Badenes‑Bonet et al. BMC Pulmonary Medicine (2022) 22:340 https://doi.org/10.1186/s12890-022-02134-4 RESEARCH Open Access Predictors and changes of physical activity in idiopathic pulmonary fibrosis Diana Badenes‑Bonet1,2,4, Anna Rodó‑Pin1, Diego Castillo‑Villegas5, Vanesa Vicens‑Zygmunt6, Guadalupe Bermudo6, Fernanda Hernández‑González7, Karina Portillo8, Juana Martínez‑Llorens1,2,3,4, Roberto Chalela1,2,4, Oswaldo Caguana1, Jacobo Sellarés7, Maria Molina‑Molina3,6, Xavier Duran9, Joaquim Gea1,2,3,4, Diego Agustín Rodríguez‑Chiaradia1,2,3,4 and Eva Balcells1,2,3,4* Abstract Background: Different clinical predictors of physical activity (PA) have been described in idiopathic pulmonary fibro‑ sis (IPF), but studies are lacking evaluating the potential role of muscle strength and anxiety and depression symp‑ toms in PA limitation. Moreover, little is known about the impact of changes in PA in the course of the disease. The aim of the present study was to investigate the relationship between baseline PA and a wide range of variables in IPF, to assess its longitudinal changes at 12 months and its impact on progression free-survival. Methods: PA was assessed by accelerometer and physiological, clinical, psychological factors and health-related quality of life were evaluated in subjects with IPF at baseline and at 12 month follow-up. Predictors of PA were determined at baseline, evolution of PA parameters was described and the prognostic role of PA evolution was also established. Results: Forty participants with IPF were included and 22 completed the follow-up. At baseline, subjects performed 5765 (3442) daily steps and spent 64 (44) minutes/day in moderate to vigorous PA. Multivariate regression models showed that at baseline, a lower six-minute walked distance, lower quadriceps strength (QMVC), and a higher depres‑ sion score in the Hospital Anxiety and Depression scale were associated to lower daily step number. In addition, being in (Gender-Age-Physiology) GAP III stage, having a BMI ≥ 25 kg/m2 and lower QMVC or maximum inspiratory pressure were factors associated with sedentary behaviour. Adjusted for age, gender and forced vital capacity (FVC) (%pred.) a lower progression-free survival was evidenced in those subjects that decreased PA compared to those that main‑ tained, or even increased it, at 12 months [HR 12.1 (95% CI, 1.9–78.8); p = 0.009]. Conclusion: Among a wide range of variables, muscle strength and depression symptoms have a predominant role in PA in IPF patients. Daily PA behaviour and its evolution should be considered in IPF clinical assessment and as a potential complementary indicator of disease prognosis. Keywords: Physical activity, Idiopathic pulmonary fibrosis, Predictors, Muscle strength, Depression, Prognosis Introduction Idiopathic pulmonary fibrosis (IPF) is a progressive fibro- sing interstitial lung disease (ILD) with a high morbidity and mortality [1]. Exertional dyspnoea, the predominant *Correspondence: ebalcells@psmar.cat symptom in IPF, worsens as disease progresses and leads 1 Interstitial Lung Disease Unit, Respiratory Medicine Department, Hospital to exercise limitation and reduced levels of physical activ- del Mar, Passeig Marítim 25, 08003 Barcelona, Spain Full list of author information is available at the end of the article ity (PA) [2]. In this respect, objectively measured PA by © The Author(s) 2022. 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The Creative Commons Public Domain Dedication waiver (http://​creat​iveco​ mmons.​org/​publi​cdoma​in/​zero/1.​0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Badenes‑Bonet et al. BMC Pulmonary Medicine (2022) 22:340 Page 2 of 9 accelerometry is reduced in IPF patients, compared to health-related quality of life (HRQoL) and muscle healthy individuals, not only in advanced IPF but also in strength in IPF, and (b) to assess longitudinal changes earlier stages [3]. Furthermore, in several cross-sectional in their PA over 12 months. The secondary aim was studies, PA has been associated to different physiological to evaluate the impact of PA changes on progression variables [i.e. forced vital capacity (FVC), carbon mon- free-survival. oxide diffusing capacity ­(DLCO) and 6-min walked dis- tance (6MWD)], as well as patient-reported outcomes Methods such as dyspnoea, fatigue and quality of life [3–5]. How- Study population ever, other relevant parameters such as muscle strength Patients with IPF diagnosis were consecutively recruited or psychological factors have not been explored in detail from a specialized ILD clinic in five tertiary-teaching and, information regarding their contribution or impact hospitals. Exclusion criteria were relevant comorbidi- on PA in IPF patients is under-researched. ties which prevented PA measurement or the six-minute Additionally, there are few longitudinal studies that walking test (6MWT) performance, clinical worsening or have examined changes of PA over time in IPF patients hospital admission during two months prior to inclusion, [6, 7]. These studies have observed a significant annual severe pulmonary hypertension detected by echocar- decline in PA and have highlighted that this decline could diogram [8], treatment with corticosteroid therapy, be disproportionate to changes in classical physiological diagnosis of an active neoplasia or being included in a variables, such as lung function and exercise capacity. rehabilitation program. Moreover, the effects of PA in mortality or progression in IPF are controversial. Bahmer et al. [6] reported an inde- Study design pendent association between a lower baseline PA (i.e. This is a multicentre prospective study divided into two steps/day) adjusted by age, sex and antifibrotic therapy, phases (Fig. 1). Firstly, a cross-sectional evaluation was and a higher 3 year mortality risk. By contrast, in a more performed including clinical variables collection such recent study, neither baseline daily step count (DSC) nor as demographic, (Gender-Age-Physiology) GAP index, its 12 month decline were associated with long-term sur- body mass index (BMI), Charlson comorbidity index and vival [7]. diagnosis and treatment received. Pulmonary function The primary aims of our study were: (a) to investi- (PFTs), exercise capacity, respiratory and limb muscle gate the relationship between baseline PA and a wide strength and body composition were assessed and dysp- range of variables, including lung function, exercise noea, anxiety, depression and HRQoL questionnaires capacity, dyspnoea, anxiety and depression symptoms, were completed. Moreover, PA was assessed with an Fig. 1 Study flowchart. mMRC Modified medical research council; SGRQ St. George respiratory questionnaire; HADS Hospital anxiety and depression scale; PFTs Pulmonary function tests; 6MWT Six-minute walking test Badenes‑Bonet et al. BMC Pulmonary Medicine (2022) 22:340 Page 3 of 9 accelerometer. A follow-up evaluation was performed at strength (hand grip: JAMAR 030J1, Chicago, IL, USA) 12 months. and isometric quadriceps maximum voluntary contrac- The study was carried out according to the principles of tion (QMVC: BIOPAC dynamometer, BIOPAC Systems, the Declaration of Helsinki for human investigations and Schooner, CA, USA) were assessed following previ- approved by the local Ethics Committee with allocation ously described methodology [19]. The highest value of number 2017/7241/I. All participants signed the appro- three manoeuvres was recorded. Data were expressed as priate informed consent prior to their inclusion. absolute values and using validated reference equations [20–22]. Study variables PA measurement Follow‑up evaluation Participants were provided with a triaxial accelerometer The study participants were assessed after 12 months by (SenseWear Pro2 Armband, SWA; Body Media, Pitts- repeating the complete protocol. Progression-free sur- burgh, PA, USA) and were instructed to wear the moni- vival was assessed up to 24 months after inclusion, and toring device on their left triceps for 23 h a day, for 7 data were obtained from institutional records. A rela- consecutive days except for the time spent in personal tive decline of FVC > 10% and/or ­DLCO > 15% during the hygiene [9]. The minimum recording time for the analysis 24 month follow-up were considered as disease progres- was defined as at least 3 days, recording more than 70% sion [23, 24]. of the daytime (8–22 h), excluding the first and last day of the record [10]. Parameters of PA included DSC, daily minutes of Statistical analysis moderate-to-vigorous PA (MVPA ≥ 3 metabolic equiva- Categorical variables were expressed as number and per- lents [METS]) and sedentary time (< 1.5 METS) [10, centages, whereas continuous variables as mean (stand- 11]. PA level (PAL: total daily energy divided by sleeping ard deviation, SD), or median (25th and 75th percentiles, energy expenditure) was also registered and categorized. ­P25-P75) when normality assumption was not fulfilled. A An inactive person was defined as having a PAL < 1.40, multivariate linear regression model was built for each whereas a sedentary person as having a PAL 1.40–1.69, PA variable (DSC, time in MVPA and sedentary time). and an active person as having a PAL ≥ 1.70 [12]. Potential predictors including BMI, FFMI, FVC (%pred.), ­DLCO (%pred.), 6MWT (distance and ­SpO2), respiratory Dyspnoea, HRQoL and anxiety and depression and peripheral muscle strength, degree of dyspnoea, The modified Medical Research Council dyspnoea scale SGRQ and HAD score were identified from the literature. (mMRC) [13], the St. George Respiratory Questionnaire Covariates with a p-value < 0.1 were entered in the model, (SGRQ) [14] and the Hospital Anxiety and Depression and successively excluded if not associated with the out- Scale (HADS) [15] were completed as indicated. come (p < 0.05). Finally, the most parsimonious model that still explained the data was built for each outcome. Lung function and exercise capacity Longitudinal changes in PA were tested by paired t-test PFTs including forced spirometry (EasyOne, NDD Medi- or Wilcoxon signed-rank test as appropriate. Progres- cal Technologies, Zurich, Switzerland) static pulmonary sion free-survival analysis according to PA changes was volumes (body plethysmography), D ­ LCO (MasterLab, Jae- analysed by the Kaplan–Meier method. Cox proportional ger, Würzburg, Germany) [16, 17] and the 6MWT were hazard models were performed, adjusted for gender, performed according to international guidelines [18]. age and FVC (%pred.), for progression or mortality out- Arterial blood gas measurement at room air was also per- comes. A cut-off point of change of DSC was calculated formed (RapidLab500, Siemens, Erlangen, Germany). by maximally selected rank statistic and performed with the web-based tool Cutoff Finder [25]. This method takes Body mass and composition jointly into account the marker, the event as well as time Anthropometric variables including BMI and fat-free to event. A p-value < 0.05 was considered as statistically mass index (FFMI) (acquired by bioelectrical impedance; significant. The analysis was performed using the IBM BODYSTAT 1500, Bodystat Ltd, Isle of Man, UK) were SPSS statistics pack for Windows (Version 23.0, IBM obtained. Corp., Armonk, NY, USA). Respiratory and peripheral muscle strength Results Respiratory muscle strength [maximum inspiratory pres- Study participants sure (MIP), maximum expiratory pressure (MEP)] both Forty participants with IPF were enrolled from July 2017 measured at the mouth, as well as peripheral muscle to December 2019 (Table 1). Badenes‑Bonet et al. BMC Pulmonary Medicine (2022) 22:340 Page 4 of 9 Table 1 Clinical characteristics of the study population (n = 40) Table 1 (continued) anxiety and depression Total population (n = 40) § ΔSpO2%, percentage of change between baseline and exercise values Demographic ‡ TLC (n = 31), ­DLCO (n = 33), ­PaO2 (n = 33) Age (years) 71.4 (6.5) Gender: male 30 (75) The mean age (SD) at first evaluation was 71.4 (6.5) Smoking status: current or former smoker 29 (72.5) years, and 75% were males. The mean (SD) FVC % pred. Working status: active 3 (7.5) and ­DLCO % pred. was 79.2 (19.4) % and 44.7 (14.4) GAP index (stage I/II/III), (%) 35/40/25 %, respectively. Thirty patients (75%) were classified Diagnosis and treatment in GAP stages I-II. In the 6MWT, patients walked a Time since diagnosis (months), median (p25– 18.5 (11.2–42.6) p75) mean distance of 451.6 m (92.7%pred.) and showed a Ambulatory oxygen therapy 6 (15) mean ­SpO2 of 90%. Respiratory and peripheral muscle Antifibrotic therapy 30 (75) strength were roughly preserved in all subjects. Total Charlson comorbidity index, median (p25–p75) 4 (3–6) mean score in the SGRQ was 30.3 and HAD depression Lung function‡ and anxiety score were 6 and 5, respectively. FVC (% pred.) 79.2 (19.4) Of the 40 patients studied at baseline, 22 (55%) com- TLC (% pred.) 70.6 (14.6) pleted the follow-up. One patient died before study DLCO (% pred.) 44.7 (14.4) completion, 2 declined and 1 was included in a reha- PaO2 (mm Hg) 81.3 (8.7) bilitation program during the follow-up period. The 14 Exercise capacity (6MWT) remaining subjects were not included, as the 12 month Distance (m) 451.6 (92.7) PA measurement was to be completed during the Distance (% pred.) 96.2 (18.6) COVID-19 pandemic, and we considered PA and other Basal ­SpO2 (%) 95.1 (2.4) clinical data could be biased by the lockdown. Accord- Mean ­SpO2 (%) 90.1 (5.8) ingly, all PA measurements were performed prior to Minimum ­SpO2 (%) 87.5 (6.5) COVID-19 pandemic to avoid confounders. ΔSpO2 (%), median (p25–p75)§ 7 (4–12.8) Muscular strength MIP (% pred.) 87.6 (26.3) Baseline PA parameters and their predictors MEP (% pred.) 75.3 (23.7) At baseline, subjects performed 5765 (3442) daily steps Non-dominant hand-grip (kg) 30.8 (9.3) and spent 64 (44) minutes/day in MVPA. The mean Non-dominant hand grip (% pred.) 113.4 (19.7) sedentary time was 725 (44) minutes/day. Accord- QMVC (kg) 33.6 (9.9) ing to PAL, 45.9% of the patients were inactive, 43.2% QMVC (% pred.) 91.9 (25.2) sedentary and 10.8% active. A lower 6MWD, lower Body mass and composition QMVC, and a higher depression score were associated BMI (kg/m2) 27.4 (4.6) to lower DSC. Sedentary behaviour was associated to FFMI (kg/m2) 17.8 (2.1) the presence of GAP III stage, a BMI ≥ 25 kg/m2 and a Symptoms, HRQoL and psychological factors low QMVC or MIP. A lower time spent in MVPA was Dyspnoea (mMRC 0–4), median (p25–p75) 1 (0.25–2) related to a lower QMVC or MIP (Table 2). SGRQ score (0–100) Total 30.3 (20.1) Activity 48.2 (24.2) Longitudinal changes in PA Symptoms 34.4 (22.4) Impact 27.5 (20.8) There were no significant differences in baseline char- HAD scale (0–21) acteristics or PA variables between completers and Anxiety 6 (3.6) non-completers except in the anxiety score, which was Depression 5 (4.4) higher in the non-completer group. DSC decreased by a mean of − 789 (p = 0.054). The increase in sedentary Data are presented as mean (SD) and n (%) unless otherwise specified time was of 17.5 min/day (p = 0.073). No statistically GAP Gender-age-physiology; FVC Forced vital capacity; TLC Total lung capacity; DLCO Carbon monoxide diffusion capacity; PaO2 Arterial oxygen partial significant changes were observed in MVPA [9.1 min/ pressure; 6MWT Six-minute walking test; SpO2 Peripheral oxygen saturation; day; p = 0.256], neither in PAL categories (p = 0.513) MIP Maximum inspiratory pressure; MEP Maximum expiratory pressure; QMVC Quadriceps maximum voluntary contraction; BMI Body mass index; FFMI Fat- (Fig. 2). Regarding changes in other clinical and func- free mass index; HRQoL Health-related quality of life; mMRC Modified medical tional variables, only ­ DLCO and S ­pO2 during the research council; SGRQ St. George respiratory questionnaire; HAD Hospital 6MWT had significant changes over 12 months. Badenes‑Bonet et al. BMC Pulmonary Medicine (2022) 22:340 Page 5 of 9 Table 2 Independent predictors of physical activity parameters (daily steps, sedentary time, and time in MVPA) in 40 IPF patients at baseline Variables Steps per day Sedentary time (mins/day) Time in MVPA (mins/day) β (95% CI) p β (95% CI) p (β 95% CI) p GAP: stage III – – − 27.9 (− 52.6, − 3.2) 0.028 – – 6MWD (m) 13.7 (4, 23.5) 0.007 – – – – MIP (%pred.) – – − 0.89 (− 1.3, − 0.47) < 0.001 0.88 (0.47,1.3) < 0.001 QMVC (%pred.) 41.7 (7.2, 76.2) 0.019 − 0.57 (− 1.02, − 0.11) 0.016 0.69 (0.23, 1.14) 0.004 BMI: ≥ 25 (kg/m2) – – 24.5 (0.32, 48.7) 0.047 – – HADS score (depression) − 214.6 (− 416.6, − 12.5) 0.038 – – – – Adjusted ­R2 0.455 0.561 0.470 GAP index was dichotomized to GAP I-II and GAP III. BMI was dichotomized by BMI < 25 and ≥ 25 Each column is a single multivariate lineal regression model including as covariates the variables that show a coefficient in each column. Degree of dyspnoea, FVC %pred., Total SGRQ score and HAD anxiety score, were tested as potential predictors, and finally not included because they were not independently related to the outcome, nor modified estimates for the remaining variables MVPA Moderate to vigorous physical activity; 6MWD Six-minute walked distance; QMVC Quadriceps maximum voluntary contraction; HADS Hospital anxiety and depression scale; GAP Gender-age-physiology; MIP Maximum inspiratory pressure; BMI Body mass index Fig. 2 Physical activity parameters at baseline and 12 month follow-up (n = 22). Bars graph show the mean and standard deviation. PA Physical activity; MVPA Moderate to vigorous physical activity Progression free‑survival analysis adjusting for age, sex and FVC (%pred.) [HR 12.1 (95% Patients who died or progressed had a poor lung CI 1.9–78.8); p = 0.009]. function, a higher 6MWT desaturation, higher GAP score at baseline, and a higher DSC decline over Discussion 12 months than free-progression survivors (1769 vs. The main findings of the present study are that quadri- − 28; p = 0.016). The optimal cut-off point of DSC ceps strength and psychological factors (depression) were was -895 steps for predicting the 24 month progres- identified as novel independent predictors of PA in IPF sion-free survival. Kaplan–Meier curves showed that patients. Moreover, the DSC decline at 12 months was patients who reduced their PA ≥ 895 steps per day had marked; with the 895 daily step threshold being a good a lower progression-free survival than those who did discriminant of free-progression survival. not [18.4 months (95%CI, 15.6–21.2) vs. 22.5 (95%CI In the present study, PA behaviour was not always con- 20.6–24.4); p = 0.004] (Fig. 3). In the Cox regression, sistent with previous literature. In this regard, a higher a change ≥ to this cut-off point, was associated with a DSC was related to a higher 6MWD, being consistent higher progression or mortality risk at 24 months after with previous studies [3, 5, 26]. By contrast, we observed Badenes‑Bonet et al. BMC Pulmonary Medicine (2022) 22:340 Page 6 of 9 results are in line with the above-mentioned studies, as we found no clear respiratory muscle impairment in our population, although a mild relationship was identified between MIP and PA intensity. One possible explanation could be PA avoidance, leading to deconditioning and muscle wasting. Moreover, mechanical diaphragmatic restraints, could increase the work of breathing result- ing in a chronic overload, but this would probably have more impact in muscle endurance that in strength. In this regard, this increased load in respiratory muscles, added to rapid shallow breathing, could increase breathless- ness and contribute to reduce PA. In view of the present results, we believe that peripheral and respiratory muscle strength assessment could be of potential interest, and, mainly to direct training strategies to improve exercise Fig. 3 Kaplan–Meier progression-free survival curves at 24 months tolerance, dyspnoea, and consequently PA. in IPF patients who decline ≥ 895 steps/day and those who do not Additionally, our study showed that a higher depression decline (n = 22). IPF idiopathic pulmonary fibrosis score was independently associated with a lower DSC. In other chronic lung diseases such as COPD, depres- sion symptoms have been prospectively associated with no association between any PA parameter and lung func- a reduction in PA at 6 month follow-up [35]. Specifically tion, as reported by previous research. A relevant and in ILD, a recent longitudinal study evidenced that depres- novel finding of our study was that quadriceps strength sive symptoms showed a trend towards significance at was independently associated with the amount and inten- predicting reduced baseline DSC when adjusting for age, sity of PA, as well as with sedentary time. The relation- smoking status and lung function [36]. According to our ship between peripheral muscle dysfunction and reduced results, psychological status could have an influence on PA, is well-documented in other respiratory disorders, PA in IPF subjects, and therefore, psychological assess- but has never been reported specifically in IPF [27, 28]. ment should be considered, to better target areas that can In ILD, previous research was focused on the role of potentially impact on PA levels. quadriceps strength on exercise capacity and not on The mean decline in DSC after 12 months in our study PA, and has the limitation that included heterogeneous was relevant and somewhat different from previous groups of ILD patients [29, 30]. Factors such as ageing, observations. To our knowledge, only two previous stud- hypoxia, oxidative stress, malnutrition and decondi- ies have focused on changes of PA in IPF, and the popula- tioning due to reduced PA levels, could be associated to tion profile, design, and outcomes of each study must be potential peripheral muscle dysfunction in IPF, but stud- considered when comparing to our data. ies determining its specific causes and pathophysiological Prasad et al. [7] observed a slightly lower decline in mechanisms are lacking [31]. DSC after 12 months follow-up in 37 IPF patients. A In a similar direction, our results evidenced that a possible confounder in this study could be the inclusion lower MIP was related to a lower time spent in MVPA of lung transplant candidates; and their participation in and a higher sedentary time. It is well established that rehabilitation programs. In addition, Bahmer et al. [6] patients with ILD present a progressive decrease in lung reported almost a 50% decline in DSC in 3 years, of 23 function, lung compliance and an increase in elastic survivors of an initial cohort of 46 IPF patients. Surpris- load, secondary to fibrosis. Consequently, the predomi- ingly, the annual decline in PA was higher than in our nant symptom is exertional dyspnoea, which leads to a study, despite our patients had similar lung function and reduced exercise capacity. Accordingly, several studies a lower baseline PA. Nevertheless, their study provided have evaluated respiratory muscle strength in ILD, point- no information about other PA parameters. Another rele- ing out that the chest mechanical properties remain sta- vant aspect observed in our study was that the PA decline ble without relationship with lung volume reduction [32, was not accompanied by significant changes in other 33] until advanced stages of the disease. Moreover, recent physiological parameters, such as FVC or 6MWD. This diaphragmatic ultrasound studies, evidence a reduced could be partially explained by the short follow-up period mobility and diaphragmatic thickness during deep and clinical profile of our population (i.e. mild FVC inspiration in ILD subjects compared with healthy indi- impairment, preserved 6MWD, and a high percentage of viduals, showing no differences in its strength [34]. Our patients treated with antifibrotic therapy). Together, our Badenes‑Bonet et al. BMC Pulmonary Medicine (2022) 22:340 Page 7 of 9 observations are in line with previous studies that sup- assessment should be considered. Finally, it describes port the idea that the PA decline could be prior to pul- change in DSC as a potential progression or mortality monary function or exercise capacity deterioration, being predictor in IPF, suggesting that PA monitoring could dependent of other factors as disease progresses, and be a complementary marker of progression to lung therefore its longitudinal evaluation could be a comple- function and exercise capacity, which should be con- mentary tool when evaluating IPF progression [6]. sidered in clinical practice. Further longitudinal stud- Finally, we evaluated the prognostic value of PA ies are needed to study the predictors of PA changes changes over 12 months. To our knowledge, our study and in its prognostic role in IPF, beyond traditional is the first to show a threshold for longitudinal changes prognostic factors. of DSC (measured by accelerometer) in predicting pro- gression or mortality. There is little and controversial Abbreviations information on the effects of PA in robust outcomes in 6MWD: Six-minute walked distance; 6MWT: Six-minute walking test; BMI: IPF, and it focuses mainly on baseline assessment of Body mass index; DLCO: Carbon monoxide diffusing capacity; DSC: Daily step PA. Bahmer et al. [6] reported an independent associa- count; FFMI: Fat-free mass index; FVC: Forced vital capacity; GAP: Gender- age-physiology; HADS: Hospital anxiety and depression scale; HRCT​: High tion between a lower baseline DSC (adjusted by age, sex resolution computed tomography; ILD: Interstitial lung disease; IPF: Idiopathic and antifibrotic therapy) and a higher risk of mortality at pulmonary fibrosis; MEP: Maximum expiratory pressure; METS: Metabolic 3 years. Moreover, Shingai et al. [37] demonstrated that equivalents; MIP: Maximum inspiratory pressure; mMRC: Modified medical research council; MVPA: Moderate to vigorous physical activity; PA: Physical DSC was a good predictor of 1 year mortality in 87 IPF activity; PAL: Physical activity level; PFTs: Pulmonary function tests; QMVC: patients at the time of diagnosis and, additionally they Quadriceps maximum voluntary contraction; HRQoL: Health-related quality of first established a cut-off point (3473 steps) for predicting life; SGRQ: Saint George respiratory questionnaire. mortality. By contrast, Prasad et al. [7] observed no asso- ciation between baseline daily steps count or its decline Supplementary Information over 12 months with better long-term survival. The online version contains supplementary material available at https://​doi.​ org/​10.​1186/​s12890-​022-​02134-4. Some limitations of our study should be mentioned. Firstly, the relatively small sample size, especially during Additional file 1: Table S1. General characteristics of subjects that com‑ the follow-up. However, the percentage of patients lost pleted and not completed follow-up. to follow-up is comparable to previous publications and Additional file 2: Table S2. Longitudinal changes in lung function, exer‑ furthermore there were no differences between those cise capacity, muscle strength, body mass and composition, dyspnoea, quality of life and psychological factors in IPF patients (n=22). lost and those that completed the follow-up. Further and Additional file 3: Table S3. General characteristics at baseline of subjects larger prospective studies to validate the prognostic role that completed follow-up by progression-free survival** at 24 months of the 895 DSC threshold should be considered. Sec- (n=22). ondly, the present study cannot establish the direction of Additional file 4: Table S4. Longitudinal characteristics (changes in the relationships among PA and its predictors. Thirdly, parameters) * by progression-free survival** at 24 months. our study population came from a specific geographical area and our results cannot be generalized to countries Acknowledgements with different cultural determinants. Despite these limi- Laura Gutiérrez Martín and Concepción Ballano Castro. Respiratory Medicine Department, Hospital del Mar, Barcelona, Spain. tations, our study had many strengths. It is multicentric and has included a wide range of variables as potential Author contributions PA predictors, reflecting physiological, psychological and DB-B, PhD: Design and methodology, acquisition of funding, visits perfor‑ mance, data collection, data analysis and writing. AR-P, Physiotherapist: Visits QoL aspects in IPF patients. Finally, we explored other performance, data collection and writing. DCV, PhD: Design and methodol‑ predictors of PA variables beyond DSC, such as PA inten- ogy, expertise and feedback. VV-Z, PhD: Design and methodology, expertise sity and sedentary behaviour. and feedback. GB, MD: Design and methodology, expertise and feedback. FH-G, PhD: Design and methodology, expertise and feedback. KP, PhD: Design and methodology, expertise and feedback. JML, PhD: Expertise, writing and Conclusions feedback. RC, PhD: Expertise, writing and feedback. OAC, MD: Expertise, writ‑ ing and feedback; JS, PhD: Design and methodology, expertise and feedback. In summary, our study identifies muscle strength and MM-M, PhD: Design and methodology, expertise and feedback. XD, Statistic: psychological factors as novel PA predictors in IPF, Data analysis. JG, PhD: Expertise, feedback, acquisition of funding and writ‑ being both modifiable factors with interventions. ing. DAR, PhD: Design and methodology, expertise, feedback, acquisition of funding and writing. EB, PhD: Design and methodology, expertise, feedback, These findings suggest potential aspects that can be acquisition of funding and writing. All authors read and approved the final targeted to improve PA in IPF patients from the diag- manuscript. nosis, and support the need for early inclusion in Funding rehabilitation programs, including respiratory and This study was supported by SEPAR 2017 (Fellowship) and Rio Hortega; ISCIII peripheral muscle training. Moreover, psychological (Project and fellowship). Badenes‑Bonet et al. BMC Pulmonary Medicine (2022) 22:340 Page 8 of 9 Availability of data and materials 10. Waschki B, Kirsten A, Holz O, Müller KC, Meyer T, Watz H, et al. Physical The datasets supporting the conclusions of this article are included within activity is the strongest predictor of all-cause mortality in patients with the article (and its additional files). Further enquiries can be directed to the COPD: a prospective cohort study. 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