Sample size calculation
Sample size calculation was based on the primary research question (i.e. effectiveness of the intervention on daily step count). To obtain a power of 80%, expecting a drop-out rate of 20%, a total of 82 patients needed to be included in this study (based on a between group difference of 1785 steps/day, SD of 2505 and α-level of 0.05). These data were based on preliminary results of the tele coaching study running in our center [