Modeling the metabolic reductions of a passive back-support exoskeleton

Abstract

Despite several attempts to quantify the metabolic savings resulting from the use of passive back-support exoskeletons (BSEs), no study has modeled the metabolic change while wearing an exoskeleton during lifting. The objectives of this study were to: 1) quantify the metabolic reductions due to the VT-Lowe's exoskeleton during lifting; and 2) provide a comprehensive model to estimate the metabolic reductions from using a passive BSE. In this study, 15 healthy adults (13M, 2F) of ages 20 to 34 years (mean=25.33, SD=4.43) performed repeated freestyle lifting and lowering of an empty box and a box with 20% of their bodyweight. Oxygen consumption and metabolic expenditure data were collected. A model for metabolic expenditure was developed and fitted with the experimental data of two prior studies and the without-exoskeleton experimental results. The metabolic cost model was then modified to reflect the effect of the exoskeleton. The experimental results revealed that VT-Lowe's exoskeleton significantly lowered the oxygen consumption by ~9% for an empty box and 8% for a 20% bodyweight box, which corresponds to a net metabolic cost reduction of ~12% and ~9%, respectively. The mean metabolic difference (i.e., without-exo minus with-exo) and the 95% confidence interval were 0.36 and (0.2-0.52) [Watts/kg] for 0% bodyweight, and 0.43 and (0.18-0.69) [Watts/kg] for 20% bodyweight. Our modeling predictions for with-exoskeleton conditions were precise, with absolute freestyle prediction errors of <2.1%. The model developed in this study can be modified based on different study designs, and can assist researchers in enhancing designs of future lifting exoskeletons.

The Ethics of Mandatory Exoskeleton Use in Commercial and Industrial Settings

“…If exoskeletons decrease the metabolic energy required to perform repetitive lifting by up to 12% (e.g. as was shown in [84]- [86]), management may assume that workers should be able to utilize that saved energy to work harder or faster, accomplishing more in a given amount of time. However, this logic fails to consider how the work is distributed throughout the worker's body.…”

Evaluation of U.S. Army Soldiers wearing a back exosuit during a field training exercise

“…For instance, studies have repeatedly shown that back exos reduce muscle strain and spinal compression forces, which are risk factors for low back pain and overuse injury (Kermavnar et al, 2020 ; Lamers and Zelik, 2021 ). Back exos have also been observed to reduce muscle fatigue (Lamers et al, 2020 ; dos Anjos et al, 2022 ) and metabolic rate (Baltrusch et al, 2019 ; Alemi et al, 2022 ; Schmalz et al, 2022 ) during bending and lifting tasks, which could enhance endurance or other performance outcomes during physical tasks. Much of the scientific evidence on exos has been generated over the last decade in laboratory experiments or controlled field studies (Kermavnar et al, 2020 ; Crea et al, 2021 ).…”