Limitations
The trial also has several limitations. We recorded the number and characteristics of the patients who underwent the screening phase using the 6MWT. However, due to practical reasons, we could not record the number and characteristics of all patients who were considered for inclusion but did not enter the screening phase due to the presence of exclusion criteria 1 to 7. This limits the external generalizability of the trial.Another potential limitation is that phone support for all intervention patients is provided by only two research nurses who are closely associated with the research team and highly motivated. As the intervention impact likely depends on the quality of the phone support, the intervention effect can be reduced when the intervention is translated to routine clinical care, and nurses of various qualities and motivations will be recruited to provide the phone support. To investigate the potential impact of the varying phone support, we plan to conduct an exploratory analysis comparing patients allocated to either of the two research nurses.Finally, the trial was substantially affected by the COVID-19 pandemic, which had a significant impact on patients’ habitual physical activity [