Saskia Baltrusch

95 Chapter 4 between subsequent left heel strikes, correcting for speed of the treadmill and duration of the stride. Heel strikes were also used to define gait cycles for the EMG data, which were normalized to cycle time and averaged over cycles. 2.6 Statistics To test for the effect of exoskeleton use on selected dependent variables, we conducted one-way repeated-measures ANOVAs. We a-priori decided not to test for the main effect of lifting height or walking speed and their interaction with exoskeleton. Thus, we conducted two separate ANOVAs for each of the lifting heights (knee and ankle height) and two separate ANOVAs for each walking speed (PWS and PWSX). Hence, for the lifting task these ANOVAs included 1 factor (exoskeleton) with 3 levels (high-cam Laevo, low-cam Laevo, control condition without). For walking the ANOVAs included one factor (exoskeleton) with 2 levels (low-cam Laevo, control condition without). In case of a significant effect of exoskeleton in the lifting experiment, Bonferroni post-hoc tests were conducted to determine differences between exoskeleton conditions. Alpha of 0.05 was used as the critical level of significance. All statistical analyses were performed using SPSS for Windows (IBM, SPSS Statistics 23.0, USA). To test for statistically significant differences in muscle activity, we used one-dimensional statistical parametric mapping (SPM1D) [27] to perform a SPM1D repeated measure ANOVA between the exoskeleton conditions high-cam Laevo, low-cam Laevo and control for lifting and low-cam Laevo and control for walking. This analysis uses random field theory to make statistical inferences on the time intervals over which the independent variable (exoskeleton use) has a significant effect on muscle activity. In view of some loss of individual data for different outcome measures, the number of participants (N) included in the statistical calculation is reported for each outcome. 3 Results Metabolic costs and underlying changes in movement strategies and muscle activity are reported first for lifting, followed by walking. 4