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OCCUPATIONAL APPLICATIONS
Military personnel are at greater risk of injuries due to frequent load carriage. Novel exoskeleton technology may have benefits for soldiers, such as reduced physical burden through load carriage support that may result in decreased metabolic cost, reduced fatigue, and lower risk of injuries during walking. However, as for most assistive devices, a familiarization period is likely necessary to obtain the full potential of the device. Our results show that the metabolic cost of walking (MWC) was initially increased significantly upon provision of the passive exoskeleton, though it returned to baseline values after a 9-day familiarization period. The exoskeleton remained effective after a three-month pause, with a MCW below baseline. These results suggest that to properly assess the assistance of an exoskeleton, a sufficient familiarization period should be mandatory.
TECHNICAL ABSTRACT
Background: Military load carriage has been shown to alter gait patterns, resulting in an increased metabolic cost during walking (MCW). Soldiers’ burden could be mitigated by wearing a passive exoskeleton, but the additional payload of the device can alter movement patterns during gait, rendering it detrimental. Integrating principles of motor learning during a familiarization period could allow users to develop adaptive motor strategies, thereby decreasing MCW.
Purpose: The aim of this study was to explore the influence of a familiarization period on MCW when soldiers wear a passive, load-bearing, prototype exoskeleton (Exo).
Methods: Three male soldiers walked on a treadmill with a 38 kg payload at eight speeds (1.8-6.0 km/h) under five conditions: 1) no exoskeleton (NoExo); 2) exoskeleton pre-familiarization (ExoPre); 3) exoskeleton post-familiarization (ExoPost); 4) no exoskeleton follow-up (NoExoFU); and 5) exoskeleton follow-up (ExoFU). Each experimental trial consisted of 10 minutes of standing followed by 10 minutes of walking at a constant speed. Metabolic data were normalized to walking speed (J/kg·m) to obtain the MCW. The familiarization period consisted of 9 days of activities with the exoskeleton using a standardized protocol. Differences in MCW with and without the Exo were compared at the eight walking speeds using a nonparametric analysis of Longitudinal Data.
Results: There was a statistically significant decrease in MCW after familiarization with the Exo, particularly during ExoFU with a relative treatment effect of 0.11 − 0.19. There were also significant reductions in MCW during ExoFU when compared to NoExoFU [participant 01 = 0.37; participant 02 = 0.27; participant 03 = 0.35].
Conclusions: A first exposure to the exoskeleton increased MCW. After familiarization, however, the MCW with the Exo returned to the NoExo level or below with a payload of 38 kg among three soldiers. A familiarization period of 3 hours per day over 2 weeks of familiarization may optimize the use of an exoskeleton.
Acknowledgments
The authors would like to thank Ms Jenna Crocker for her implication during data collection.
Conflict of Interest
Two authors of this work are employees of the manufacturer of the exoskeleton used in this study but did not receive any benefit from being associated with this research.