Saskia Baltrusch

88 Chapter 4 load. Consequently, these exoskeletons might reduce fatigue and as such reduce this risk factor for injury. A few studies have evaluated the effect of a body worn lifting device on metabolic load during lifting. Whithfield et al. (2014) [16] found that an on-body personal lift augmentation device (PLAD) reduces musculoskeletal effort but does not affect oxygen consumption during a continuous lifting task. Additionally, no change in lifting technique or movement strategy was found. Whithfield et al. (2014) [16] suggested that this may be because some muscles got assisted by the device, while other muscle groups had to work harder. In the study of Sadler et al. (2011) [17] greater ankle and hip flexion and less lumbar and thoracic flexion were found when wearing the PLAD system, indicating a change of lifting technique from a stoop lift to a “semi-squat” technique. This change in technique could coincide with an increase in metabolic costs. Squat lifting has been found to involve higher metabolic costs than stoop lifting [18,19] due to higher muscle activity [20] to make the body move through a larger range of motion, requiring more mechanical work. The increased metabolic costs associated with this change in technique might offset the potential reduction in metabolic costs from the unloading effect of the exoskeleton on the back muscles. This could account for the observed lack of change in metabolic costs while using the PLAD system. However, so far, the metabolic benefits (or costs) of only one passive trunk exoskeleton have been tested and thus, results cannot be generalized to other lifting devices. Although potential positive effects of exoskeletons on mechanical and metabolic load are expected for specific load handling tasks, potential side effects of these devices on other tasks that need to be performed during working should not be ignored. Since workplaces nowadays are more versatile due to job rotation and automation [21] a high variety of tasks beyond manual material handling and lifting is observed in work environments. In a previous study [22], it has been established that tasks that involve large ROM (range of motion) of trunk or hip flexion, including walking, can be hindered by a trunk exoskeleton and are perceived as more difficult to perform with an exoskeleton. Participants also used a slower speed when walking with the exoskeleton. Thus, a device that supports the low back during lifting might require more muscle activity and hence increase metabolic costs during tasks such as walking.