Wearing a back-support exoskeleton alters lower-limb joint kinetics during single-step recovery following a forward loss of balance.

We assessed the effects of a passive, back-support exoskeleton (BSE) on lower-limb joint kinetics during the initiation and swing phases of recovery from a forward loss of balance. Sixteen (8M, 8F) young, healthy participants were released from static forward-leaning postures and attempted to recover their balance with a single-step while wearing a BSE (backXTM) with different levels of support torque and in a control condition. The BSE provided âˆ¼ 15-20 Nm of external hip extension torque on the stepping leg at the end of initiation and beginning of swing phases. Participants were unable to generate sufficient hip flexion torque, power, and work to counteract this external torque, although they sustained hip flexion torque for a more prolonged period, resulting in slightly increased hip contribution to positive leg work (compared to control). However, net positive leg work, and the net contribution of hip joint (human + BSE) to total leg work decreased with BSE use. While all participants had changes in hip joint kinetics, a significant compensatory increase in ankle contribution to positive leg work was observed only among females. Our results suggest that BSE use adversely affects reactive stepping by decreasing the stepping leg kinetic energy for forward propulsion, and that the relative contributions of lower-limb joints to total mechanical work done during balance recovery are altered by BSE use. BSEs may thus need to be implemented with caution for dynamic tasks in occupational settings, as they may impair balance recovery following a forward loss of balance.

Age and gender differences in the perception and use of soft vs. rigid exoskeletons for manual material handling.

We investigated age and gender differences in the perception and use of soft (Apex) vs. rigid (Paexo Back) passive back-support exoskeletons (BSE) for repetitive lifting and lowering. A gender-balanced sample of 20 young (18-30 years) and 16 old (45-60 years) individuals were recruited. In the first session, participants' self-reported maximum acceptable load (MAL) was assessed using a psychophysical approach. Changes in muscle activity and kinematics due to BSE use in repetitive lifting/lowering tasks were also assessed. Overall, both BSEs increased MAL (by ∼7%), and reduced trunk extensor muscle activity across all groups (by ∼7-18%), compared to the control condition. Both BSEs promoted more squatting postures, increased quadriceps muscle activity (by ∼34%) and abdominal muscle activity during asymmetric tasks (by 5-20%). Some age and gender differences were significant, particularly for the trunk kinematics when using the Apex. Future work should include more diverse user groups in studying willingness to adopt BSEs and characterising their consequent effects on the body.

Manual material handling is difficult to eliminate in several industries. There are now viable rigid and soft exosuit systems that can offer varying levels of support. We found both kinds of exoskeletons to be equally effective in reducing trunk extensor muscle activity, among young and old males and females.

Effects of arm-support exoskeletons on pointing accuracy and movement.

Exoskeletons are wearable devices that support or augment users' physical abilities. Previous studies indicate that they reduce the physical demands of repetitive tasks such as those involving heavy material handling, work performed with arms elevated, and the use of heavy tools. However, there have been concerns about exoskeletons hindering movement and reducing its precision. To this end, the current study investigated how proprioception enables people to point to targets in a blindfolded, repetitive pointing task, and their ability to recalibrate their pointing movement based on visual feedback during an intervening calibration phase, both with and without an arm-support exoskeleton. On each trial, participants were instructed to follow a 40 BPM metronome to point six times alternating between two target points placed either on a vertical or horizontal line. Within a trial, each pointing movement alternated between flexion and extension. Results indicate that participants' average pointing error increased by 4% when they wore an exoskeleton, compared to when they did not. The average pointing error was 12% lower when the target points were aligned vertically as compared to horizontally. It was also observed that the average pointing error was 14% lower during flexion as compared to extension movement. Surprisingly, accuracy did not improve in the post-test as compared to the pre-test phase, likely due to accuracy being high from the beginning. Participants' movement dynamics were analyzed using Recurrence Quantification Analysis. It was found that movements were less deterministic (1% reduction in percentage of determinism) and less stable (13.6% reduction in average diagonal line length on the recurrence plot) when they wore the exoskeleton as compared to when they did not. These results have implications on the design of arm-support exoskeletons and for facilitating their integration into the natural motor synergies in humans.

The compatibility of exoskeletons in perioperative environments and workflows: an analysis of surgical team members' perspectives and workflow simulation.

Surgical team members in perioperative environments experience high physical demands. Interventions such as exoskeletons, external wearable devices that support users, have the potential to reduce these work-related physical demands. However, barriers such as workplace environment and task compatibility may limit exoskeleton implementation. This study gathered the perspectives of 33 surgical team members: 12 surgeons, four surgical residents, seven operating room (OR) nurses, seven surgical technicians (STs), two central processing technicians (CPTs), and one infection control nurse to understand their workplace compatibility. Team members were introduced to passive exoskeletons via demonstrations, after which surgical staff (OR nurses, STs, and CPTs) were led through a simulated workflow walkthrough where they completed tasks representative of their workday. Five themes emerged from the interviews (workflow, user needs, hindrances, motivation for intervention, and acceptance) with unique subthemes for each population. Overall, exoskeletons were largely compatible with the duties and workflow of surgical team members.

The goal of this study was to identify exoskeleton compatibility across various surgical team members through a thematic analysis of interviews and a simulated workflow walkthrough. Results revealed five unique themes (workflow, user needs, hinderances, motivation for intervention, acceptance) and that exoskeletons were largely compatible with daily duties.

Understanding contributing factors to exoskeleton use-intention in construction: a decision tree approach using results from an online survey.

Work-related musculoskeletal disorders (WMSDs) are a major health concern in the construction industry. Occupational exoskeletons (EXOs) are a promising ergonomic intervention to help reduce WMSD risk. Their adoption, however, has been low in construction. To understand the contributing factors to EXO use-intention and assist in future decision-making, we built decision trees to predict responses to each of three EXO use-intention questions (Try, Voluntary Use, and Behavioural Intention), using online survey responses. Variable selection and hyperparameter tuning were used respectively to reduce the number of potential predictors and improve prediction performance. The importance of variables in each final tree was calculated to understand which variables had a greater influence. The final trees had moderate prediction performance. The root node of each tree included EXOs becoming standard equipment, fatigue reduction, or performance increase. Important variables were found to be quite specific to different decision trees. Practical implications of the findings are discussed.Practitioner summary: This study used decision trees to identify key factors influencing the use-intention of occupational exoskeletons (EXOs) in construction, using online survey data. Key factors identified included EXOs becoming standard equipment, fatigue reduction, and performance improvement. Final trees provide intuitive visual representations of the decision-making process for workers to use EXOs.

Do Sit-Stand Tables Affect Physical Behavior and Body Composition Similarly in Normal-Weight and Overweight Office Workers? A Pilot Study.

OCCUPATIONAL APPLICATIONSSedentary behavior is a significant health concern among office workers. We completed the same 6-month sit-stand table intervention at work for groups of normal-weight and overweight workers, and compared it to not having sit-stand tables. The intervention caused the intended decrease in sitting time in both groups and a corresponding increase in standing. We did not find compensation effects on physical behavior outside of work. Furthermore, the intervention did not change the composition of fat, lean, and bone mass in either group. Thus, strategies including initiatives to increase physical activity are likely needed to have effects on body composition; and an intervention needs to be sustained for longer than six months for any changes in body composition to be observed.

Background: A sit-stand table (SST) at work may help office workers shorten and break up sitting by periods of standing. However, it is not clear whether SST use influences sitting at and outside work to similar extents among normal-weight and overweight office workers, and whether it can change body composition. Purpose: To investigate if introducing SSTs affects physical behavior and body composition similarly in normal-weight and overweight office workers. Methods: In this pilot intervention study, physical behavior and body composition were evaluated and compared between normal-weight (n = 8) and overweight (n = 14) office workers, both before and after using an SST for 6 months. Time spent sitting, standing, and moving was recorded using a triaxial thigh accelerometer during work and leisure. Dual-energy X-ray absorptiometry was used to determine fat, lean, and bone mass. Physical behavior and body composition data were both processed using compositional data analysis. Results: The intervention was similarly effective for normal weight and overweight workers in changing physical behavior during work, mainly by reducing sitting time and increasing standing time, while no effects were seen during leisure. We found no effect of the intervention on body composition. Conclusion: A sit-stand table intervention for 6 months changed physical behaviors at work to a similar extent among normal weight and overweight office workers. No compensatory behaviors were observed during leisure, and the intervention had no significant effects on body composition.

Sensemaking, adaptation and agency in human-exoskeleton synchrony.

Introduction: Wearable I robots such as exoskeletons combine the strength and precision of intelligent machines with the adaptability and creativity of human beings. Exoskeletons are unique in that humans interact with the technologies on both a physical and cognitive level, and as such, involve a complex, interdependent relationship between humans and robots. The aim of this paper was to explore the concepts of agency and adaptation as they relate to human-machine synchrony, as human users learned to operate a complex whole-body powered exoskeleton. Methods: Qualitative interviews were conducted with participants over multiple sessions in which they performed a range of basic functional tasks and simulated industrial tasks using a powered exoskeleton prototype, to understand their expectations of the human-technology partnership, any challenges that arose in their interaction with the device, and what strategies they used to resolve such challenges. Results: Analysis of the data revealed two overarching themes: 1) Participants faced physical, cognitive, and affective challenges to synchronizing with the exoskeleton; and 2) they engaged in sensemaking strategies such as drawing analogies with known prior experiences and anthropomorphized the exoskeleton as a partner entity in order to adapt and address challenges. Discussion: This research is an important first step to understanding how humans make sense of and adapt to a powerful and complex wearable robot with which they must synchronize in order to perform tasks. Implications for our understanding of human and machine agency as well as bidirectional coadaptation principles are discussed.

Eye-Tracking in Physical Human-Robot Interaction: Mental Workload and Performance Prediction.

BACKGROUND: In Physical Human-Robot Interaction (pHRI), the need to learn the robot's motor-control dynamics is associated with increased cognitive load. Eye-tracking metrics can help understand the dynamics of fluctuating mental workload over the course of learning. OBJECTIVE: The aim of this study was to test eye-tracking measures' sensitivity and reliability to variations in task difficulty, as well as their performance-prediction capability, in physical human-robot collaboration tasks involving an industrial robot for object comanipulation. METHODS: Participants (9M, 9F) learned to coperform a virtual pick-and-place task with a bimanual robot over multiple trials. Joint stiffness of the robot was manipulated to increase motor-coordination demands. The psychometric properties of eye-tracking measures and their ability to predict performance was investigated. RESULTS: Stationary Gaze Entropy and pupil diameter were the most reliable and sensitive measures of workload associated with changes in task difficulty and learning. Increased task difficulty was more likely to result in a robot-monitoring strategy. Eye-tracking measures were able to predict the occurrence of success or failure in each trial with 70% sensitivity and 71% accuracy. CONCLUSION: The sensitivity and reliability of eye-tracking measures was acceptable, although values were lower than those observed in cognitive domains. Measures of gaze behaviors indicative of visual monitoring strategies were most sensitive to task difficulty manipulations, and should be explored further for the pHRI domain where motor-control and internal-model formation will likely be strong contributors to workload. APPLICATION: Future collaborative robots can adapt to human cognitive state and skill-level measured using eye-tracking measures of workload and visual attention.

Manufacturing Industry Stakeholder Perspectives on Occupational Exoskeletons: Changes after a Brief Exposure to Exoskeletons.

OCCUPATIONAL APPLICATIONSMultiple occupational exoskeletons have been developed recently with potential to reduce physical demands, muscle fatigue, and risk of over-exertion injuries in manufacturing, yet there are currently challenges in practical, large-scale deployment. We explored how stakeholder perceptions of exoskeletons were affected by exposure to passive arm- and back-support exoskeletons. Our outcomes indicate that even brief exposure to exoskeletons can positively influence worker and stakeholder perceptions on the usefulness and safety of exoskeletons. However, worker concerns about device usability and acceptability in the field were not mitigated by such brief exposure. This work may help manufacturing industry stakeholders understand what technology-adoption factors need further consideration when planning for exoskeleton deployment.

Background: Despite evidence from several laboratory studies on the effectiveness of passive exoskeletons to support specific industrial jobs, barriers to adoption still exist. Contextual factors underlying exoskeleton adoption need further understanding. Purpose: We aimed to document how stakeholder perceptions of exoskeleton technologies could be affected by physical exposure to a wide variety of exoskeletons, by providing an opportunity to wear them and perform standardized tasks. Methods: We recorded the opinions of 22 participants from different manufacturing industries, both before and after trying seven different passive arm-support and back-support occupational EXOs. EXO expectations, adoption factors/barriers in their work settings, and perceived next steps for implementing such technologies were captured. Participants also completed usability questionnaires after each EXO trial. Results: Even brief exposure to EXOs positively influenced both worker and stakeholder perceptions on exoskeleton usefulness and safety; in contrast, worker concerns about usability and acceptability remained unchanged. Participants indicated stronger preferences for some specific EXO technologies, in terms of ease of use, performance improvements, and applicability. Conclusions: Actual exposure to occupational exoskeletons, even if brief, was found to alter worker and stakeholder perceptions of exoskeleton usefulness and safety. Future work on technology perceptions and intention to use exoskeletons may need to consider physical exposure to devices before soliciting perceptions, especially for novel technologies like exoskeletons.

Three passive arm-support exoskeletons have inconsistent effects on muscle activity, posture, and perceived exertion during diverse simulated pseudo-static overhead nutrunning tasks.

Arm-support exoskeletons (ASEs) are an emerging technology with the potential to reduce physical demands during diverse tasks, especially overhead work. However, limited information is available about the effects of different ASE designs during overhead work with diverse task demands. Eighteen participants (gender-balanced) performed lab-based simulations of a pseudo-static overhead task. This task was performed in six different conditions (3 work heights × 2 hand force directions), with each of three ASEs and in a control condition (i.e., no ASE). Using ASEs generally reduced the median activity of several shoulder muscles (by ∼12-60%), changed working postures, and decreased perceived exertion in several body regions. Such effects, though, were often task-dependent and differed between the ASEs. Our results support earlier evidence of the beneficial effects of ASEs for overhead work but emphasize that: 1) these effects depend on the task demands and ASE design and 2) none of the ASE designs tested was clearly superior across the tasks simulated.

A pilot study investigating motor adaptations when learning to walk with a whole-body powered exoskeleton.

Evidence is emerging on how whole-body powered exoskeleton (EXO) use impacts users in basic occupational work scenarios, yet our understanding of how users learn to use this complex technology is limited. We explored how novice users adapted to using an EXO during gait. Six novices and five experienced users completed the study. Novices completed an initial training/familiarization gait session, followed by three subsequent gait sessions using the EXO, while experienced users completed one gait session with the EXO. Spatiotemporal gait measures, pelvis and lower limb joint kinematics, muscle activities, EXO torques, and human-EXO interaction forces were measured. Adaptations among novices were most pronounced in spatiotemporal gait measures, followed by joint kinematics, with smaller changes evident in muscle activity and EXO joint torques. Compared to the experienced users, novices exhibited a shorter step length and walked with significantly greater anterior pelvic tilt and less hip extension. Novices also used lower joint torques from the EXO at the hip and knee, and they had greater biceps femoris activity. Overall, our results may suggest that novices exhibited clear progress in learning, but they had not yet adopted motor strategies similar to those of experienced users after the three sessions. We suggest potential future directions to enhance motor adaptations to powered EXO in terms of both training protocols and human-EXO interfaces.

A novel approach to quantify the assistive torque profiles generated by passive back-support exoskeletons.

Industrial exoskeletons are a promising ergonomic intervention to reduce the risk of work-related musculoskeletal disorders by providing external physical support to workers. Passive exoskeletons, having no power supplies, are of particular interest given their predominance in the commercial market. Understanding the mechanical behavior of the torque generation mechanisms embedded in passive exoskeletons is, however, essential to determine the efficacy of these devices in reducing physical loads (e.g., in manual material handling tasks). We introduce a novel approach using a computerized dynamometer to quantify the assistive torque profiles of two passive back-support exoskeletons (BSEs) at different support settings and in both static and dynamic conditions. The feasibility of this approach was examined using both human subjects and a mannequin. Clear differences in assistive torque magnitudes were evident between the two BSEs, and both devices generated more assistive torques during trunk/hip flexion than extension. Assistive torques obtained from human subjects were often within similar ranges as those from the mannequin, though values were more comparable over a narrow range of flexion/extension angles due to practical limitations with the dynamometer and human subjects. Characterizing exoskeleton assistive torque profiles can help in better understanding how to select a torque profile for given task requirements and user anthropometry, and aid in predicting the potential impacts of exoskeleton use by incorporating measured torque profiles in a musculoskeletal modeling system. Future work is recommended to assess this approach for other occupational exoskeletons.

Task demand and load carriage experience affect gait variability among military cadets.

Load carriage is an inevitable daily task for soldiers. The purposes of this study were to explore the extent to which gait variability (GV) is affected by load carriage and experience among military cadets, and whether experience-related differences in GV are dependent on task demand. Two groups of cadets (30 experienced, 30 less experienced) completed a load carriage task in each of three load conditions (no load, 16 kg, 32 kg). Three categories of GV measures were obtained: spatiotemporal variability, joint kinematic variability, and Lyapunov exponents. Compared to traditional mean gait measures, GV measures were more discriminative of experience: although both groups showed similar mean gait measures, the experienced participants had reduced variability in spatiotemporal measures (p ≤ 0.008) and joint kinematics (p ≤ 0.004), as well as lower levels of long-term local dynamic stability at the ankle (p = 0.040). In both groups, heavier loads were also caused increased GV (p ≤ 0.018) and enhanced short-term local dynamic stability at the knee (p = 0.014). These results emphasize the importance of GV measures, which may provide a more complete description of adaptability, stability, and control; highlight alternate movement strategies during more difficult load carriage; and capture experience-related differences in load carriage strategies.

Wearing a back-support exoskeleton impairs single-step balance recovery performance following a forward loss of balance - An exploratory study.

Back-support exoskeletons (BSEs) are a promising ergonomic intervention for reducing physical demands on the low-back, but little is known regarding whether BSE use alters balance recovery following external perturbations. Hence, we investigated the effects of wearing a BSE on single-step balance recovery following a forward loss of balance. Sixteen (8 M, 8F) young, healthy participants were released from static forward-leaning postures and attempted to recover their balance with a single step while wearing a BSE (backXTM) with three different levels of support torque (i.e., no torque, low, and high) and in a control condition (no exoskeleton). Lean angle was increased until they failed in two consecutive trials to recover their balance with a single step. The maximum lean angle from which individuals could successfully recover was not significantly altered when wearing the BSE. However, wearing the BSE under all torque conditions increased reaction times. The BSE also impeded hip flexion (i.e., decrease in both peak hip flexion angle and angular velocity), resulting in decreased peak knee flexion velocity, knee range of motion, and step length. Measures of the margin of stability decreased significantly in the high-torque BSE condition. Overall, our results suggest that use of a BSE that provides external hip extension torque impairs balance recovery responses. Future work extending kinetic analyses to recovery responses, as well as a study of recovery when responding to slips and trips while walking, would offer a more complete picture of how a BSE may impact balance recovery following a loss of balance.

Fall impacts from standing show equivalence between experts in stage combat landing strategy and naïve participants after training.

BACKGROUND: Slips, trips, and falls are the second leading cause of non-fatal injuries in workplace in the United States. A stage combat landing strategy is used in the theatre arts to reduce the risk of fall-induced injury, and may be a viable approach among some working populations. OBJECTIVE: The goal of this study was to compare fall impact characteristics between experts in stage combat landing strategy and naïve participants after four training sessions of stage combat landing strategy training. METHODS: Forward and backward falls from standing were induced by releasing participants from static leans. Participants fell onto a foam mat, and impact force was measured using force platforms under the mat. A statistical equivalence test was used to determine if impact characteristics between groups were similar. RESULTS: Results indicated equivalence between groups in peak impact force during backward but not forward falls. Equivalence between groups in impact time suggested a mechanism by which equivalence in peak impact force as achieve. CONCLUSIONS: Four training sessions was sufficient for naïve participants to exhibit fall impact characteristics similar to experts in an anecdotally-effective landing strategy, and support further study. To our knowledge, this was the first study to investigate training for a landing strategy involving stepping after losses of balance from standing.

Effects of Back-Support Exoskeleton Use on Lower Limb Joint Kinematics and Kinetics During Level Walking.

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.

Effects of using a whole-body powered exoskeleton during simulated occupational load-handling tasks: A pilot study.

Whole-body powered exoskeletons (WB-PEXOs) can be effective in reducing the physical demands of heavy occupational work, yet almost no empirical evidence exists on the effects of WB-PEXO use. This study assessed the effects of WB-PEXO use on back and leg muscle activities during lab-based simulations of load handling tasks. Six participants (4M, 2F) completed two such tasks (load carriage and stationary load transfer), both with and without a WB-PEXO, and with a range of load masses in each task. WB-PEXO use reduced median levels of muscle activity in the back (∼42-53% in thoracic and ∼24-43% in lumbar regions) and legs (∼41-63% in knee flexors and extensors), and mainly when handling loads beyond low-moderate levels (10-15 kg). Overall, using the WB-PEXO also reduced inter-individual variance (smaller SD) in muscle activities. Future work should examine diverse users, focus on finding effective matches between WB-PEXO use and specific tasks, and identify applications in varied work environments.

Effects of back-support exoskeleton use on gait performance and stability during level walking.

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.