What is the current state of evidence on passive exoskeletons designed to support the lumbar region? A systematic review and meta-analysis of physiological, biomechanical, and user-related outcomes.

INTRODUCTION: Work-related musculoskeletal disorders (WMSDs) are the most commonly reported health problem among workers in Europe. Manual handling of loads and awkward postures are cited as important risk factors for WMSDs. Exoskeletons, wearable devices that support and stabilize the locomotor system, are emerging as a lifting aid that could reduce muscular effort and potentially lessen the impact and the prevalence of WMSDs among manual workers. This systematic review and meta-analysis aims to summarize the current scientific evidence on passive exoskeletons designed to support the lower back. METHODS: A systematic search was conducted on Pubmed, Scopus, EMBASE, Web of Science and CINAHL, including papers investigating the acute effects of passive lumbar exoskeletons and studies comparing experimental and control groups. A three-level meta-analysis was conducted for five groups of outcomes: electromyographic evaluations, subjective reports of effort and discomfort, kinetic and metabolic measurements and performance in functional tests. RESULTS: We retrieved 1750 items, and ultimately included 50 articles, encompassing a total of 787 participants. The pooled effect sizes (with 95% Confidence Intervals and p value) for each outcome were: EMG = 0.29 (0.19; 0.40, p < .0001); subjective outcomes = 0.10 (-0.09; 0.30, p = .30); kinetic outcomes = 0.47 (0.24; 0.70, p < .0001); metabolic outcomes = 0.15 (0.08; 0.23, p < .0001); performance = -0.10 (-0.27; 0.06, p = .22). Body part was a significant moderator for EMG, while task domain was a moderator for subjective reports. DISCUSSION: Passive back-support exoskeletons have a positive effect on muscular activation, as well as kinetic and metabolic outcomes. However, the effect on subjective perceptions and performance appears non-significant due to the coexistence of positive and negative effects on different tasks and body parts. All of the included studies adopted a within-subject design, and most were of moderate methodological quality. CONCLUSION: This type of exoskeletons shows a modest yet significant biomechanical and physiological effect, which is attributable to reduced muscle activity and spinal loading. Further longitudinal studies are needed to assess the long-term effects of these adaptations.