Significance and Use
4.1 Improperly fitted exoskeletons may cause discomfort, distraction, stress, disuse, accidents, and therefore, may cause unacceptable risk of injury or damage to the health of users (1).5 An improperly fitted exoskeleton can also cause a loss of cognitive fit and task failure. According to Ref (2), “Cognitive fit refers to supporting the perception–cognition–action decision process of the human when wearing the exosystem.” This characteristic is relevant to exosystem fit as the operator’s cognitive capability must be maintained such that operational tasks, including decision making, can be adequately performed. Thus, manufacturers and designers may consider user anthropometry and fit when designing exoskeletons. This guide provides a set of recommendations for considering the anthropometry (body size and shape) of the intended user population of an exoskeleton. These recommendations can provide guidance to designers on fit criteria. They will also facilitate the consistent (repeatable) estimation of accommodation rates. This guide further highlights important considerations in the design of exoskeletons which are impacted by human physical variation as well as range of motion and clearances, which are critical safety concerns. Additionally, anthropometric considerations also extend to kinematic and kinetic parameters; however, these concepts are beyond the scope of this guide. Lastly, this guide assumes the reader understands the fundamentals behind anthropometry and human biomechanics.
4.1.1 In estimating how much (that is, what percentage) of the population is accommodated by an exoskeleton, it is critical to use the appropriate anthropometric database. The anthropometric data upon which the design is based should match the target user population as closely as possible. This can be a challenge, particularly for civilian populations where detailed anthropometric data are often not widely available. A list of readily available anthropometric databases is provided in Appendix X1. A limited number of civilian datasets are available in the public domain (that is, free). There are more extensive anthropometric datasets that are available for purchase.
4.1.2 When discussing accommodation, disproportionate disaccommodation is an essential conversation in the context of groups not considered. Disproportionate disaccommodation occurs when one group (for example, men) is accommodated at a rate different than that of other groups (for example, women) or at rates different than their relative presence in the overall population. Best practices of estimating fit include consideration of available anthropometric data and attention to sub-populations that may not be fully accommodated.
4.2 Considering anthropometry during exoskeleton design will result in information useful to end users. Information may include who may safely and effectively use an exoskeleton and how to correctly measure body dimensions to determine size requirements. Sizing information may also include criteria to determine if the exoskeleton is fitting properly and how to adjust the exoskeleton for a better fit. Possible limitations to the end user’s range of motion and guidance regarding the use of clothing, PPE, or other equipment may also be provided to the end user.
4.3 Not every element of this guide may be applicable to all exoskeletons, nor are the recommendations in this guide intended to be prescriptive (that is, manufacturers may already provide a variable level of adjustability inherent in the exoskeleton design which may be described in their guidance).
4.4 Static and dynamic fit are related to, but not the same as, comfort. Static fit refers to the alignment between dimensions of the human and exoskeleton in one or a small number of predefined, standardized postures, with no consideration of movement. An example of static fit is a user in a standing posture with their hands by their side. This would allow for shoulder breadth measurements to be taken. Dynamic fit, on the other hand, relates to the fit of the human and exoskeleton interaction with each other through functional range of motion (ROM) activities. An example of dynamic fit is a user moving the shoulder complex through the range of motion for flexion/extension and adduction/abduction. This would allow for changes in the shoulder complex to be noted and measured.
4.4.1 The environment is an important factor in dealing with evaluations of comfort or discomfort. According to Ref (3), discomfort was reported to be related to the physical characteristics of an environment. However; in the absence of discomfort, the user experiences a neutral subjective state. To notice comfort, something positive may be experienced, such as rest, security, relaxation, or indulgence; therefore, comfort and discomfort are considered two independent constructs. Nevertheless, in equipment evaluation, both discomfort and comfort can be related to an equipment’s physical features (4, 5), albeit, comfort may also include the visual pleasure of a design as well (6, 7). For example, when wearing an exoskeleton, fit is a parameter of the exoskeleton. However, if the exoskeleton does not fit from an anthropometric perspective, this could mean discomfort from the exoskeleton device. Thus, the opposite of non-fitting or of discomfort would be fit and comfort.
Scope
1.1 This guide covers guidelines and best practices in considering user fit and accommodation of exoskeletons. Accommodation refers to the ability of users to operate and maintain the exoskeleton safely and in the manner for the task(s) for which it was intended, as opposed to the exoskeleton users’ fit to the environment (for example, using an exoskeleton while walking down the aisle of a plane). The manufacturer should specify the anthropometric characteristics of the population for which the exoskeleton was designed so that users may select the appropriate exoskeleton. This would include suggested language for identifying and clearly communicating relevant metrics regarding the fit and adjustment factors for their system, and may clearly specify the population who can use the exoskeleton safely. Appendix X1 provides databases for determining population accommodation and Appendix X2 provides an example of fit for a singular dimension. Lastly, this guide assumes the reader understands the fundamentals behind anthropometry and human biomechanics. The concepts in this guide may be appropriate for medical exoskeletons; however, medical exoskeletons have nuanced use cases which require a lot more specificity. While the guidance here may provide insight to the fit and accommodation of medical exoskeletons, the information herein is not exhaustive and should not replace treatment or oversight from a medical professional.
1.2 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
