Metabolic cost adaptations during training with a soft exosuit assisting the hip joint

Fausto A Panizzolo,Conor J Walsh,Michael E Lafiandra,Rebecca A Zifchock,Andrew Long,Nikos Karavas,Gregory M Freisinger,Asa M Eckert-Erdheim,Christopher Siviy

doi:10.1038/s41598-019-45914-5

Abstract

Different adaptation rates have been reported in studies involving ankle exoskeletons designed to reduce the metabolic cost of their wearers. This work aimed to investigate energetic adaptations occurring over multiple training sessions, while walking with a soft exosuit assisting the hip joint. The participants attended five training sessions within 20 days. They walked carrying a load of 20.4 kg for 20 minutes with the exosuit powered and five minutes with the exosuit unpowered. Percentage change in net metabolic cost between the powered and unpowered conditions improved across sessions from −6.2 ± 3.9% (session one) to −10.3 ± 4.7% (session five), indicating a significant effect associated with training. The percentage change at session three (−10.5 ± 4.5%) was similar to the percentage change at session five, indicating that two 20-minute sessions may be sufficient for users to fully adapt and maximize the metabolic benefit provided by the exoskeleton. Retention was also tested measuring the metabolic reduction five months after the last training session. The percent change in metabolic cost during this session (−10.1 ± 3.2%) was similar to the last training session, indicating that the adaptations resulting in reduced metabolic cost are preserved. These outcomes are relevant when evaluating exoskeletons’ performance on naïve users, with a specific focus on hip extension assistance.

Highlights

Lower limb exoskeletons have been proposed as an effective solution for augmenting human walking in individuals with normal gait[1,2,3,4]
This study investigated the adaptations in metabolic cost that occur while walking with a hip assistive device across a relatively high number of sessions
We examined the retention of any metabolic benefits to training, following five months of non-use

Summary

Introduction

Lower limb exoskeletons have been proposed as an effective solution for augmenting human walking in individuals with normal gait[1,2,3,4]. Sawicki and Ferris reported that participants initially had a 7% increase in the metabolic cost of walking on the first day compared to a reduction of 10% on the third day, all in comparison to an unpowered condition They suggest that changes in net metabolic power may occur more slowly than changes in joint kinematics and muscle activation patterns during adaptation to powered walking[7]. This study only included a single testing session, so it is unknown how the metabolic reductions would be impacted with repeated exposure to split-belt treadmill conditions It is unknown how motor adaptation varies when inducing asymmetry with varied belt speeds compared to exoskeletons designed to provide torque as beneficially as possible during gait. Understanding the effects of longer-term training and retention of improved performance are important for the development and the adoption of exoskeletons assisting gait

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Conclusion