Saskia Baltrusch

97 Chapter 4 Figure 4: Range of motion in the knee joint (a), hip joint (b), LS51 joint (c) and trunk (d) when lifting from knee and ankle height ,averaged over all particpants. N=11. Error bars indicate standard deviations. The average range of motion of the centre of mass (COM) did not show a significant difference between the exoskeleton conditions when lifting from knee height. However, in line with joint ROM, when lifting from ankle height, the range of motion of the COM tended to be lower when wearing the exoskeleton, compared to control condition (Figure 5a). This approached significance (p=0.056). Figures 5b and 5c show the lowest and highest position of the COM, averaged over participants. Again, no significant differences between the exoskeleton conditions were found, but the figure demonstrates that the potential difference in range of motion of the COM mostly resulted from a decrease in downward movement when wearing the exoskeleton and not from a lack of extending upwards. Muscle activity The muscle activity of the trunk muscles over a lifting cycle is shown in Figures 6a (lifting from knee height) and 6b (lifting from ankle height). Although on average peak muscle activity of the back muscles seemed to be lower when wearing the exoskeleton, especially when lifting from ankle height, this difference was not significant in any period of the lifting cycle. In contrast, abdominal muscles did show significant main effects of exoskeleton for both lifting heights. The muscle activity of m. rectus abdominus showed a small but significant increase when 4