Saskia Baltrusch

158 Chapter 6 In total, 26 male participants with a mean age, height, and body mass of mean (sd): 43.6years (7.7years), 177cm (7cm), and 82kg (12kg), participated in this study, including 18 from load-handling occupations. In addition, 6 employees from non-load-handling occupations were included. Data from two participants had to be discarded from the analysis, since these participants failed to understand instructions. Of all participants included in the analysis (N=24), we allocated 13 to the low back pain group and 11 to the healthy group. Our inclusion criteria for the pain group was a history of low-back pain and recurrent problems, defined as episodes of low-back pain more than once in their life. This criterion was assessed in a questionnaire with the questions 1) Have you ever had problems with the low back? (Yes/No) and 2) Have you had these problems only once or did they occur more often? (Once/More often). If participants answered “yes” and “more often” they were allocated to the low-back pain group. Participants who had low-back problems only once were allocated to the healthy group. To know the current pain level when starting the measurement, participants also had to answer the question 3) What is your current pain level? on a scale from 0=no pain to 10=maximum pain. The participants received an information letter prior to the experiment and signed an informed consent form on the measurement day. The experiment was approved by the medical ethical committee of VU medical center (VUmc, Amsterdam, The Netherlands, NL57404.029.16). 2.3 Functional performance test battery The test battery used for assessing functional performance with and without the exoskeleton was an adapted version of a test battery used previously [14], assessing objective and subjective performance (Table 1). The selected tasks in this test battery are divided into three categories: 1) functional tasks to assess the potential support of the exoskeleton (tasks 1-4), 2) functional tasks to assess potential hindrance by the device (tasks 5-8) and 3) tasks to assess the effect on range of motion when wearing the device (tasks 9-12). We adapted the task ‘Lifting’ in the current test battery, since we reached a ceiling effect in this task in our previous study [14], when assessing maximum weight that can be lifted. In the present study, we therefore assess the maximum number of lifts in 2 minutes with a weight of 20 kg. Additionally, we added the subjective outcome measure ‘Local Discomfort in the Lower Back’ for each task, since we expected participants with recurrent low-back pain to start with non-zero