Saskia Baltrusch

56 Chapter 3 2.5 Outcomes The functional performance was measured based on objective and subjective outcome measures. In this way, not only the objective performance with the device, but also the user experience of working with the trunk exoskeleton could be assessed. Objective outcome measures For tests 1,2 and 5-8 the participant was instructed to perform the task “as fast as possible, but still in a safe and comfortable way”. Time recording, by means of a stopwatch, started when the researcher said “go” and stopped when the participant finished the task (see Table 1). Since tests 11 and 12 were chosen to assess the range of motion in terms of subjective experience only, no objective outcomes were measured. The simple manual task that was performed for tests 3 and 4 was a sorting task, in which the participant had to sort colored confetti by color into rows of ten. This task was chosen, because it can be done at any speed for 5 minutes and requires a high precision. Before the static holding tasks, the participants were instructed to choose a comfortable posture to ensure that they used the device in the correct way. They were not allowed to change that posture during the task but were allowed to stop at any time due to local discomfort in the lower back. Subjective outcome measures The subjective outcome measures were all assessed by using a visual-analog scale (VAS). A visual-analog scale is considered to allow a finer distinction between participants opinion by reducing the variation of individual interpretation compared to numerical rating scales [19]. Perceived task difficulty: After each task, the participant was asked to indicate the perceived difficulty of the task on the VAS, ranging from “very easy” to “very difficult”, with the question: “How difficult was the task you just performed?”. This VAS was presented on paper and the participant had to place a cross on the scale. The perceived task difficulty was assessed in both conditions.