Will They Make the Workplace Safer?
Evaluating Exoskeletons

According to a study published by Markets and Markets, the exoskeleton market is expected to grow to $2.8 billion by 2023. Much is still unknown about this emerging technology’s ability to improve worker performance and workplace safety. If industrial hygienists have not already confronted questions about exoskeletons and their use across industry, they will need to do so shortly. Often, these questions center around the need to identify and evaluate the unique characteristics of exoskeletons to understand any unintended consequences associated with their use. The goal of this article is to help industrial hygienists and other health and safety professionals understand the differences between exoskeleton types and how to effectively evaluate and determine whether exoskeletons are a viable solution for their organization.

WHAT IS AN EXOSKELETON? A December 2019 commentary published in the American Journal of Industrial Medicine describes an exoskeleton as a wearable device or structure that “augments, enables, assists, and/or enhances physical activity through mechanical interaction with the body.” There are two major types of industrial exoskeletons: active and passive. 
Active exoskeletons use a system of motors, pneumatics, hydraulics, or a combination of technologies to enhance the worker’s power. They are typically used by those who have permanent physical disabilities; for example, they can allow paralyzed persons to walk and those with limited upper extremity function to use these limbs with dexterity. Since active exoskeletons are typically used for non-sedentary tasks and by those with permanent physical disabilities, they are not currently good candidates for workplace use. Their limitations include battery life, complexity, and cost. In the future, however, active exoskeletons may play a role in some return-to-work cases.
This article focuses on passive exoskeletons, as they are more often used in occupational settings. As explained in a 2015 paper in the journal Ergonomics, a passive exoskeleton uses energy from human motion stored in springs or other materials to support a movement or posture. The American Journal of Industrial Medicine commentary mentioned previously refers to three common groups of passive exoskeletons currently
in use:
  • Back-assist exoskeletons support the lumbar spine while lifting or holding a load.
  • Shoulder- and arm-assist exoskeletons support the arms and shoulders during sustained overhead work. These can also provide an extra “arm” to hold a tool for a prolonged period.
  • Leg-assist exoskeletons support the ankle, knee, or hip joints while carrying a load. They may also take the place of an ordinary chair.
EVALUATING EXOSKELETONS FOR OCCUPATIONAL USE As exoskeleton technology is still emerging, it can be difficult for IHs to choose a product that’s right for their organizations. Methodologies for measuring exoskeleton performance can differ from manufacturer to manufacturer. While manufacturers will often outline the benefits of their products’ use in manuals and other product literature, highlighting force reduction or elimination, the lack of standardization can make it challenging for IHs to truly understand the benefits of using the devices. Failure to accurately evaluate the product could lead to results that fail to meet expectations and may underestimate the transfer of force to unintended body parts, including the joints and spine.
THE HIERARCHY OF CONTROLS The first step in evaluating the organization’s potential need for exoskeletons is to review the hierarchy of controls (Figure 1). Passive exoskeletons are often marketed as engineering controls. However, use of an exoskeleton does not isolate workers from the hazard; in fact, the hazard still exists. An exoskeleton thus would be incorrectly categorized as an engineering control because the task is not altered; rather equipment is added to the individual. By definition, the exoskeleton falls into the lower categories of administrative controls or personal protective equipment (PPE) on the hierarchy pyramid.
Before seeking out an exoskeleton product, an IH’s priority should be to determine whether a better solution can be achieved through eliminating the hazard or the task requiring it, substituting the hazardous task with one that is safer, or applying engineering controls to prevent workers from being put at risk during the task.
Exoskeletons should only be considered after thorough assessments are completed and other controls are not considered viable.
Figure 1. The hierarchy of controls.
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UNDERSTANDING EXOSKELETON INTERACTIONS IN THE OCCUPATIONAL SETTING According to Maury Nussbaum, PhD, CPE, FAIHA, a professor in the Department of Industrial and Systems Engineering at Virginia Tech, the decision to deploy exoskeletons in an organization involves recognizing a complex interaction between the task, the worker, and the exoskeleton. This interaction could reduce the worker’s physical demands and injury risk, as well as potentially enhance task performance. However, Nussbaum cautions that very little is known about the long-term interactions between an exoskeleton and an individual worker. Technology changes quickly, Nussbaum says, and it is difficult for research to keep up with “new and improved” devices.
Understanding the interactions between a task’s physical requirements, the worker’s expectations and limitations regarding the task, and the exoskeleton’s capabilities can help not only with selecting an effective device, but also with identifying potential new hazards that may result from its introduction.
Choosing an exoskeleton involves determining which product is most suitable for the task and the extent of its integration into the workplace. As explained in a February 2020 paper published in the journal Applied Sciences, selection of an exoskeleton raises the following questions and concerns:
Defining the task’s physical requirements:
  • Is the task physically demanding? Does the exoskeleton under consideration provide support to the back for lifting tasks or the shoulders for overhead or reaching tasks?
  • If the task involves twisting (non-sagittal plane) or lifting, does the exoskeleton create the potential for additional twisting stress? If so, this will likely increase the workload on the musculoskeletal system.
  • Does the task require additional PPE or other items such as tool belts? These may interfere with the exoskeleton fit and working postures.
Defining the worker’s expectations to perform the task:
  • Does the exoskeleton provide an appropriate fit for the worker demographics? Exoskeletons have limited adjustability and may not be comfortable for use by all workers.
  • Will workers share exoskeletons? If so, then hygiene, cleanliness, and the possible presence of chemicals are concerns.
  • What supplies are required to clean the exoskeleton, and how long will cleaning take?
  • How will exoskeletons be securely and properly stored?
  • How long does it take to don or doff the exoskeleton? Some exoskeletons may require additional time and effort or even require another worker to assist the wearer in adjusting it properly or removing it.
  • Does the exoskeleton come with any replaceable features, such as load springs, that make the unit customizable for the worker? If so, this will require additional worker testing and training, and reminders for workers to use their individual support settings.
Defining the exoskeleton’s capabilities:
  • What are the exoskeleton’s technical features, such as weight and size?
  • What are its storage requirements?
  • Is the exoskeleton expected to provide an ergonomic benefit?
  • Does wearing the exoskeleton affect the time it takes for the worker to perform the task?
UNDERSTANDING EXOSKELETON MANUFACTURER DATA The next step after evaluating the interaction between the task, the worker, and the exoskeleton is to review the manufacturer’s information on the exoskeleton, which helps determine whether the device will provide its promised return on investment. It is important to understand the manufacturer’s performance claims and how they were derived. When a worker uses an exoskeleton, the force required to perform the task does not suddenly disappear; it is simply redirected to another area of the body. When reviewing manufacturer findings on device performance, it is important to understand these tradeoffs.
According to William Marras, PhD, CPE, professor of neurological surgery and executive director of the Spine Research Institute at Ohio State University, two commonly used measurement tools in exoskeleton product literature are employee perception and surface electromyography (EMG) studies. 
Exoskeletons should only be considered after thorough assessments are completed and other controls are not considered viable.
Perception surveys are easy, cost-effective tools to measure user comfort before and after the exoskeleton’s implementation. While survey data is relatively instantaneous and easy to interpret, users’ perception surveys do not measure the transfer of force. Rather, they may show short-term positive impacts before users experience cumulative musculoskeletal effects. The perception survey results may also be misleading since users may not be aware that exoskeletons are transferring force to other body parts where localized nerve endings are not as prevalent. In addition, the body parts where force is transferred (such as discs) are not measured by the survey. Further, an employee who previously advocated for exoskeletons in the workplace will likely report positive effects, even if the unit does not respond or assist as expected. To counter this bias, perception surveys should be repeated six months and one year after the exoskeleton is introduced. IHs should check the literature for additional data sources to improve their evaluations, such as rates of worker injuries before and after product introduction, comparisons of time spent by workers in awkward postures with and without the product, and EMG readings.
Surface EMG is a measurement technique in which electrodes are placed on the skin overlaying a muscle to detect electrical activity (muscle activation). But studies using EMGs may be misleading if the data is not normalized or modulated for muscle length and velocity, which can influence the relationship between electrical and mechanical activity of that muscle. In addition, even if the EMG produces a value relative to the volume of motor units active, the force that muscles generate depends on other factors such as muscle fiber length, gain, and velocity. Each of these variables could affect interpretation of the EMG results; for example, they could indicate lower activation when muscles are stretched. A 2018 Applied Ergonomics paper suggested that for these reasons, EMG results must be evaluated with caution, especially regarding tests in which subjects perform a variety of tasks or activities.
When EMG data is included in manufacturer-provided guidance, IHs should also know that results are affected by the body location where the electrodes were placed during data collection. For example, measuring EMG in the shoulder region may show a reduction in stress, but the force will transfer to another part of the body or another part of the same muscle where the electrode cannot detect it. Therefore, evaluating local impacts may suggest the exoskeleton is effective. However, only when looking at the connected structures of the musculoskeletal system will negative effects due to force transfer be found.
Measurement systems that use 3D muscle modeling are most accurate as they account for muscle volume when displaying muscle activation and effectively expand the areas of observation. These measurement systems measure the forces imposed on the spine that could cause damage when the worker cannot perceive it. As explained in the Applied Ergonomics paper, spinal force is cumulative, and its effects will not necessarily be perceived or felt until after an injury occurs.
AN EMERGING TECHNOLOGY When considering use of a passive exoskeleton, the following concepts can allow better understanding of a device’s limitations and help with selection of the right exoskeleton for a trial. 
Most passive exoskeletons are designed to work within the sagittal plane; that is, they are designed for tasks that do not require twisting. Work that is dynamic or that requires movements from the sagittal plane will likely result in the user “fighting” the device, thereby transferring force to opposing joints.
Assumptions made using static models such as EMG may only capture muscle activation with the targeted one or two muscles engaged. As a result, increased muscle activation in supporting or surrounding muscles during the work activity will be missed and tissue load will be underestimated. Most research examines only biomechanical force reductions in the static position and not for dynamic postures.
Finally, few exoskeletons on the market have been certified to comply with emerging international safety standards. This is mostly due to the infancy of exoskeleton standard development and the fact that most models on the market haven’t been evaluated.
ELLEN GALLO, CSP, CPE, MSC, is a senior risk consultant with Aon Global Risk Consulting.
ROBERT BAFT, CIH, CPE, CSP, is the corporate industrial hygienist with FedEx Ground.
ALBERT MOORE, MS, CIH, CPE, is a PhD student with Industrial & Systems Engineering at Virginia Tech.
BOB DEIST, CIH, CIT, is the senior vice president at Chartwell Staffing Services.
Authors’ note: Maury A. Nussbaum, PhD, CPE, FAIHA, and William S. Marras, PhD, CPE, were consulted for this article.

Editor's note: The version of this article printed in the January 2021 issue mistakenly asserts that the ISO 31000 standard includes estimates of the percentage reduction in hazard risk provided by administrative controls and by PPE, respectively. These estimates do not appear in ISO 31000. The incorrect sentences were removed from the digital version of the article on Jan. 13, 2021.
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American Journal of Industrial Medicine: “Industrial Exoskeletons: Need for Intervention Effectiveness Research” (December 2019).
ANSI/ASSP/ISO 31000, Risk Management Standards (2018).
Applied Ergonomics: “Biomechanical Evaluation of Exoskeleton Use on Loading of the Lumbar Spine” (April 2018).
Applied Sciences: “Methodology of Employing Exoskeleton Technology in Manufacturing by Considering Time-Related and Ergonomics Influences” (February 2020).
Ergonomics: “Exoskeletons for Industrial Application and their Potential Effects on Physical Workload” (February 2019).
Markets and Markets: “Exoskeleton Market by Component, Type, Mobility, Body Part, Vertical, and Geography” (November 2017).