Saskia Baltrusch

89 Chapter 4 The purpose of this study was to assess whether wearing a passive trunk exoskeleton affects the metabolic costs of repetitive lifting and walking. In addition, we explored which underlying changes in movement strategy and muscle activation patterns could explain these potential effects. It was hypothesized that wearing an exoskeleton during lifting reduces metabolic costs through a decrease in trunk muscle activity and/ or change in lifting technique. In contrast, it was hypothesized that wearing the exoskeleton during walking increases metabolic costs. Assuming that people normally adopt an optimal step length that minimizes energy cost [23], being forced to adapt step length due to the restriction by the device would likely increase energy costs. 2 Methods 2.1 Passive Exoskeleton In this study, the passive trunk exoskeleton “Laevo” (Intespring, Delft, The Netherlands) was tested (Figure 1). This device is commercially available and in use at different work sites in various companies. It consists of four components: a pad at the anterior side of the chest, leg pads at the anterior side of the thighs, a pelvis belt to keep the device in a fixed position relative to the pelvis, and a smart joint with spring-like characteristics. The chest and thigh components are connected through semi-rigid bars running over this joint, which generates a supporting extension moment at the level of the low back when bending forward. To allow trunk rotation, the chest pad can rotate in the frontal plane of the trunk. Two types of the Laevo, with different angle-moment characteristics, were used for the lifting tasks in this study. According to the manufacturer, the high-cam Laevo predominantly supports the user at bending angles from 0-20 degrees, and the low-cam Laevo predominantly supports the user at bending angles >20 degrees. 4