Saskia Baltrusch

108 Chapter 4 to avoid fatigue [32]. According to Wu and Wang (2002) [10] employees should not exceed 34% of their aerobic capacity when working shifts of 8 hours. This is in line with other research [32-35], which recommends that the level of oxygen consumption should not exceed 33% of O 2 max for working in shifts that last between 2 and 8 hours. To understand the relevance of our results we can express our observed effects in similar terms of relative aerobic load. Assuming that our participants walked at 36% of their aerobic capacity in our self-selected walking speed trials (conform the finding of Astrand et al., 2003 [32]) we can estimate that lifting from knee and ankle height without the exoskeleton required ~36% and ~51%, respectively. Wearing the high-cam exoskeleton reduced these values to ~33% and ~47% oxygen consumption. Although the reduction in relative load by 3-4% appears small, it may be relevant for the working population, considering that aerobic load of repetitive lifting in this study is around or exceeding the recommended maximal aerobic load indicated in literature. Thus, reducing the net metabolic consumption with the use of an exoskeleton is a relevant possibility to enhance safe work without undue fatigue. Certainly, future studies are needed to prove this statement. Our findings suggest that exoskeletons are of benefit for lifting by decreasing physiological strain. Work-related low-back pain, in particular, might be preventable when wearing an exoskeleton, due to a lower risk of getting fatigued. Data on underlying changes in muscle activity and movement strategies provided insights for further optimization of exoskeleton design from the perspective of metabolic costs. Future studies are needed to corroborate underlying mechanisms and design optimizations.