Abstract
BackgroundThe purpose of augmentative exoskeletons is to help people exceed the limitations of their human bodies, but this cannot be realized unless people choose to use these exciting technologies. Although human walking efficiency has been highly optimized over generations, exoskeletons have been able to consistently improve this efficiency by 10–15%. However, despite these measurable improvements, exoskeletons today remain confined to the laboratory. To achieve widespread adoption, exoskeletons must not only exceed the efficiency of human walking, but also provide a perceivable benefit to their wearers.MethodsIn this study, we quantify the perceptual threshold of the metabolic efficiency benefit provided during exoskeleton-assisted locomotion. Ten participants wore bilateral ankle exoskeletons during continuous walking. The assistance provided by the exoskeletons was varied in 2 min intervals while participants provided feedback on their metabolic rate. These data were aggregated and used to estimate the perceptual threshold.ResultsParticipants were able to detect a change in their metabolic rate of 22.7% (SD: 17.0%) with 75% accuracy. This indicates that in the short term and on average, wearers cannot yet reliably perceive the metabolic benefits of today’s augmentative exoskeletons.ConclusionsIf wearers cannot perceive the benefits provided by these technologies, it will negatively affect their impact, including long-term adoption and product viability. Future exoskeleton researchers and designers can use these methods and results to inform the development of exoskeletons that reach their potential.
Highlights
The purpose of augmentative exoskeletons is to help people exceed the limitations of their human bodies, but this cannot be realized unless people choose to use these exciting technologies
Differences in the Just Noticeable Difference (JND) can be observed by comparing the shapes of these distributions; for example, a narrow distribution with a defined peak at a low value represents a participant who is highly attuned to changes in energetics, while a flattened distribution with a peak at a high value denotes a participant with a greater JND and less sensitivity
We examined the range of absolute metabolic rates experienced by participants in our protocol and verified that the metabolic rates humans experience while walking with an assistive exoskeleton were included in this range (∼ 10% reductions from unassisted walking, see Fig. 3E)
Summary
The purpose of augmentative exoskeletons is to help people exceed the limitations of their human bodies, but this cannot be realized unless people choose to use these exciting technologies. The purpose of augmentative exoskeletons is to help people exceed the limitations of their human bodies These technologies apply mechanical assistance to the joints of the legs during locomotion, thereby reducing the physical demands on the wearer’s neuromuscular system. Medrano et al Journal of NeuroEngineering and Rehabilitation (2022) 19:26 expenditure needed for walking by approximately 14% relative to not wearing an exoskeleton [2, 5, 9,10,11,12,13,14] These exoskeletons apply powered assistance at either the ankle joint [5, 9,10,11,12,13,14] or hip joint [2] and implement control strategies that operate in tandem with the wearer to reduce their metabolic expenditure. Metabolic expenditure can be objectively measured in a laboratory setting, meaning it does not have the challenge of quantification that plagues other potentially subjective metrics of success (e.g. comfort, stability, or preference, among others)
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