Saskia Baltrusch

87 Chapter 4 1 Introduction Most adults (60-80%) experience low-back pain (LBP) at some point in their lifetime [1]. Many suffer from relapses of pain (44-78%) and work absence (26- 37%) [2]. The financial and economic burden of back pain, due to direct costs and work absence, is substantial [3,4]. Cost-effective interventions, focusing on prevention of LBP and return-to-work management, are essential to decrease its incidence and its burden on society. There is strong epidemiological evidence that physical demands of work, such as manual materials handling and lifting, are associated with increased reports of back symptoms [5-7]. Therefore, researchers and clinicians have focused on reducing work-related risk factors for LBP by implementing interventions to decrease mechanical low-back load at work. According to the guidelines of the National Institute for Occupational Safety and Health (NIOSH), besides the mechanical load, physiological strain needs to be taken into account to guarantee safe manual material handling. High physiological strain can result in systemic or local fatigue [8] leading to an increased risk of lifting-related LBP. Janssens et al. (2010) [9] found that systemic fatigue causes impaired coordination, potentially leading to an increased risk of low back injury. Furthermore, Wu and Wang (2002) [10] have shown that there is a negative relationship between maximum acceptable work time and physical workload, measured in terms of aerobic strain. They recommend an upper limit of 34% O 2 max (maximum rate of oxygen consumption (l/kg/min)) for dynamic work lasting 8 hours. This suggests that high metabolic loads, as one component of physiological strain, should be avoided at work to prevent fatigue and low back pain injury. Recently, body worn assistive devices, also called exoskeletons, have been introduced in work environments to reduce risk factors for LBP [11]. These devices physically support the user when performing tasks that involve high back loads. Several studies found reduced low-back mechanical loading during lifting, bending and static holding tasks when using assistive devices that passively support the user’s trunk against gravity [12-15]. By reducing internal moments, and hence muscle activity around the low back, or by allowing different movement strategies, which would otherwise put too much load on the low back without exoskeleton, these exoskeletons might also reduce metabolic 4