Browsing by Author "Srinivasan, Divya"

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    Applications of Motor Variability for Assessing Repetitive Occupational Tasks
    Sedighi, Alireza (Virginia Tech, 2017-06-07)
    The human body has substantial kinetic and kinematic degrees-of-freedoms, so redundant solutions are available for the central nervous system (CNS) to perform a repetitive task. Due to these redundancies, inherent variations exist in human movement, called motor variability (MV). Current evidence suggests that MV can be beneficial, and that there is an inverse association between MV and risk of injury. To better understand how the CNS manipulates MV to reduce injury risks, we investigated the effects of individual differences, task-relevant aspects, and psychological factors as modifiers of MV. Earlier work found that experienced workers adapted more stable movements than novices in repetitive lifting tasks. To expand on this, we quantified how MV differs between experienced workers and novices in different lifting conditions (i.e., lifting asymmetry and fatigue). Three different measures (cycle-to-cycle SD, sample entropy, and the goal equivalent manifold) were used to quantify MV. In a symmetric lifting task, experienced workers had more constrained movement than novices, and experienced workers exhibited more consistent behavior in the asymmetric condition. Novices constrained their movements, and could not maintain the same level of variability in the asymmetric condition. We concluded that experienced workers adapt stable or flexible strategies depending on task difficulty. In a prolonged lifting task, both groups increased their MV to adapt to fatigue; they particularly increased variability in a direction that had no effects on their main task goal. Developing fatigue also makes it difficult for individuals maintain the main goal. Based on these results, we conclude that increasing variability is an adaptive strategy in response to fatigue. We also assessed variability in gait parameters to compare gait adaptability using a head-worn display (HWD) compared with head-down displays for visual information presentation. An effective strategy we observed for performing a cognitive task successfully during walking was to increase gait variability in the goal direction. In addition, we found that head-up walking had smaller effects on MV, suggesting that HWDs are a promising technology to reduce adverse events during gait (e.g., falls). In summary, these results suggest that MV can be a useful indicator for evaluating some occupational injury risks.
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    Assessing the Effects of Exoskeleton Use on Balance and Postural Stability
    Park, Jangho (Virginia Tech, 2021-09-30)
    There is emerging evidence for the potential of occupational back-support exoskeletons (BSEs) to reduce physical demands, and thereby help control/prevent the risk of overexertion injuries associated with manual material handling. However, it is important to understand whether BSEs also introduce any unintended safety challenges. One potential risk associated with BSE use is increased risk of falls, since their extra weight, rigid structure, and external hip extension torque may increase demands on the postural control system. However, there is currently limited evidence on whether, and to what extent, BSE use alters postural stability and/or fall risk. The primary goal of this work was to understand the effects of exoskeleton use, and quantify the effects of exoskeleton design parameters, on balance and postural stability, with a focus on passive BSEs used for repetitive lifting work. A comprehensive evaluation of BSE use was performed under controlled laboratory conditions, focusing on three classes of human activity that form the basis of maintaining postural balance in diverse real-life scenarios: maintenance of a specified posture, voluntary movement, and reaction to an external perturbation. The first study demonstrated that during quiet bipedal stance, BSE use increased median frequency and velocity of the center of pressure in the anterior-posterior direction. In the second study on level walking, BSE use caused an increase in gait step width and gait variability, and decrease in the margin of stability. BSE use with high supportive torque led to adapted gait patterns in early-stance phase. Hip range of motion and peak hip flexion velocity also decreased, and participants exhibited different strategies to increase mechanical energy for propelling the leg in late-stance phase: these effects increased with increasing torque applied by the exoskeleton. In the final study, BSE use did not alter the maximal lean angle from which individuals could successfully execute single step balance recovery, following a forward loss of balance. However, several recovery responses were negatively affected by BSE use, including increased reaction time, impeded hip flexion, and reduced margin of stability in the high-torque condition. This is the first systematical investigation to quantify the effects of passive BSEs with multiple supportive torque levels on balance and postural stability. While exoskeleton effects on static balance were minimal, more substantial changes in gait spatiotemporal parameters, hip joint kinematics, and dynamic margins of stability were observed in the later studies. Our results indicate that postural stability deteriorated with exoskeleton use in dynamic conditions, and provide mechanistic insight into how stability is altered by different exoskeleton design factors such as added mass, restricted range of motion, and external hip extension torque. While our results are suggestive of increased fall risk, especially in the high-torque condition, fall risk in real life is moderated by a complex combination of individual and environmental conditions. Future work should consider more complex, realistic tasks and also include a more diverse sample that is studied under longer exposure durations, to further elucidate these findings. Our characterizations of a wide variety of postural responses as a function of exoskeleton torque settings are expected to contribute to improving both design and practice guidelines to facilitate the safe adoption of BSEs in the workplace.
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    Assessing the Relationship between Occupational Injury Risk and Performance: the Efficacy of Adding Adjustability and Using Exoskeletons in the Context of a Simulated Drilling Task
    Alabdulkarim, Saad A. (Virginia Tech, 2017-11-16)
    Work-related musculoskeletal disorders (WMSDs) continue to occur despite an increasing understanding of the risk factors that initiate these disorders. Ergonomics is commonly seen as a health and safety approach that has no influence on performance, a perspective potentially hindering intervention proposals in practice. Highlighting potential performance benefits can facilitate intervention cost-justification, along with the traditional focus on reducing exposure to injury risk. The main objective of this research was to examine the dual influences (i.e., on performance and injury risk) of two distinct types of interventions: adding adjustability, as a commonly advocated approach when considering ergonomics early in the (re)design phase to change task demands; and using exoskeletons to enhance worker capacity. A simulated drilling task was used, which was considered informative as it entailed diverse demands (precision, strength, and speed) and permitted quantifying two dimensions of task performance (productivity and quality). The dual influences of three levels of workstation adjustability were examined first; increasing adjustability improved performance, with this benefit occurring only when a given level of adjustability also succeeded in reducing ergonomic risk. Across examined conditions, several significant linear associations were found between risk (e.g., Strain Index score) and performance metrics (e.g., completion time), further supporting an inverse relationship between these two outcomes. The dual influences of three distinct passive exoskeletal designs were investigated/compared subsequently, in a simulated overhead drilling task and considering the potential moderating effects of tool mass and precision requirements. Specific designs were: full-body (Full) and upper-body (Arm) exoskeletons with attached mechanical arms; and an upper-body (Shl) exoskeleton providing primarily shoulder support. Both designs with mechanical arms increased static and median total muscle activity while deteriorating quality. The Shl design reduced shoulder loading while increasing dominant upper arm loading and deteriorating quality in the highest precision requirements. Influences of both increasing precision and tool mass were fairly consistent across the examined designs. As such, no single design was obviously superior in both physical demands and performance. Although future work is needed under more diverse/realistic scenarios, these results may be helpful to (re)design interventions that achieve dual benefits on performance and injury risks.
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    Assessment of the Effectiveness of Emergency Lighting, Retroreflective Markings, and Paint Color on Policing and Law Enforcement Safety
    Terry, Travis N. (Virginia Tech, 2020-07-01)
    This project is an in-depth investigation on the impact of lighting, marking and paint schemes on the operational aspects of police vehicles. This investigation consisted of two phases that ultimately consisted of four experiments. An array of lighting and marking schemes were implemented on police vehicles in a variety of jurisdictions for evaluation. The study then investigated the change in the visibility of police officers, the public reaction to these schemes, and the operational impacts of these systems. The first phase of the project was a naturalistic observation study where the goal was to better understand how traffic behaved around traffic stops. Test vehicles were positioned in simulated traffic stops and patrol locations to determine how traffic behavior was affected by various configurations of police lighting and markings. Camera and radar systems were used to measure the changes in driver speed and when drivers responded to the move over law. Based on the results of the naturalistic studies, the impact of the lighting system on officer visibility was investigated in a controlled human factors test where the ability of a driver to see a police officer outside of their vehicle was measured in the presence of the lighting systems. The purpose of this interjected effort was to verify that the experimental schemes would not increase risk to law enforcement despite data from the first phase indicating the vehicles were more visible. A second part to that study evaluated conventional methods of bolstering an officer's visibility outside of their vehicle at night. The second phase took the findings of the first phase and implemented changes to several police vehicles from local and state agencies to be in operation for at least 18 months. This was to assess the rate of near-misses and crash rate to relate the vehicle changes to law enforcement safety. Additionally, rates of citations were assessed, and surveys offered an opportunity for law enforcement to provide their own feedback on the implementations. The lighting systems evaluated included a completely blue lighting system, an enhanced all blue lighting system with twice the light output, a red and blue system, and a single flashing blue beacon. In terms of markings, retroreflective markings along the side of the vehicle, a retroreflective contour line, chevrons on the rear of the vehicle and unmarked vehicles were evaluated. Finally, a variety of vehicle colors were used to investigate the impact of the base vehicle paint color. The results indicate that both the red and blue lighting system and the high output blue lighting system increase the distance at which drivers moved over significantly. In general, at least 95% of traffic attempted to merge away from an actively lighted police vehicle, when possible. In terms of the speed change, drivers began reducing their speed by approximately 600 m from the police vehicle. Similarly, the addition of retroreflectivity to the rear of the vehicle showed an additional benefit for causing drivers to move over sooner. However, these benefits came at a cost to the officer's visibility. When outside of their vehicle, the high output blue system significantly reduced officer detectability while the red and blue configuration only impacted detection distance by 3 meters. The investigation did find that these impacts could be overcome with retroreflective vests worn by the officers. In the second phase, a preference revealed by officers favored the red-blue configuration. They stated that this configuration provided greater comfort for them and less glare to approaching drivers. The study also revealed that the alternative configurations did not impact the operational activities of police authority.
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    Behavioral Adaptation to Driving Automation Systems: Guidance for Consumer Education
    Noble, Alexandria Marie (Virginia Tech, 2020-04-15)
    Researchers have postulated that the implementation of driving automation systems could reduce the prevalence of driver errors, or at least mitigate the severity of their consequences. While driving automation systems are becoming increasingly common on new vehicles, drivers seem to know very little about them. The following dissertation describes an investigation of driver behavior and behavioral adaptation while using driving automation systems in order to improve consumer education and training. This dissertation uses data collected from test track environments and two naturalistic driving studies, the Virginia Connected Corridor 50 (VCC50) Vehicle Naturalistic Driving Study and the NHTSA Level 2 Naturalistic Driving Study (L2 NDS), to investigate driver behavior with driving automation systems and make suggestions for modifications to current consumer education practices. Results from the test track study indicated that while training strategy elicited limited differences in knowledge and no difference in driver behaviors or attitudes, operator behaviors and attitudes were heavily influenced by time and experience with the driving automation. The naturalistic assessment of VCC50 data showed that drivers tended to activate systems more frequently in appropriate roadway environments. However, drivers spent more time looking away from the road while driving automation systems were active and drivers were more likely be observed browsing on their cell phones while using driving automation systems. The analysis of L2 NDS showed that drivers' time gap preferences changes as drivers gain experience using the driving automation systems. Additionally, driver eye glance behavior was significantly different with automation use and indicated the potential for an adaptive trend with increased exposure to the system for both glances away from the roadway and glances to the instrument panel. The penultimate chapter of this work presents training guidelines and recommendations for consumer education with driving automation systems based on this and other research that has been conducted on driver interaction with driving automation systems. The results of this research indicate that driver training should be a key focus in future efforts to ensure the continued safe use of driving automation systems as they continue to emerge in the vehicle fleet.  
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    Behavioral Monitoring to Identify Self-Injurious Behavior among Children with Autism Spectrum Disorder
    Garside, Kristine Dianne Cantin (Virginia Tech, 2019-03-25)
    Self-injurious behavior (SIB) is one of the most dangerous behavioral responses among individuals with autism spectrum disorder (ASD), often leading to injury and hospitalization. There is an ongoing need to measure the triggers of SIB to inform management and prevention. These triggers are determined traditionally through clinical observations of the child with SIB, often involving a functional assessment (FA), which is methodologically documenting responses to stimuli (e.g., environmental or social) and recording episodes of SIB. While FA has been a "gold standard" for many years, it is costly, tedious, and often artificial (e.g., in controlled environments). If performed in a naturalistic environment, such as the school or home, caregivers are responsible for tracking behaviors. FA in naturalistic environments relies on caregiver and patient compliance, such as responding to prompts or recalling past events. Recent technological developments paired with classification methods may help decrease the required tracking efforts and support management plans. However, the needs of caregivers and individuals with ASD and SIB should be considered before integrating technology into daily routines, particularly to encourage technology acceptance and adoption. To address this, the perspectives of SIB management and technology were first collected to support future technology design considerations (Chapter 2). Accelerometers were then selected as a specific technology, based on caregiver preferences and reported preferences of individuals with ASD, and were used to collect movement data for classification (Chapter 3). Machine learning algorithms with featureless data were explored, resulting in individual-level models that demonstrated high accuracy (up to 99%) in detecting and classifying SIB. Group-level classifiers could provide more generalizable models for efficient SIB monitoring, though the highly variable nature of both ASD and SIB can preclude accurate detection. A multi-level regression model (MLR) was implemented to consider such individual variability (Chapter 4). Both linear and nonlinear measures of motor variability were assessed as potential predictors in the model. Diverse classification methods were used (as in Chapter 3), and MLR outperformed other group level classifiers (accuracy ~75%). Findings from this research provide groundwork for a future smart SIB monitoring system. There are clear implications for such monitoring methods in prevention and treatment, though additional research is required to expand the developed models. Such models can contribute to the goal of alerting caregivers and children before SIB occurs, and teaching children to perform another behavior when alerted.
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    Biomechanical Analysis and Modeling of Back-Support Exoskeletons for Use in Repetitive Lifting Tasks
    Madinei, Seyed Saman (Virginia Tech, 2022-01-07)
    Low back pain (LBP) remains the most prevalent and costly work-related disability worldwide and is directly associated with "physical" risk factors prevalent in manual material handling (MMH) tasks. Back-support exoskeletons (BSEs) are a promising ergonomic intervention to mitigate LBP risk, by reducing muscular exertion and spine loading. The purpose of this work was to help better understand both the "intended" and "unintended" consequences of BSE use on physical risk factors for LBP, as an essential prerequisite for the safe and effective implementation of this technology in actual workplaces. The first study assessed the effects of using two BSEs on objective and subjective responses during repetitive lifting involving symmetric and asymmetric postures. Wearing both BSEs significantly reduced peak levels of trunk extensor muscle activity and reduced energy expenditure. Such reductions, though, were more pronounced in the symmetric conditions and differed between the two BSEs tested. The second study quantified the assistive torque profiles of two passive BSEs using a computerized dynamometer, with both human subjects and a mannequin. Clear differences in torque magnitudes were evident between the BSEs, though both generated more assistive torques during flexion than extension. The third study estimated the effects of BSE use on lumbosacral compressive and shear forces during repetitive lifting using an optimization-based model. Using both BSEs reduced peak compression and anteroposterior shear forces, but these effects differed between tasks and BSE designs. Reductions in composite measures of trunk muscle activity did not correspond consistently with changes in spine forces when using a BSE. The fourth study quantified the effects of two passive BSEs on trunk stability and movement coordination during repetitive lifting. Some adverse effects on stability were evident for pelvis and thorax movements and coupling of these body segments, suggesting that caution is needed in selecting a BSE for a given MMH task. Overall, we found that the efficacy of BSEs is design- and task-specific. Important safety features of the exoskeletons were also identified, providing insights on their performance boundaries. Overall, the BSEs tested were more effective and safer in tasks closer to the mid-sagittal plane and with moderate degrees of trunk flexion.
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    Changes in kinematics and muscle activity when learning to use a whole-body powered exoskeleton for stationary load handling
    Park, Hanjun; Kim, Sunwook; Nussbaum, Maury A.; Srinivasan, Divya (SAGE, 2022-10-11)
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    Changes in lower-limb joint torques when using a passive back-support exoskeleton for level walking
    Park, Jang-Ho; Kim, Sunwook; Nussbaum, Maury A.; Srinivasan, Divya (SAGE, 2021-09)
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    Characterizing Mental Workload in Physical Human-Robot Interaction Using Eye-Tracking Measures
    Upasani, Satyajit Abhay (Virginia Tech, 2023-07-06)
    Recent technological developments have ushered in an exciting era for collaborative robots (cobots), which can operate in close proximity with humans, sharing and supporting task goals. While there is increasing research on the biomechanical and ergonomic consequences of using cobots, there is relatively little work on the potential motor-cognitive demand associated with these devices. These cognitive demands primarily stem from the need to form accurate internal (mental) models of robot behavior, while also dealing with the intrinsic motor-cognitive demands of physical co-manipulation tasks, and visually monitoring the environment to ensure safe operation. The primary aim of this work was to investigate the viability of eye-tracking measures for characterizing mental workload during the use of cobots, while accounting for the potential effects of learning, task-type, expertise, and age-differences. While eye-tracking is gaining traction in surgical/rehabilitation robotics domains, systematic investigations of eye tracking for studying interactions with industrial cobots are currently lacking. We conducted three studies in which participants of different ages and expertise levels learned to perform upper- and lower-limb tasks using a dual-armed cobot and a whole-body powered exoskeleton respectively, over multiple trials. Robot-control difficulty was manipulated by changing the joint impedance on one of the robot arms (for the dual-armed cobot). The first study demonstrated that when individuals were learning to interact with a dual-armed cobot to perform an upper-limb co-manipulation task simulated in a virtual reality (VR) environment, pupil dilation (PD) and stationary gaze entropy (SGE) were the most sensitive and reliable measures of mental workload. A combination of eye-tracking measures predicted performance with greater accuracy than experimental task variables. Measures of visual attentional focus were more sensitive to task difficulty manipulations than typical eye-tracking workload measures, and PD was most sensitive to changes in workload over learning. The second study showed that compared to walking freely, walking while using a complex whole-body powered exoskeleton: a) increased PD of novices but not experts, b) led to reduced SGE in both groups and c) led to greater downward focused gaze (on the walking path) in experts compared to novices. In the third study using an upper-limb co-manipulation task similar to Study 1, we found that the PD of younger adults reduced at a faster rate over learning, compared to that of older adults, and older adults showed a significantly greater drop in gaze transition entropy with an increase in task difficulty, compared to younger adults. Also, PD was sensitive to learning and robot-difficulty but not environmental-complexity (collisions with objects in the task environment), and gaze-behavior measures were generally more sensitive to environmental-complexity. This research is the first to conduct a comprehensive analysis of mental workload in physical human-robot interaction using eye-tracking measures. PD was consistently found to show larger effects over learning, compared to task difficulty. Gaze-behavior measures quantifying visual attention towards environmental areas of interest were found to show relatively large effects of task difficulty and should continue to be explored in future research. While walking in a powered exoskeleton, both novices and experts exhibited compensatory gaze strategies. This finding highlights potentially persistent effects of using cobots on visual attention, with potential implications to safety and situational awareness. Older adults were found to apply greater mental effort (indicated by sustained PD) and followed more constrained gaze patterns in order to maintain similar levels of performance to younger adults. Perceived workload measures could not capture these age-differences, thus highlighting the advantages of eye-tracking measures. Lastly, the differential sensitivity of pupillary- and gaze behavior metrics to different types of task demands highlights the need for future research to employ both kinds of measures for evaluating pHRI. Important questions for future research are the potential sensitivity of eye-tracking workload measures over long-term adaptations to cobots, and the potential generalizability of eye-tracking measures to real-world (non-VR) tasks.
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    Comparison of Augmented Reality Rearview and Radar Head-Up Displays for Increasing Spatial Awareness During Exoskeleton Operation
    Hollister, Mark Andrew (Virginia Tech, 2024-03-19)
    Full-body powered exoskeletons for industrial workers have the potential to reduce the incidence of work-related musculoskeletal disorders while increasing strength beyond human capabilities. However, operating current full-body powered exoskeletons imposes different loading, motion, and balance requirements on users compared to unaided task performance, potentially resulting in additional mental workload on the user which may reduce situation awareness (SA) and increase risk of collision with pedestrians, negating the health and safety benefits of exoskeletons. Exoskeletons could be equipped with visual aids to improve SA, like rearview cameras or radar displays. However, research on design and evaluation of such displays for exoskeleton users are absent in the literature. This empirical study compared several augmented reality (AR) head-up displays (HUDs) in providing SA to minimize pedestrian collisions while completing common warehouse tasks. Specifically, the study consisted of an experimental factor of display abstraction including four levels, from low to high abstraction: rearview camera, overhead radar, ring radar, and no visual aid (as control). The second factor was elevation angle that was analyzed with the overhead and ring radar displays at 15°, 45°, and 90°. A 1x4 repeated measures ANOVA on all four display abstraction levels at 90° revealed that every display condition performed better than the no visual aid condition, the Bonferroni post-hoc test revealed that overhead and ring radars (medium and high abstraction respectively) received higher usability ratings than the rearview camera (low abstraction). A 2x3 repeated measures ANOVA on the two radar displays at all three display angles found that the overhead radar yielded better transport time and situation awareness ratings than the ring radar. Further, the two-way ANOVA found that 45° angles yielded the best transport collision times. Thus, AR displays presents promise in augment SA to minimize collision risk to collision and injury in warehouse settings.
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    A Connected Work Zone Hazard Detection System for Highway Construction Work Zones
    Han, Wenjun (Virginia Tech, 2019-07-02)
    Roadway construction workers have to work in close proximity to construction equipment as well as high-speed traffic, exposing them to an elevated risk of collisions. This research aims to develop an innovative holistic solution to reduce the risk of collisions at roadway work zones. To this end, a connected hazard detection and prevention system is developed to detect potential unsafe proximities in highway work zones and provide warning and instructions of imminent threats. This connected system collects real-time information from all the actors inside and outside of the work zone and communicates it with a cloud server. A hazard detection algorithm is developed to identify potential proximity hazards between workers and connected/automated vehicles (CAV) and/or construction equipment. Detected imminent threats are communicated to in-danger workers and/or drivers. The trajectories and safety status of each actor is visualized on Virginia Connected Corridors (VCC) Monitor, a custom web-based situational awareness tool, in real-time. To assure the accuracy of hazard detection, the algorithm accommodates various parameters including variant threat zones for workers-on-foot, vehicles, and equipment, the direction of movement, workers' distance to the work zone border, shape of road, etc. The designed system is developed and evaluated through various experiments on the Virginia's Smart Roads located at Virginia Tech. Data regarding activities of workers-on-foot was collected during experiments and was used and classified for activity recognition using supervised machine learning methods. A demonstration was held to evaluate the usability of the developed system, and the results proved the efficacy of the algorithm in successfully detecting potential collisions and provide prompt warnings and instructions. The developed holistic system elevates safety of highway construction and maintenance workers at work sites. It also helps managers and inspectors to keep track of the real-time safety status of their work zone actors as well as the accidents occurrences. As such, with the connected work zone hazard detection system, the safety level and productivity of the workers is expected to be greatly enhanced.
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    Consistency of Sedentary Behavior Patterns among Office Workers with Long-Term Access to Sit-Stand Workstations
    Huysmans, Maaike A.; Srinivasan, Divya; Mathiassen, Svend Erik (Oxford University Press, 2019-04-22)
    Introduction: Sit-stand workstations are a popular intervention to reduce sedentary behavior (SB) in office settings. However, the extent and distribution of SB in office workers long-term accustomed to using sit-stand workstations as a natural part of their work environment are largely unknown. In the present study, we aimed to describe patterns of SB in office workers with long-term access to sit-stand workstations and to determine the extent to which these patterns vary between days and workers. Methods: SB was objectively monitored using thigh-worn accelerometers for a full week in 24 office workers who had been equipped with a sit-stand workstation for at least 10 months. A comprehensive set of variables describing SB was calculated for each workday and worker, and distributions of these variables between days and workers were examined. Results: On average, workers spent 68% work time sitting [standard deviation (SD) between workers and between days (within worker): 10.4 and 18.2%]; workers changed from sitting to standing/ walking 3.2 times per hour (SDs 0.6 and 1.2 h−1); with bouts of sitting being 14.9 min long (SDs 4.2 and 8.5 min). About one-third of the workers spent >75% of their workday sitting. Between-workers variability was significantly different from zero only for percent work time sitting, while betweendays (within-worker) variability was substantial for all SB variables. Conclusions: Office workers accustomed to using sit-stand workstations showed homogeneous patterns of SB when averaged across several days, except for percent work time seated. However, SB differed substantially between days for any individual worker. The finding that many workers were extensively sedentary suggests that just access to sit-stand workstations may not be a sufficient remedy against SB; additional personalized interventions reinforcing use may be needed. To this end, differences in SB between days should be acknowledged as a potentially valuable source of variation.
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    Consistent individual motor variability traits demonstrated by females performing a long-cycle assembly task under conditions differing in temporal organisation
    Jackson, Jennie A.; Srinivasan, Divya; Mathiassen, Svend Erik (2020-05)
    Research suggests an association between motor variability (MV) during repetitive work and work-related musculoskeletal disorders (MSDs). However, whether MV is a consistent individual trait, even across working conditions or tasks, remains unknown. This study assessed whether individual MV traits were consistent during complex work performed under different temporal conditions. Fifteen women performed cyclic assembly under four conditions differing in pace and organisation (line-type, batch-type). MV of trapezius muscle activity and upper arm elevation was quantified and partitioned into variance components. For all MV metrics, a non-zero between-subjects variance was found, indicating consistent individual MV traits across conditions. Variance between subjects was higher for electromyography (EMG) MV metrics compared with kinematic metrics. Our results showed individuals exhibited consistent MV traits across working conditions differing in pace and production process. Further research is needed to understand whether MV is an individual predictive factor for MSD onset or progression.
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    A data-driven approach to understand factors contributing to exoskeleton use-intention in construction
    Kim, Sunwook; Moore, Albert; Ojelade, Aanuoluwapo; Gutierrez, Nancy; Harris-Adamson, Carisa; Barr, Alan; Srinivasan, Divya; Nussbaum, Maury A. (SAGE, 2023-10-25)
    Work-related musculoskeletal disorders (WMSDs) remain an important heath concern for construction workers. Occupational exoskeletons (EXOs) are a new ergonomic intervention to control WMSD risk, yet their adoption has been low in construction. We explored contributing factors to EXO use-intention, by building a decision tree to predict the intention to try an exoskeleton using responses to an online survey. Variable selection and hyperparameter tuning were used respectively to reduce the number of potential predictors, and for a better prediction performance. Performance was assessed using four common metrics. The importance of variables in the final tree was calculated to understand which variable had a greater influence. The final tree had moderate prediction performance. Important variables identified were associated with opinions on EXO use, demographics, job demands, and perceived potential risks. The key influential variables were EXOs becoming standard equipment and fatigue reduction with EXO use. Practical implications of the findings are discussed.
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    Design and Prototype of an Active Knee Exoskeleton to Aid Farmers with Mobility Limitations
    Wood, Evan A. (Virginia Tech, 2019-09-10)
    As farmers continue to get older, they will likely face age-related disabilities that impede their ability to work and increase risk of suffering serious injuries. One of the major age- related diseases is arthritis, which currently accounts for about 40% of disability cases in agriculture nationwide. The effect of arthritis on farmers is profound because it reduces their physical strength, joint range of motion and is a source of joint pain, all culminating in the lack of ability to perform routine activities regularly and safely. One way to decrease the rate of injuries is by reducing the strength and joint loading required to perform these activities through the use of wearable robotics. As opposed to existing solutions that focus only on injury prevention, this thesis will present an active, knee-assist exoskeleton intent on providing 30% of the necessary joint rotation force to perform activities such as sit-to- stand actions and the ascent/descent of stairs and hills. The device will be a lightweight, unobtrusive cable-driven exoskeleton actuated by distally-worn electric motors. We hope that use of the exoskeleton will result in increased ranges of motion and overall reduction of stress on the wearer's body, which will minimize the effects of arthritis and ultimately improve safety and quality of life.
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    Development and Assessment of Smart Textile Systems for Human Activity Classification
    Mokhlespour Esfahani, Mohammad Iman (Virginia Tech, 2018-09-13)
    Wearable sensors and systems have become increasingly popular for diverse applications. An emerging technology for physical activity assessment is Smart Textile Systems (STSs), comprised of sensitive/actuating fiber, yarn, or fabric that can sense an external stimulus. All required components of an STS (sensors, electronics, energy supply, etc.) can be conveniently embedded into a garment, providing a fully textile-based system. Thus, STSs have clear potential utility for measuring health-relevant aspects of human activity, and to do so passively and continuously in diverse environments. For these reasons, STSs have received increasing interest in recent studies. Despite this, however, limited evidence exists to support the implementation of STSs during diverse applications. Our long-term goal was to assess the feasibility and accuracy of using an STS to monitor human activities. Our immediate objective was to investigate the accuracy of an STS in three representative applications with respect to occupational scenarios, healthcare, and activities of daily living. A particular STS was examined, consisting of a smart socks (SSs), using textile pressure sensors, and smart undershirt (SUS), using textile strain sensors. We also explored the relative merits of these two approaches, separately and in combination. Thus, five studies were completed to design and evaluate the usability of the smart undershirt, and investigate the accuracy of implementing an STS in the noted applications. Input from the SUS led to planar angle estimations with errors on the order of 1.3 and 9.4 degrees for the low-back and shoulder, respectively. Overall, individuals preferred wearing a smart textile system over an IMU system and indicated the former as superior in several aspects of usability. In particular, the short-sleeved T-shirt was the most preferred garments for an STS. Results also indicated that the smart shirt and smart socks, both individually and in combination, could detect occupational tasks, abnormal and normal gaits, and activities of daily living with greater than 97% accuracy. Based on our findings, we hope to facilitate future work that more effectively quantifies sedentary periods that may be deleterious to human health, as well as detect activity types that may be help or hinder health and fitness. Such information may be of use to individuals and workers, healthcare providers, and ergonomists. More specifically, further analyses from this investigation could provide strategies for: (a) modifying a sedentary lifestyle or work scenario to a more active one, and (b) helping to more accurately identify occupational injury risk factors associated with human movement.
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    Development of supine and standing knee joint position sense tests
    Strong, Andrew; Srinivasan, Divya; Häger, Charlotte K. (2021-05)
    Objectives: We aimed to assess the test-retest reliability of a supine and standing knee joint position sense (JPS) test, respectively, and whether they discriminate knees with anterior cruciate ligament (ACL) injury from asymptomatic knees. Design: Repeated measures and cross-sectional. Setting: Research laboratory. Participants: For test-retest reliability, 24 persons with asymptomatic knees. For discriminative analysis: 1) ACLR -18 persons on average 23 months after unilateral ACL reconstruction, 2) CTRL - 23 less-active persons, and 3) ATHL - 21 activity level-matched athletes. Main outcome measures: Absolute error (AE) and variable error (VE). Results: Test-retest reliability was generally highest for AE of the standing test (ICC 0.64-0.91). Errors were less for the standing compared to the supine test across groups. CTRL had greater knee JPS AE (P = 0.005) and VE (P = 0.040) than ACLR. ACLR knees showed greater VE compared to the contralateral non-injured knees for both tests (P = 0.032), albeit with a small effect size (eta(2)(p) = 0.244). Conclusions: Our standing test was more reliable and elicited lesser errors than our supine test. Less-active controls, rather than ACLR, produced significantly greater errors. Activity level may be a more predominant factor than ACLR for knee JPS similar to 2 years post-reconstruction. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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    Effects of back-support exoskeleton use on gait performance and stability during level walking
    Park, Jang-Ho; Kim, Sunwook; Nussbaum, Maury A.; Srinivasan, Divya (Elsevier, 2022-02-01)
    Background: Back-support exoskeletons (BSEs) are a promising intervention to mitigate physical demands at work. Although growing evidence indicates that BSEs can reduce low-back physical demands, there is limited understanding of potential unintended consequences of BSE use, including the risk of falls. Research question: Does using a BSE adversely affect gait performance and stability, and are such effects dependent on specific BSE external torque characteristics? Methods: Twenty participants (10 M, 10 F) completed five level over-ground walking trials and a five-minute treadmill walking trial while wearing a BSE (backX™) with three different levels of external torque (i.e., no torque, low torque, and high torque) and in a control (no-exoskeleton) condition. Spatiotemporal gait patterns, stride-to-stride gait variability measures, required coefficient-of-friction (RCoF), and minimum foot clearance (MFC) were determined, to assess gait performance. Gait stability was quantified using the maximum Lyapunov exponent (MLE) of trunk kinematics and the margin-of-stability (MoS). Results: Using the backX™ with high supportive torque decreased slip risk (7% decrease in RCoF) and slightly improved trunk stability (3% decrease in MLE). However, it also decreased step length (1%), increased step width (10%) and increased gait variability (8–19%). Changes in MoS were complex: while MoS at heel strike decreased in the AP direction, it increased in the ML direction. There was a rather large decrease in MoS (26%) in the ML direction during the swing phase. Significance: This is the first study to quantify the effects of wearing a passive BSE with multiple supportive torque levels on gait performance and stability during level walking. Our results, showing that the external torque of the BSE may adversely affect gait step width, variability, and dynamic stability, can contribute to better design and practice guidelines to facilitate the safe adoption of BSEs in the workplace.
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    Effects of back-support exoskeleton use on lower limb joint kinematics and kinetics during level walking
    Park, Jang-Ho; Lee, Youngjae; Madinei, Saman; Kim, Sun Wook; Nussbaum, Maury A.; Srinivasan, Divya (Springer, 2022-04-27)
    We assessed the effects of using a passive back-support exoskeleton (BSE) on lower limb joint kinematics and kinetics during level walking. Twenty young, healthy participants completed level walking trials while wearing a BSE (backXTM) with three different levels of hip-extension support torque (i.e., no torque, low, and high) and in a control condition (no-BSE). When hip extension torques were required for gait-initial 0-10% and final 75-100% of the gait cycle-the BSE with high supportive torque provided ~ 10 Nm of external hip extension torque at each hip, resulting in beneficial changes in participants' gait patterns. Specifically, there was a ~ 10% reduction in muscle-generated hip extension torque and ~ 15-20% reduction in extensor power. During the stance-swing transition, however, BSE use produced undesirable changes in lower limb kinematics (e.g., 5-20% increase in ankle joint velocity) and kinetics (e.g., ~ 10% increase in hip flexor, knee extensor, and ankle plantarflexor powers). These latter changes likely stemmed from the need to increase mechanical energy for propelling the leg into the swing phase. BSE use may thus increase the metabolic cost of walking. Whether such use also leads to muscle fatigue and/or postural instability in long-distance walking needs to be confirmed in future work.