Robotic ankle exoskeletons have the potential to extend human ability, and actuation timing serves as one of the critical parameters in its controller design. While many experiments have investigated ...the optimal actuation timing values to achieve different objective functions ( e.g. minimizing metabolic cost), studies on users' perception of control parameters are gaining interest as it gives information on people's comfort, coordination, and trust in using devices, as well as providing foundations on how the sensorimotor system detects the exoskeleton behavior changes. The purpose of this study was to evaluate people's sensitivity to changes in exoskeleton actuation timing and its associated exoskeleton ankle angle changes during walking. Participants (n =15) with little or no prior experience with ankle exoskeletons were recruited and performed a psychophysical experiment to characterize their just-noticeable difference (JND) thresholds for actuation timing. Participants wore a bilateral active ankle exoskeleton and compared pairs of torque profiles with different actuation timings and low peak torque (0.225 Nm/kg) while walking on the treadmill. The mean timing JND across participants was 2.8±0.6% stride period. Individuals exhibited different sensitivity towards actuation timing, and their associated exoskeleton ankle angle changes also varied. The variance in ankle angle changes might be explained by their differences in ankle stiffness and different ankle torques provided during walking. The results provide insights into how people perceive the changes in exoskeleton control parameters and show individual differences in exoskeleton usage. The actuation timing JND found in this study can also help determine the necessary controller precision.
Surface electromyography (sEMG) may not be a simple 1,2,3 (muscle, electrodes, signal)-step operation. Lists of sEMG characteristics and applications have been extensively published. All point out ...the noise mimicking perniciousness of the sEMG signal. This has resulted in ever more complex manipulations to interpret muscle functioning and sometimes gobbledygook. Hence, as for all delicate but powerful tools, sEMG presents challenges in terms of precision, knowledge, and training. The theory is usually reviewed in courses concerning sensorimotor systems, motor control, biomechanics, ergonomics, etc., but application requires creativity, training, and practice. Software has been developed to navigate the essence extraction (step 4); however, each software requires some parametrization, which returns back to the theory of sEMG and signal processing. Students majoring in Ergonomics or Biomedical Engineering briefly learn about the sEMG method but may not necessarily receive extensive training in the laboratory. Ergonomics applications range from a simple estimation of the muscle load to understanding the sense of effort and sensorimotor asymmetries. In other words, it requires time and the basics of multiple disciplines to acquire the necessary knowledge and skills to perform these studies. As an example, sEMG measurements of left/right limb asymmetries in muscle responses to vibration-induced activity of proprioceptive receptors, which vary with gender, provide insight into the functioning of sensorimotor systems. Beyond its potential clinical benefits, this example also shows that lack of testing time and lack of practitioner's sufficient knowledge are barriers to the utilization of sEMG as a clinical tool.
Exoskeletons have the potential to assist users and augment physical ability. To achieve these goals across users, individual variation in muscle activation patterns when using an exoskeleton need to ...be evaluated. This study examined individual muscle activation patterns during walking with a powered ankle exoskeleton. 60% of the participants were observed to reduce medial gastrocnemius activation with exoskeleton powered and increase with the exoskeleton unpowered during stance. 80% of the participants showed a significant increase in tibialis anterior activation upon power addition, with inconsistent changes upon power removal during swing. 60% of the participants that were able to adapt to the system, did not de-adapt after 5 min. Muscle activity patterns differ between individuals in response to the exoskeleton power state, and affected the antagonist muscle behavior during this early adaptation. It is important to understand these different individual behaviors to inform the design of exoskeleton controllers and training protocols.
•Muscle activation patterns differ between users during initial exoskeleton walking.•Exoskeleton actuation during stance can influence muscle activation during swing.•Training procedures are needed to encourage specific muscle recruitment strategies.•Participants that were able to adapt did not necessarily de-adapt to the system.•Caution should be taken when interpreting co-activation and co-contraction index.
•Larger absolute error for older than younger adults.•Larger position matching errors with the left non-dominant forearm for older adults.•A disparate position sense asymmetry (absence of asymmetry) ...for older adults.•Profiles of illusory movement matching differed between younger and older adults.•No significant asymmetry in movement perception for older adults.
Age-related differences in proprioceptive asymmetries have received little attention. This study aimed to determine differences in asymmetry of the right/left upper limb proprioceptive systems between younger and older adults. Asymmetries were compared in two “eyes closed” experiments involving the same elbow joints. Position sense was tested in two matching conditions: ipsilateral remembered and contralateral concurrent. Movement sense was tested while reproducing with the opposite forearm the illusory movement elicited by distal tendon vibration applied to the reference forearm. Older adults exhibited a larger error when matching with the non-dominant than dominant forearm in the ipsilateral remembered condition and a disparate asymmetry in the contralateral condition when compared to younger adults. In addition, in older adults, the velocity of reproduced illusory movements was slower, and asymmetry in movement perception was not significant. The difference in proprioceptive asymmetry between younger and older adults might be attributed to a significant reduction of the sensory system gain affecting, more particularly, the left non-dominant arm sensory system via several physiological and neurophysiological mechanisms.
Although previous studies have shown that powered exoskeletons reduce muscle activation while walking across participants, less is known about how they impact an individual’s muscle activation. This ...study examined an individual’s muscle activity during walking with a powered ankle exoskeleton. The designed human-exoskeleton coordination was defined as a decrease in medial gastrocnemius (MGAS) muscle activation with the exoskeleton powered and increase with the exoskeleton unpowered. 60% of the participants were observed to coordinate with the exoskeleton as designed, with 67% showing a decrease in RMS MGAS during adaptation. 60% of the participants showed no change during the de-adaptation, with 47% not returning to baseline metrics by late de-adaptation. Muscle activity differs between individuals in response to the exoskeleton power state and over time within the power state. It is important to consider these different behaviors when integrating exoskeletons into occupational settings as adaptation may be supported by training and experience.
Hand-arm vibration (HAV), which potentially causes vibration white finger (VWF), and occupational noise are serious issues in the agricultural and forestry industries. Generally, agricultural workers ...operate as single-family/small businesses and thus are exempted from Occupational Safety and Health Administration (OSHA) regulations/laws for noise and HAV otherwise applicable to other industries in general. The agricultural/forestry sectors are at increased risk as working hours are longer than a typical 8-h work shift putting them at greater risk of hearing loss. The study was conducted to assess the possible association between hearing sensitivity on combined exposure to noise and hand-arm vibration. A systematic literature review was conducted on exposure to noise and HAV in the agricultural/forestry sector and the resulting impacts on hearing. The peer-reviewed articles in English were searched with 14 search words in three databases of PubMed, Ergo Abstracts, and Web of Science without any filter for the year for fully available article text. The database literature search resulted in 72 articles. Forty-seven (47) articles met the search criteria based on the title. Abstracts were then reviewed for any relationship between hearing loss and hand-arm vibration/Raynaud's phenomenon/VWF. This left 18 articles. It was found that most agricultural workers and chainsaw workers are exposed to noise and VWF. Hearing is impacted by both noise and aging. The workers exposed to HAV and noise had greater hearing loss than non-exposed workers, possibly due to the additive effect on temporary threshold shift (TTS). It was found that VWF might be associated with vasospasm in the cochlea through autonomous vascular reflexes, digital arteries narrowing, vasoconstriction in the inner ear by noise, ischemic damage to the hair cells and increased oxygen demand, which significantly affects the correlation between VWF and hearing loss.
(1) Background: The objectives of this systematic review were to (i) summarize the results of studies evaluating the reliability of observational ergonomics exposure assessment tools addressing ...exposure to physical risk factors associated with upper extremity musculoskeletal disorders (MSDs), and (ii) identify best practices for assessing the reliability of new observational exposure assessment tools. (2) Methods: A broad search was conducted in March 2020 of four academic databases: PubMed, Science Direct, Ergonomic Abstracts, and Web of Science. Articles were systematically excluded by removing redundant articles, examining titles and abstracts, assessing relevance to physical ergonomics and the upper extremities, and article type. (3) Results: Eleven articles were included in the review. The results indicated no singular best practice; instead, there were multiple methodological approaches researchers chose to use. Some of the significant variations in methodologies include the selection of reliability coefficients, rater and participant selection, and direct vs. digital observation. (4) Conclusion: The findings serve as a resource summarizing the reliability of existing observational risk assessment tools and identify common methods for assessing the reliability of new observational risk assessment tools. Limitations of this review include the number of databases searched, the removal of truncation symbols, and the selection of keywords used for the initial search.
Measuring the physical demands of work is important in understanding the relationship between exposure to these job demands and their impact on the safety, health, and well-being of working people. ...However, work is changing and our knowledge of job demands should also evolve in anticipation of these changes. New opportunities exist for noninvasive long-term measures of physical demands through wearable motion sensors, including inertial measurement units, heart rate monitors, and muscle activity monitors. Inertial measurement units combine accelerometers, gyroscopes, and magnetometers to provide continuous measurement of a segment's motion and the ability to estimate orientation in 3-dimensional space. There is a need for a system-thinking perspective on how and when to apply these wearable sensors within the context of research and practice surrounding the measurement of physical job demands. In this paper, a framework is presented for measuring the physical work demands that can guide designers, researchers, and users to integrate and implement these advanced sensor technologies in a way that is relevant to the decision-making needs for physical demand assessment. We (i) present a literature review of the way physical demands are currently being measured, (ii) present a framework that extends the International Classification of Functioning to guide how technology can measure the facets of work, (iii) provide a background on wearable motion sensing, and (iv) define 3 categories of decision-making that influence the questions that we can ask and measures that are needed. By forming questions within these categories at each level of the framework, this approach encourages thinking about the systems-level problems inherent in the workplace and how they manifest at different scales. Applying this framework provides a systems approach to guide study designs and methodological approaches to study how work is changing and how it impacts worker safety, health, and well-being.
Stroke is known to degrade sensory and/or motor processes. This research aimed to assess the functioning of the sensory and motor components of each upper limb/hemisphere system of mild to moderate ...stroke patients to determine the primary source of impairment. The hypothesis was that individualized specific training (sensory vs. motor) favor the recovery of functional abilities. Sensory and motor alterations, induced by unilateral mild to moderate stroke and aging, were investigated separately. For the sensory system, a 20 degrees elbow flexion reference position was matched with the same or opposite arm, and vibration-induced movement illusion was matched with the opposite arm. For the motor system, an isometric 20% MVC reference elbow extension effort was matched with the same or opposite arm, and an isometric force tracking task was performed with each arm. The same protocols and procedures were used in all studies. The first study investigated the left and right proprioceptive sensory and motor systems in younger and older younger adults. Age was found to induce a decrease in the gain of both systems, transforming asymmetries of position sense, movement sense and sense of effort, as well as force control. The second study investigated the left and right proprioceptive sensory systems in stroke patients. The asymmetry in elbow joint position sense was exacerbated, and attenuation of proprioceptive sensitivity was found when compared to older adults. The third study investigated the alteration of the right and left motor systems in stroke patients. The gain transformation produced by stroke corresponded to an exacerbation of age effects, especially for the affected arm. The last study investigated whether impairment-specific training (proprioceptive vs. motor) improves sensory and/or motor deficits in stroke patients after the identification of their primary deficit. Stroke patients were divided into two groups based on studies 1 and 2 assessments: primary sensory or motor deficit was assigned to corresponding impairment-specific training. A reaching functional task to a small target and training to reproduced with the same arm a reference position or extension effort were performed with the affected arm. The respective deficits observed in studies 1 and 2 were reassessed using the same protocols, respectively. Adaptation of training to the primary deficit leads to functional and sensory or motor improvement for the affected side for 60% of the patients. Although 40% of the patients also showed improvement in some tasks, sensory and/or motor training only was not sufficient, as indicated by limited improvement in the functional task. These results lead us to suggest that (1) age and stroke contributes to alterations in position sense, movement sense, sense of effort and force control that may result from the combination of the structural and neurophysiological reorganization of cortical and, likely, other brain structures, which lead to changes in behaviors, (2) alterations can be viewed as conferring a different gain to the sensory and/or motor systems that transform intrinsic natural asymmetries, which should be considered in rehabilitation, (3) the differentiation of stroke-induced sensory and motor deficits is possible, and (4) recovery by impairment-specific training is positive for the corresponding system in patients but has limited effects when both sensory and motor systems are affected, which appears to be related to stroke severity. The results also indicated that the affected side and handedness are factors to consider in the individualization/adaptation of rehabilitation procedures.
Actuation timing is an important parameter in powered ankle exoskeleton control that can significantly influence user experience and human-system performance. Previous studies have investigated the ...actuation timing through optimization under different objective functions, such as minimizing metabolic cost. However, little is known about people's psychological sense of actuation timing. This pilot study measured two subjects' sensitivity to small changes in actuation timing during walking. The just-noticeable difference (JND) threshold was determined via a fitted psychometric function, which quantified subjects' performance in discriminating between a pair of actuation timings. Subjects could detect changes of 3.6% and 6.8% stride period in actuation timing respectively, showing the difference in perception between individuals. The results from this pilot study provide a preliminary understanding of human perception towards exoskeleton control parameters, which offers insight on individual differences in exoskeleton usage and informs exoskeleton precision requirements to minimize undesired human-system interaction.
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