Saskia Baltrusch

180 Chapter 7 metabolic cost low, and thereby reducing fatigue, might therefore contribute to the prevention of LBP. Two studies have previously assessed the effect of trunk exoskeletons on metabolic cost during lifting, with different outcomes. Whitfield et al. (2014) [19] did not find differences in oxygen consumption when wearing the PLAD exoskeleton. In contrast, a more recent investigation by Baltrusch et al. (2019) [20] found decreased metabolic cost when wearing the Laevo exoskeleton. Both studies attributed their findings on metabolic cost to a change of lifting kinematics when wearing the exoskeleton. Specifically, the PLAD induced users to adopt a squat-like technique when lifting [21], while the Laevo induced a stoop-like technique [20]. It has been shown previously that the squat technique imposes higher metabolic cost than the stoop technique [22]. Neither study investigated the reduction in joint work at the low back and hip that likely occurs due to the external support of the exoskeleton. Previous research has shown that a passive exoskeleton can take over up to 24 % of lumbar moments [14], indicating the potential of an exoskeleton to reduce joint work and by that reducing metabolic cost. Still, such a direct reduction in joint and muscle work has not been investigated yet. Recently, a novel passive exoskeleton (SPEXOR) was designed to reduce peak and cumulative load on the low back [23]. Initial measurements showed that support torques of 20-60Nm can be provided by the exoskeleton, which could substantially reduce muscular effort [23]. Further, pilot testing has revealed little hindrance by the exoskeleton when performing a set of working tasks, which might limit changes in lifting strategy as previously observed with PLAD and Laevo [20]. The aim of this paper is to assess the effect of wearing the SPEXOR exoskeleton on metabolic cost. In addition, to explain potential differences in metabolic cost, we assessed the effect of the exoskeleton on kinematics, and muscle activity. 2 Methods 2.1 Passive Exoskeleton In this study, we tested the passive spinal exoskeleton SPEXOR that was designed and built to reduce peak and cumulative load on the low back [23]. It consists