To the Editor:

We read with great interest the article on a randomized controlled trial conducted by Bayram et al. [1]. Their study suggests that in hematopoietic stem cell transplant recipients, structured pulmonary rehabilitation (PR) programs and inspiratory muscle training (IMT) added to PR can maintain maximal exercise capacity, maximal pulmonary function, and quality of life (QOL). However, we have two concerns regarding this study.

First, it should be noted that the primary outcome registered in the registry was peak-VO2 [2], and the sample size calculation was also conducted using peak-VO2 data, making it the primary outcome of this study. Although we considered peak-VO2 data as the true primary outcome, we can conclude that the present intervention reduced peak-VO2 in both groups, and there were no significant differences between the groups, making it impossible to determine whether additional IMT for PR would have an effect on peak-VO2. Additionally, caution should be exercised in interpreting the results regarding other outcomes. With respect to the possibility of maintaining pulmonary function and QOL as stated in the conclusions, it is not possible to determine whether this is an effect of the PR programs or a natural progression, as there is no control group for no intervention.

Second, the authors’ article questions how effective the training was, given the small number of sessions in which IMT was carried out. In a previous study published in this journal [3], the number of sessions of IMT training was 8.0 ± 2.9 and adherence levels were considered good if at least 70% of the scheduled sessions were conducted. The authors reported a median value of 5 (minimum 2 to maximum 16) [1]. In order for the reader to accurately understand the results of this study, the relationship between the number of sessions undertaken and physical functioning, such as peak-VO2, needs to be clarified. Presenting the differences in changes in physical function between the group that attended more sessions and the group that attended fewer sessions would help readers understand the effects of IMT.