Wearable Exoskeletons to Reduce Physical Load at Work

Robotic-like suits which provide powered assist and increase human strength may conjure thoughts of sci-fi and superhero film genres. But these wearable exoskeleton devices are now a reality and the market for their applications in the workplace is projected to increase significantly in the next five years.  As with any technologic innovation some of the pros and cons and barriers to adoption are not completely understood.  In this blog our objectives are to:  (1) describe wearable exoskeletons in the context of workplace safety and health control strategies; (2) highlight current and projected trends related to industrial applications of these technologies; and (3) invite input from our stakeholders on workplace health and safety experiences, positive or negative, with these devices.

The wearable exoskeleton was defined by de Looze et al. (2015) as “…a wearable, external mechanical structure that enhances the power of a person. Exoskeletons can be classified as ‘active’ or ‘passive’. An active exoskeleton comprises one or more actuators that augments the human’s power and helps in actuating the human joints. …A strictly passive system does not use any type of actuator, but rather uses materials, springs or dampers with the ability to store energy harvested by human motion and to use this as required to support a posture or a motion.” Passive systems require no external power and use springs, elastic cords, or other resilient elements to provide either a restoring moment that unloads the low back muscles, or additional vertical lift force to augment arm and shoulder muscles when supporting tools or materials. More complex active exoskeleton systems use electric servo-motors and powered actuators on an external frame with joints matched to those of the worker. The actuators augment the joint torque of the wearer so he or she can handle external loads with less effort than in their unassisted capability. These devices are often portrayed as modern or futuristic technology; however, they have a long history as a rehabilitation/assistive technology. A U.S. patent (see sketch below) was awarded in 1890 for an “Apparatus for facilitating walking” (Yagn, 1890 US Patent).

From the standpoint of workplace health and safety, wearable exoskeleton devices may be beneficial in reducing musculoskeletal loads that are not otherwise abated by engineering process change.  Lifting and handling of heavy materials and supporting heavy tools are contributors to fatigue and musculoskeletal disorders (MSDs) which are known to account for approximately 30% of lost time workplace injuries and illnesses. Liberty Mutual Insurance Company estimated the direct costs of injuries due to overexertion involving an outside source (from lifting, pushing, pulling, turning, throwing, or catching) to be $15.1 billion in 2012 – representing one quarter of the total workplace injury direct costs (Liberty Mutual, 2014).

The preferred approach to reducing exposure to musculoskeletal injury risk factors follows the hierarchy of controls in which the work would be redesigned to mitigate the risk through engineering controls or process change. Examples include reducing weights of tools or materials, or changing the layout of the work area to avoid body postures and manual forces that put workers at risk when handling heavy tools or materials.  Recognizing that this is not always feasible, a less preferred approach is to provide equipment worn by the employee as personal protection.  Wearable passive corsets, in the form of back belts or lifting belts, have been commercially available for years as a form of personal equipment purported to reduce back injury risk during lifting.   A NIOSH review of back belt studies in the 1990s (“Workplace Use of Back Belts. Review and Recommendations”) found insufficient evidence of their effectiveness in preventing injury to classify back belts as an effective form of PPE. In its 1994 summary NIOSH recommended that, in lieu of the back belt, “…The most effective way to prevent back injury is to redesign the work environment and work tasks to reduce the hazards of lifting.” That recommendation, addressing the effectiveness of a control strategy involving a wearable device, is similarly applicable to the wearable exoskeleton of today.

Regardless of their place on the control hierarchy, the market for industrial use of wearable exoskeletons is projected to increase. According to a recent market research report (WinterGreen, Research Inc., 2015)[1] in 2016 the medical/rehabilitation applications will likely comprise 97% of the total market for wearable exoskeletons compared with only 3% for work-related/industrial applications.  This report projects that within five years the industrial market share will equal that of the medical/rehabilitation. Market forecasts from this report suggest growth in the industrial market from $2.9 million in 2016 to $1.12 billion in 2021 – an average growth of 229% per year. Use in the Shipbuilding industry, now underway, represents a high market percentage initially, but greater increases in market share are projected in the Construction, Warehousing, and Manufacturing industries.

NIOSH has not reviewed evidence related to wearable exoskeletons in the prevention of workplace musculoskeletal injuries and illnesses.  However, a recent literature review by de Looze et al. (2015) identified 40 scientific studies conducted in 1995-2014 that examined the effect of exoskeletons on reducing musculoskeletal loading.  The majority of these studies evaluated these effects in a laboratory setting and several studies did report decreased back muscle activity and compressive forces in the lower spine.  Because most of the studies have been in laboratory environments, more information on worker acceptance and adoption of the devices and long-term use in real work environments is needed.

A number of active Department of Defense research programs are exploring the extent to which exoskeleton technologies can augment physical capabilities in military applications. An example is the DARPA (Defense Advanced Research Projects Agency) Warrior Web program in which injury mitigation technologies are an objective in research and development. Systems are being evaluated by the Naval Surface Warfare Center and the Natick Soldier Research, Development and Engineering Center.  These groups have identified safety-based criteria for exoskeleton systems and are beginning to study longer term effects of their use.  Additionally, a European consortium, called the “Robo-Mate” project, comprising 12 partners from seven European countries, has been formally established to evaluate current regulations relating to exoskeletons and to outline potential risks to workers using exoskeletons in manual handling activities in industrial settings.  The partners include end-users from automotive and dismantling industries, industrial robotics/technology developers, a robotics integrator, and ergonomics research groups.

Several exoskeleton developers have recently approached NIOSH program managers with demonstrations of exoskeleton technology transfer. These devices appear to have benefits in some specific industry applications for reducing injury risk factors.  As their prices decrease we may anticipate more workplace interest in exoskeleton technologies.  However, their occupational use should be evaluated for their potential benefits and potential competing risks before widespread workplace adoption.  Some questions to address include, but are not limited to:

• Do some devices create a transference of load between musculoskeletal regions that still puts the worker at risk? For example, a vest or hip-supported device may transfer load off the arms and shoulders, but the increase in total load transferred to the spine and lower extremities may also have long term effects.
• Does the added weight of some devices increase energy expenditure/metabolic work load? Do some devices affect user comfort?
• Do some devices affect the balance of the wearer by changing their center of mass or increasing rate of fatigue in the lower extremity muscles? As reported by de Looze et al. (2015) increases in leg muscle activity have been reported for some devices (e.g. Barret and Fathallah, 2001; Ulrey and Fathallah, 2013); this may occur because the “external forces applied by the [exoskeleton] equipment needs to be counteracted to retain balance…”. Can this increase in leg muscle activity contribute to lower extremity fatigue and increased risk for loss of balance? Correspondingly, are fall risks increased because of this possible leg fatigue and loss of balance?
• Do some devices affect patterns of muscle use or change normal joint mechanics, putting workers at risk while using the device, or when not wearing the device in their non-work activities? For example, are there effects on a worker using a passive exoskeleton device all day who becomes accustomed to continual external assistance provided to his/her back muscles?
• Do these devices create a potential “false sense of security” for handling heavy loads? This was a concern raised in regard to back belt use. Might it also be applicable to the use of exoskeletons?
• If exoskeletons are proven effective, how do we establish workplace practices that appropriately increase acceptable lifting/handling weight limits while maintaining safe physical loads for the worker’s augmented capacity?

Input/Collaboration

The authors and the NIOSH Musculoskeletal Health Cross Sector program are interested in industry stakeholder experiences, positive or negative, with wearable exoskeleton devices to reduce physical load and prevent injury to workers.  In what industries and specific occupations have these devices been successful and in what industries/occupations have they not?  Industry experience can reveal issues and barriers to worker acceptance that are not evident in a controlled laboratory environment.   We invite you to share relevant experiences with wearable exoskeleton technologies by commenting below.

If you are using exoskeletons in your workplace and would be interested in collaborating with NIOSH on evaluation, please contact us at: nioshmsdprogram@cdc.gov.

Brian D. Lowe, PhD, CPE; Robert B. Dick, PhD, Captain USPHS (Ret.); Stephen Hudock, PhD, CSP; and Thomas Bobick, PhD, CSP, CPE

Dr. Lowe is a Research Industrial Engineer in the  NIOSH Division of Applied Research and Technology.

CAPT Dick is a visiting scientist in the NIOSH Division of Applied Research and Technology.

Dr. Hudock is a Lead Research Safety Engineer in the NIOSH  Division of Applied Research and Technology.

Dr. Bobick is a Research Safety Engineer in the NIOSH Division of Safety Research.

References to products or services do not constitute an endorsement by NIOSH or the U.S. government.

References

Barret, A.L. and F.A. Fathallah (2001). Evaluation of Four Weight Transfer Devices for Reducing Loads on the Lower Back during Agricultural Stoop Labor, Paper Number, 01-8056 of the American Society of Agricultural Engineers Meeting, Sacramento, USA

de Looze, MP, Bosch, T, Krause, F, Stadler, KS and O’Sullivan, LW (2015). Exoskeletons for industrial application and their potential effects on physical work load, Ergonomics, DOI: 10.1080/00140139.2015.1081988

Liberty Mutual Insurance Company (2014). Workplace Safety Index 2012.

NIOSH (1994). Workplace Use of Back Belts.  Review and Recommendations. Publication number 1994-122.

NIOSH (1994). Back belts.  Do they Prevent Injury?  Publication number 1994-127.

Ulrey, B.L. and F.A. Fathallah (2013). Subject-specific Whole-body Models of the Stooped Posture with a Personal Weight Transfer Device, Journal of Electromyography and Kinesiology 23(1): 206-215.

van der Vorm, J, Nugent, R, O’Sullivan, L. (2015). Safety and Risk Management in designing for the lifecycle of an exoskeleton:  A novel process developed in the Robo-Mate project.  Procedia Manufacturing, 3:1410-1417.

WinterGreen Research, Inc. (2015).  Wearable Robots, Exoskeletons: Market Shares, Market Strategies, and Market Forecasts, 2015 to 2021.  REPORT # SH26511914, Lexington, Massachusetts:  WinterGreen Research, Inc.

Yagn, N. (1890). Apparatus for facilitating walking. US Patent No. 440684A.

[1] These are market projection data from a non-peer reviewed report.