Saskia Baltrusch

105 Chapter 4 Since lifting requires trunk inclination of more than 20 degrees, we expected a bigger effect of the low-cam exoskeleton, which is supposed to support the user at bending angles >20 degrees, compared to the high-cam exoskeleton, which is supposed to support the user at bending angles from 0-20 degrees. However, the low-cam exoskeleton showed smaller and non-significant effects on metabolic costs. We therefore assessed the torque-angle characteristic of the device in a “post-hoc” measurement, to test whether it matches the description of the manufacturer. By using a force transducer, we measured chest pad forces when a participant was performing trunk bending motions through the full range of motion of the exoskeleton. Additionally, we assessed the angle of the exoskeleton hip joint, using Optotrak motion capture markers [29]. The results of this measurement are shown in figure 10. Figure 10: The angle-torque relationship of the high- and low-cam exoskeleton. The vertical black lines represent the operating range of the device during lifting from knee height (dashed line) and ankle height (solid line)(adapted from Koopman et al., 2019 [29]). The maximal support of the high-cam device is reached at a Laevo angle of about 35 degrees. This is within the range of joint angle that was reached during lifting. This in contrast to the low-cam exoskeleton, that provides a maximal support at a joint angle>100 degrees, which was never reached by the participants during lifting. The steep incline of the torque in the end range of motion of both types 4