Pregnancy has been shown to affect the quality, duration, and pattern of sleep (Paavonen et al., 2017; Reid et al., 2017). These changes have important implications, as insufficient sleep is associated with health problems and complications during labor. In line with studies investigating the general population, a few studies focused on pregnant smokers and have also shown a prevalence of sleep abnormalities (e.g., Danilov et al., 2022; Lange et al., 2018; Paavonen et al., 2017). Studies examining the role of passive smoking on sleep are rare, be it in the general population or in pregnant women. 

The aim of the Ciochon et al. study was to investigate the relationship between active or passive smoking and three types of sleep problems during pregnancy: difficulty falling asleep, difficulty staying asleep, and waking up too early. The authors hypothesized that pregnant women's exposure to smoking (active and passive) would increase their risk of sleep problems during pregnancy.

Participants were part of a larger study: the Corona Mums project, which included 3365 pregnant women from Poland, aged 18 to 43 years. These women completed an online questionnaire during the COVID-19 pandemic, from May 2020 to September 2021. The authors conducted multivariate logistic regressions that included the following control variables: socio-demographic, pregnancy-related variables, and psychological variables.

The results of the study showed that passive smoking is a risk factor for waking up too early, but they showed no evidence suggesting that active or passive smoking was related to any of the other sleep variables. The authors highlighted the roles of control variables included in the models. Specifically, sleep difficulties were related to age, place of residence, education, level of anxiety and depression in pregnant women, and the presence of nausea or vomiting. Further, in all the models, the level of anxiety, depression, and trimester of pregnancy (3rd trimester in comparison to 1st and 2nd) were significantly related to the risk of occurrence of sleep problems.

While only one of the six examined associations showed statistical significance, the findings are still useful in highlighting potential risks associated with passive smoking and sleep disturbances during pregnancy. The study also underscores the need for more comprehensive investigations, including direct measures of sleep quality, such as actigraphy or polysomnography, which are necessary to better understand the underlying mechanisms and to confirm the potential impacts of both active and passive smoking on sleep during pregnancy.

Exercise capacity is recognised as a strong predictor of mortality and cardiovascular morbidity in both healthy individuals and patients with coronary heart disease (Novaković et al., 2022). Accordingly, exercise-based cardiac rehabilitation is recommended as an effective secondary preventive intervention (Task Force Members et al., 2016; Anderson et al., 2016). While earlier studies generally focused on changes in exercise capacity during or immediately after rehabilitation (Uddin et al., 2016), recent research has emphasised the importance of physical activity trajectories on mortality in patients with coronary heart disease (Gonzalez-Jaramillo et al., 2022). This highlights the need to understand changes in exercise capacity and physical activity following the rehabilitation phase.

This study specifically explored changes in exercise capacity (assessed using the six-minute walking test) and physical activity (assessed using the International Physical Activity Questionnaire-Short Form) one year after a cardiac rehabilitation programme in patients with coronary heart disease. Additionally, the authors examined changes in motivation for physical activity over the 12 months following rehabilitation.

Within the limitations of its observational and monocentric nature, the study presents important findings that can inform future research, generate hypotheses, and guide the design of targeted trials aimed at improving or maintaining exercise capacity and physical activity levels after rehabilitation. The exploration of potential barriers to physical activity 12 months after rehabilitation could inform strategies to increase participation in physical activity post-rehabilitation, thereby improving survival (Moholdt et al., 2018).

This study is well-conducted and clearly presented. The authors' interpretation is balanced and consistent with the study's design and analysis. As noted by one of the reviewers, retention in cardiac rehabilitation studies is challenging, and the authors have done a commendable job in retaining participants. They have also addressed all the reviewers' concerns properly and accurately. I am pleased to recommend this preprint.