external rotation, as the degree of elevation increased, the activity of the external rotator muscles also increased while internal rotators were unaffected. Humeral muscles responsible for axial rotation are influenced by arm posture during axial rotation exertions. High elevation and plane combinations resulted in high demands for external rotator muscles and this should be considered for job design and injury risk.

Simple benchmarking method for determining the accuracy of depth cameras in body landmark location estimation: Static upright posture as a measurement example.

To evaluate the postures in ergonomics applications, studies have proposed the use of low-cost, marker-less, and portable depth camera-based motion tracking systems (DCMTSs) as a potential alternative to conventional marker-based motion tracking systems (MMTSs). However, a simple but systematic method for examining the estimation errors of various DCMTSs is lacking. This paper proposes a benchmarking method for assessing the estimation accuracy of depth cameras for full-body landmark location estimation. A novel alignment board was fabricated to align the coordinate systems of the DCMTSs and MMTSs. The data from an MMTS were used as a reference to quantify the error of using a DCMTS to identify target locations in a 3-D space. To demonstrate the proposed method, the full-body landmark location tracking errors were evaluated for a static upright posture using two different DCMTSs. For each landmark, we compared each DCMTS (Kinect system and RealSense system) with an MMTS by calculating the Euclidean distances between symmetrical landmarks. The evaluation trials were performed twice. The agreement between the tracking errors of the two evaluation trials was assessed using intraclass correlation coefficient (ICC). The results indicate that the proposed method can effectively assess the tracking performance of DCMTSs. The average errors (standard deviation) for the Kinect system and RealSense system were 2.80 (1.03) cm and 5.14 (1.49) cm, respectively. The highest average error values were observed in the depth orientation for both DCMTSs. The proposed method achieved high reliability with ICCs of 0.97 and 0.92 for the Kinect system and RealSense system, respectively.

Exposures and physiological responses in power tool operations: fastening vs. unfastening threaded hardware.

Powered hand tools have the potential to produce reaction forces that may be associated with upper extremity musculoskeletal disorders. This study examined and compared the kinetic and physiological impacts on operator upper extremities between the fastening and unfastening operations. Thirty-two healthy, right-handed male operators used four tools on two joint simulators at different working heights and distances in the laboratory. Three work configurations were simulated: pistol grip tools on a vertical and horizontal surface, and right angle tools on a horizontal surface. Grip force was measured on an instrumented handle attached to each tool. Muscle activity was monitored at the wrist flexor and extensor and the upper trapezius of the right arm. Paired comparisons showed that when pistol grip tools were used, the peak torque to unfasten a joint (3.7 Nm) was significantly less than to fasten the same joint (5.7 Nm). However, the exposure time was longer for unfastening cycles (98 ms more on the horizontal surface, and 107 ms more on the vertical surface). The average grip force scaled to corresponding peak tool torque revealed that the effort to react against torque was greater in unfastening cycles than in fastening cycles for all work configurations. It also showed that as a proximal stabilizer, the upper trapezius muscle had a greater activity in unfastening cycles. The kinetic and physiological responses demonstrated that unfastening fasteners, which has been neglected in the literature, have the potential to increase risk for musculoskeletal disorders and should be considered in ergonomics assessment in the workplace.