###### Abstract  
Soft back exoskeletons are aimed at reducing musculoskeletal effort during manual handling tasks, contributing to the prevention of low back disorders like lumbar strains and sprains or intervertebral disk problems. However, large differences in their biomechanical effects are observed in the literature. A possible explanation could be the lack or disparity of familiarization protocols with the exoskeleton. The aim of this experimental study was to characterize the familiarization process with a soft back-support occupational exoskeleton and determine the time needed to stabilize biomechanical variables. Participants carried out 6 familiarization sessions of \(1\,\mathrm{h}\) to the CORFOR(r) soft back-exoskeleton. Joint kinematics, postural stability, exoskeleton pressure perception, muscle activity, and performance were measured at the beginning of the first session and at the end of each session during stoop and squat liftings. Results showed that back kinematics, performance, and exoskeleton pressure perception changed during the first sessions and stabilized after sessions 3 or 4, depending on the variable. The authors recommend a familiarization protocol for the CORFOR(r) soft back-exoskeleton of 4 sessions of 1 h duration. This recommendation could help CORFOR(r) users, for instance, in the automotive industry, the food retail industry, or the agriculture field. motor control; motion analysis; motor learning; exoskeleton; biomechanics +
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a task, during which motor learning is needed to reach the same motor behavior as prior to the new parameter's exposure [15]. Accordingly, measuring the motor behavior during the early stage of exoskeleton use might lead to non-representative motor behavior during long-term exoskeleton use. Put differently, if familiarization with the exoskeleton is not achieved, the assessment of its potential benefits can be misestimated. This might also be the source of the divergent results within the literature because of varying familiarization periods. Some authors worked on the familiarization process with walking exoskeletons [13; 14; 16]. For instance, [PERSON] et al. (2022) [16] recently observed that a 9-day familiarization period with the use of a multi-joint exoskeleton by soldiers led to a diminution of the metabolic cost during walking. However, these authors did not characterize the evolution of this variable during the familiarization protocol. Contrariwise, [PERSON] et al. (2013) [14] showed a decrease in metabolic cost during the first 18.5 min of walking with an ankle exoskeleton, followed by a stabilization. Moreover, [PERSON] et al. (2019) [13] studied a longer familiarization process based on five sessions lasting 20 min. These authors showed a diminution of the metabolic cost when walking with a hip exoskeleton until the third session, followed by a stabilization. Despite the discrepancy in exoskeleton types, this familiarization model assessed on walking exoskeletons may be transferred to passive occupational back exoskeletons. However, among the 51 papers cited in three literature reviews about exoskeletons [3; 6; 17], 25 articles did not mention any familiarization process before measurements. In the remaining 26 studies, only nine described the task and duration used for the familiarization. Among these studies, different familiarization durations were used, ranging from 10 min [18] to 4 sessions of 97 min duration [11], but none of them actually verified the stabilization of the motor behavior, possibly leading to non-representative data about the effects of the exoskeleton use. In addition, changes and steady states of biomechanical metrics during familiarization are currently unknown. But these parameters, such as trunk or back muscle activity, back, hip, and knee kinematics [9; 19], movement's execution [20], or postural stability [11], would certainly be relevant to point out the influence of an exoskeleton's use and be representative of the familiarization process.