Human pressure tolerance and effects of different padding materials with implications for development of exoskeletons and similar devices

Elastic textile-based wearable modulation of musculoskeletal load: A comprehensive review of passive exosuits and resistance clothing

Elastic textiles play a critical role in passive wearable solutions for musculoskeletal load management in both passive exosuits and resistance clothing. These textiles, based on their ability to stretch and retract, can exhibit ambivalence in their load-modulating effects when used in occupational, rehabilitation, exercise, or everyday activity settings. While passive exosuits and resistance garments may appear similar in design, they have opposing goals: to reduce the musculoskeletal load in the case of exosuits and to increase it in the case of resistance clothing. Despite this intrinsic connection, these two approaches have not been extensively linked together. This review aims to fill this gap by examining the common and distinct principles of elastic textiles in passive exosuits and resistance clothing, shedding light on their interactions and the complex dynamics of musculoskeletal load systems. The effectiveness of different designs in passive exosuits that mimic musculoskeletal function and resistance clothing that increase the workload for strength training are critically reviewed. Current challenges in practical implementation and opportunities to improve critical issues, such as preload, thermal comfort, skin friction, and donning and doffing are also highlighted.

A comprehensive assessment of a passive back support exoskeleton for load handling assistance

Various back support exoskeletons (BSEs) have been developed to reduce the workload and the risk of musculoskeletal disorders. However, the evaluations of such devices have primarily focused on specific quantitative aspects like muscle activation level or metabolic cost without any assessment of the user perception or comfort. In addition, the absence of an universal guidance or agreement on the methods for quantifying the efficacy of exoskeletons has hampered a systematic comparison among the developed devices. This study introduces a newly developed passive BSE for heavy load handling workers, and verifies its assistive effect through a rigorous and multifaceted evaluation. Fifteen young and healthy males participated in two experiment sessions. In the first session, participants lifted a 15 kg box and held it in a static position. In the second session, participants performed repetitive lifting tasks with a 10 kg box. The developed BSE reduced root mean square, peak, and integrated muscle activation with statistical significance in the key muscles. The BSE alleviated muscle fatigue by delaying spectral shift of instantaneous median frequency in the lumbar erector spinae (p < 0.001) and gluteus maximus (p < 0.001). The BSE also decreased energy expenditure by 13.6% (p < 0.001). In addition, the BSE reduced participants' rate of perceived exertion and local musculoskeletal discomfort by 14.7% (p = 0.005) and 30.5% (p = 0.001), respectively. These results support the efficacy of the developed BSE. The multifaceted evaluation process used in this study also contributes to proposing a systematic guidance on evaluating BSEs.

The effects of soft vs. rigid back-support exoskeletons on trunk dynamic stability and trunk-pelvis coordination in young and old adults during repetitive lifting

While back-support exoskeletons are increasing in popularity as an ergonomic intervention for manual material handling, they may cause alterations to neuromuscular control required for maintaining spinal stability. This study evaluated the effects of soft and rigid passive exoskeletons on trunk local dynamic stability and trunk-pelvis coordination. Thiry-two young (18-30 years) and old (45-60 years) men and women completed repetitive lifting and lowering tasks using two different exoskeletons and in a control condition. Both exoskeletons significantly reduced the short-term maximum Lyapunov exponent (LyE) of the trunk (p < 0.01), suggesting improved local dynamic stability. There was also a significant main effect of age (p = 0.05): older adults exhibited lower short-term LyE that young adults. Use of the soft exoskeleton significantly increased, while the rigid exoskeleton significantly decreased, long-term LyE, and these changes were more pronounced in the young group compared to the old group. Additionally, exoskeleton use resulted in significant increase (p < 0.001) of mean absolute relative phase (MARP) and deviation phase (DP) by ∼30-60 %, with greater increases due to the rigid than the soft device. Thus, trunk-pelvic coordination and coordination variability were negatively impacted by exoskeleton use. Potential reasons for these findings may include exoskeleton-induced changes in lifting strategy, reduced peak trunk flexion velocity, and cycle-to-cycle variability of trunk velocity. Furthermore, although the soft and rigid devices caused comparable changes in trunk-extensor muscle activity, they exhibited differential effects on long-term maximum Lyapunov exponents as well as trunk-pelvic coordination, indicating that exoskeleton design features can have complex effects on trunk neuromuscular control.

Advances in active knee brace technology: A review of gait analysis, actuation, and control applications

This article discusses the significance of knee joint mechanics and the consequences of knee dysfunctions on an individual's quality of life. The utilization of active knee braces, which incorporate concepts of mechatronics systems, is investigated here as a potential treatment option. The complexity of the construction of the knee joint, which has six degrees of motion and is more prone to injury since it bears weight, is emphasized in this article. By wearing braces and using other support devices, one's knee can increase stability and mobility. In addition, the paper discusses various technologies that can be used to measure the knee adduction moment and supply spatial information on gait. Actuators for active knee braces must be compact, lightweight, and capable of producing a significant amount of torque; as a result, electric, hydraulic, and pneumatic actuators are the most common types. Creating control mechanisms, such as position control techniques and force/torque control approaches, is essential to knee exoskeleton research and development. These methods might make knee joint rehabilitation and assistive technology safer and more effective.

In-ear earphone design-oriented pressure sensitivity evaluation on the external ear

This study aimed to explore the pressure sensitivity of the external ear that can be the basis for adapting the pressure distribution on the concha for in-ear earphone design. Overall, 30 participants were included in this study, where an electronic mechanical algometer with a stepping motor was used to apply constant pressure. Before the experiment, the customised concha shell models of the participants were positioned in the ear perpendicular to the concha surface. Furthermore, the pressure discomfort threshold (PDT), moderate pressure discomfort (MPD), and maximum pressure threshold (MPT) in eight regions of the ear were recorded. This study's results indicate that the four regions of the external ear are less sensitive to pressure than those of the other regions. Additionally, women had higher pressure sensitivity values in the external ear. Therefore, this study's findings could have important implications for earphone designs and evaluating discomfort conditions in the external ear. Practitioner summary: This study explores the pressure sensitivity threshold (PDT, MPD, and MPT) on the external ear and the relevant implications for in-ear earphone design. Interestingly, regions closer to the bone structure were less sensitive to pressure, and men could tolerate greater pressure on the external ear than women.

Evaluation Methods and Measurement Challenges for Industrial Exoskeletons

In recent years, exoskeleton test methods for industrial exoskeletons have evolved to include simulated laboratory and field environments. Physiological, kinematic, and kinetic metrics, as well as subjective surveys, are used to evaluate exoskeleton usability. In particular, exoskeleton fit and usability can also impact the safety of exoskeletons and their effectiveness at reducing musculoskeletal injuries. This paper surveys the state of the art in measurement methods applied to exoskeleton evaluation. A notional classification of the metrics based on exoskeleton fit, task efficiency, comfort, mobility, and balance is proposed. In addition, the paper describes the test and measurement methods used in supporting the development of exoskeleton and exosuit evaluation methods to assess their fit, usability, and effectiveness in industrial tasks such as peg in hole, load align, and applied force. Finally, the paper includes a discussion of how the metrics can be applied towards a systematic evaluation of industrial exoskeletons, current measurement challenges, and future research directions.

Industrial exoskeletons for overhead work: Circumferential pressures on the upper arm caused by the physical human-machine-interface

This study investigated the pressures occurring within the arm human-machine-interfaces (HMI) of four different exoskeletons that support static and dynamic work at or above head level, and the effects of the HMI on neurovascular supply of the upper extremity using an orthopedic provocation maneuver with raised arms with and without the exoskeletons. Decreased time in the provocation maneuver with exoskeletons indicated a negative effect of the HMIs on the vascular and neural supply of the arm. Average pressure in the static situation was 3.2 ± 0.7 kPa and 4.4 ± 0.4 kPa with regular peak values of 6.5 ± 0.5 kPa in the dynamic task. These pressures were significantly higher than the pressure values that guarantee adequate tissue oxygenation. It remains unknown whether the way exoskeletons apply pressure affects vascular and neural supply to the arms, or whether the regular unloading during dynamic activity has a neutralizing effect.

An Integrated Dynamic Closed Loop Simulation Platform for Elbow Flexion Augmentation Using an Upper Limb Exosuit Model

Wearable robotic devices are designed to assist, enhance or restore human muscle performance. Understanding how a wearable robotic device changes human biomechanics through complex interaction is important to guide its proper design, parametric optimization and functional success. The present work develops a human-machine-interaction simulation platform for closed loop dynamic analysis with feedback control and to study the effect of soft-robotic wearables on human physiology. The proposed simulation platform incorporates Computed Muscle Control (CMC) algorithm and is implemented using the MATLAB -OpenSim interface. The framework is generic and will allow incorporation of any advanced control strategy for the wearable devices. As a demonstration, a Gravity Compensation (GC) controller has been implemented on the wearable device and the resulting decrease in the joint moments, muscle activations and metabolic costs during a simple repetitive load lifting task with two different speeds is investigated.

Usability, User Acceptance, and Health Outcomes of Arm-Support Exoskeleton Use in Automotive Assembly: An 18-month Field Study

OBJECTIVE

Examine arm-support exoskeleton (ASE) user experience over time, identify factors contributing to ASE intention-to-use, and explore whether ASE use may influence the number of medical visits.

METHODS

An 18-month, longitudinal study with ASE (n = 65) and control groups (n = 133) completed at nine automotive manufacturing facilities.

RESULTS

Responses to six usability questions were rather consistent over time. ASE use perceived effective in reducing physical demands on the shoulders, neck, and back. Perceived job performance, and overall fit and comfort, appeared to be key determinants for ASE intention-to-use. Based on medical visits among both groups, ASE use may decrease the likelihood of such visits.

CONCLUSIONS

These field results support the potential of ASEs as a beneficial ergonomic intervention, but also highlight needs for further research on ASE designs, factors driving intention-to-use, and health outcomes.

Exoskeletons and Exosuits Could Benefit from Mode-Switching Body Interfaces That Loosen/Tighten to Improve Thermal Comfort

Exoskeletons and exosuits (exos) are wearable devices that physically assist movement. User comfort is critically important for societal adoption of exos. Thermal comfort (a person's satisfaction with their thermal environment) represents a key design challenge. Exos must physically attach/interface to the body to apply forces, and these interfaces inevitably trap some heat. It is envisioned that thermal comfort could be improved by designing mode-switching exo interfaces that temporarily loosen around a body segment when assistive forces are not being applied. To inform exo design, a case series study (N = 4) based on single-subject design principles was performed. Our objective was to assess individual responses to skin temperature and thermal comfort during physical activity with a Loose leg-sleeve interface compared with a Form-Fitting one, and immediately after a Form-Fitting sleeve switched to Loose. Skin under the Loose sleeve was 2-3 °C (4-6 °F) cooler after 25 min of physical activity, and two of four participants reported the Loose sleeve improved their thermal comfort. After completion of the physical activity, the Form-Fitting sleeve was loosened, causing a 2-4 °C (3-8 °F) drop in skin temperature underneath for all participants, and two participants to report slightly improved thermal comfort. These findings confirmed that an exo that can quickly loosen its interface when assistance is not required-and re-tighten when it is- has the potential to enhance thermal comfort for some individuals and environments. More broadly, this study demonstrates that mode-switching mechanisms in exos can do more than adjust physical assistance: they can also exploit thermodynamics and facilitate thermoregulation in a way that enhances comfort for exo users.

Challenges and solutions for application and wider adoption of wearable robots

The science and technology of wearable robots are steadily advancing, and the use of such robots in our everyday life appears to be within reach. Nevertheless, widespread adoption of wearable robots should not be taken for granted, especially since many recent attempts to bring them to real-life applications resulted in mixed outcomes. The aim of this article is to address the current challenges that are limiting the application and wider adoption of wearable robots that are typically worn over the human body. We categorized the challenges into mechanical layout, actuation, sensing, body interface, control, human-robot interfacing and coadaptation, and benchmarking. For each category, we discuss specific challenges and the rationale for why solving them is important, followed by an overview of relevant recent works. We conclude with an opinion that summarizes possible solutions that could contribute to the wider adoption of wearable robots.

Effectiveness of Soft versus Rigid Back-Support Exoskeletons during a Lifting Task

This study investigated the influence of passive back-support exoskeletons (EXO_BK) design, trunk sagittal inclination (TSI), and gender on the effectiveness of an exoskeleton to limit erector spinae muscle (ES) activation during a sagittal lifting/lowering task. Twenty-nine volunteers performed an experimental dynamic task with two exoskeletons (two different designs: soft (SUIT) and rigid (SKEL)), and without equipment (FREE). The ES activity was analyzed for eight parts of TSI, each corresponding to 25% of the range of motion (lifting: P1 to P4; lowering: P5 to P8). The impact of EXO_BK on ES activity depended on the interaction between exoskeleton design and TSI. With SKEL, ES muscle activity significantly increased for P8 (+36.8%) and tended to decrease for P3 (−7.2%, p = 0.06), compared to FREE. SUIT resulted in lower ES muscle activity for P2 (−9.6%), P3 (−8.7%, p = 0.06), and P7 (−11.1%), in comparison with FREE. Gender did not influence the effect of either back-support exoskeletons on ES muscle activity. These results point to the need for particular attention with regard to (1) exoskeleton design (rigid versus soft) and to (2) the range of trunk motion, when selecting an EXO_BK. In practice, the choice of a passive back-support exoskeleton, between rigid and soft design, requires an evaluation of human-exoskeleton interaction in real task conditions. The characterization of trunk kinematics and ranges of motion appears essential to identify the benefits and the negative effects to take into account with each exoskeleton design.