Saskia Baltrusch

117 Chapter 5 1 Introduction Lower Back Pain (LBP) and shoulder pain affects more than 40% of the working population in the EU [1]. Mechanical loading has been identified as an important risk factor to develop LBP [2]. Especially, compression forces on the lumbar spine are one of the main risks, as reflected in the NIOSH standard for lifting [3]. Despite these insights, many workers are still exposed to mechanical loading: More than 40% of the workers in the EU are working in tiring and painful positions, while more than 30% are required to lift heavy loads at least a quarter of the work time [1]. Besides the health risks for the workers, these numbers also have quite severe financial implications: Cost estimates for health expenditure, caused by lower back pain range from 116 € per capita in Belgium up to 209 € per capita in Sweden [4]. This means, that for a relatively small country like Belgium with a population of approximately 11 million inhabitants, the total costs caused by lower back pain are as high as 1.2 billion €, which corresponds roughly to 2% of the gross domestic product of Belgium. It is therefore not surprising, that cranes [5], hoist and other means to bypass the loading of the back have been developed. However, the use of cranes and hoists and other, on site mounted means, is often infeasible due to space restrictions or not practical [6]. Therefore, more recently, exoskeletons [7] have been developed to mitigate the health risk for workers and to reduce the cost caused by injuries. Over the last decades, several exoskeletons specifically designed to support workers have been developed: These range from exoskeletons for shoulder, lower back and leg support to exoskeletons, that support the entire body. For an extensive overview of the state of the art, the interested reader is directed to a review article of de Looze et al. (2016) [7]. Biomechanical considerations suggest, that the lumbo- sacral (L5-S1) region experiences peak mechanical loading in a wide range of tasks, specifically large compression forces of the spine [2]. These forces can range up to 5000 N or more when lifting a 15 kg load [8]. They are mainly due to muscle forces, needed to counteract the moment at the lower back, induced by gravitational forces on the upper body and load (Figure 1A). Therefore, the majority of the exoskeletons and exosuits focus on reducing compression forces in the lumbo-sacral region, by lowering the muscle forces that are required for lifting or holding of a static trunk posture. In almost all designs, this is achieved 5