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Test-retest reliability, agreement and construct validity of the International Physical Activity Questionnaire short-form (IPAQ-sf) in people with COPD

  • Sofia Flora
    Affiliations
    Center for Innovative Care and Health Technology (ciTechCare), Polytechnic of Leiria, Leiria, Portugal
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  • Alda Marques
    Affiliations
    Lab 3R – Respiratory Research and Rehabilitation Laboratory, School of Health Sciences (ESSUA) and Institute of Biomedicine (iBiMED), University of Aveiro, Aveiro, Portugal
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  • Nádia Hipólito
    Affiliations
    Center for Innovative Care and Health Technology (ciTechCare), Polytechnic of Leiria, Leiria, Portugal
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  • Nuno Morais
    Affiliations
    Center for Innovative Care and Health Technology (ciTechCare), Polytechnic Institute of Leiria; School of Health Sciences, Polytechnic Institute of Leiria, Centre for Rapid and Sustainable Product Development (CDRSP), Polytechnic Institute of Leiria, Leiria, Portugal
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  • Cândida G. Silva
    Affiliations
    Center for Innovative Care and Health Technology (ciTechCare), Polytechnic Institute of Leiria, School of Health Sciences, Polytechnic Institute of Leiria, Coimbra Chemistry Centre, Department of Chemistry, University of Coimbra, Coimbra, Portugal
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  • Filipa Januário
    Affiliations
    Physical Medicine and Rehabilitation Department, Leiria Hospital Center, Leiria, Portugal
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  • Fátima Rodrigues
    Affiliations
    Institute of Health Environmental, Faculty of Medicine, University of Lisbon, Pulmonary Rehabilitation Unit, Hospital Pulido Valente, University Hospital Center North Lisbon, Lisboa, Portugal
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  • Bruno P. Carreira
    Affiliations
    Center for Innovative Care and Health Technology (ciTechCare), Polytechnic of Leiria, School of Health Sciences, Polytechnic of Leiria - Leiria; Unidade de Saúde Familiar Pedro e Inês, ACES Oeste Norte, Alcobaça, Portugal
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  • J. Cruz
    Correspondence
    Corresponding author. Center for Innovative Care and Health Technology (ciTechCare), School of Health Sciences (ESSLei), Polytechnic of Leiria, Campus 2, Morro do Lena, Alto do Vieiro, Apartado 4163, 2411-901, Leiria, Portugal.
    Affiliations
    Center for Innovative Care and Health Technology (ciTechCare), Polytechnic of Leiria; School of Health Sciences, Polytechnic of Leiria, Leiria, Portugal
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Open AccessPublished:December 07, 2022DOI:https://doi.org/10.1016/j.rmed.2022.107087

      Highlights

      • The IPAQ-sf presented good test-retest reliability results but wide limits of agreement.
      • The wide LoA suggest that it may not be appropriate to assess patients' PA levels throughout time.
      • Overall, the IPAQ-sf showed positive and moderate correlations with accelerometry.
      • The IPAQ-sf seems to be valid in COPD but caution on its widespread use is recommended as its specificity is low.

      Abstract

      Introduction

      This study assessed the test-retest reliability/agreement and construct validity of the International Physical Activity Questionnaire short-form (IPAQ-sf) in patients with chronic obstructive pulmonary disease (COPD). It also explored differences in its validity according to age, sex and GOLD airflow obstruction levels.

      Methods

      62 participants (68 ± 8 years, 53 males, FEV1 51 ± 23%pred) completed the Portuguese IPAQ-sf, wore an accelerometer for 7 days and completed a second IPAQ-sf. Test-retest reliability/agreement was assessed with Intraclass Correlation Coefficient (ICC2,1), 95% Limits of Agreement (LoA), standard error of measurement (SEM) and minimal detectable change (MDC95) for continuous variables, and percentage of agreement (%agreement) for categories (“active”/“inactive”). Validity was assessed with 95% LoA and Spearman's correlations (ρ) between IPAQ-sf 2 (METs-min/week, time in vigorous [VPA], moderate PA [MPA] and walking) and accelerometry (time in MVPA, VPA, MPA and step counts) for continuous variables; %agreement, Cohen's kappa, and sensitivity specificity and±predictive values for categories. Correlations were also performed for age, sex and GOLD airflow obstruction grades.

      Results

      Reliability was good (ICC2,1 = 0.707) with wide LoA (-6446—6409 METs-min/week). SEM and MDC95 were 1840 and 4971 METs-min/week, respectively. %agreement between the two IPAQ-sf was 84% (kappa = 0.660). Positive, moderate and significant correlations were found between IPAQ-sf and accelerometry (0.396 ≤ ρ ≤ 0.527, p < 0.001), except for VPA (p > 0.05). The strongest correlations were found in age (<65 years) and male (0.466 ≤ ρ ≤ 0.653, p < 0.05). %agreement between tools was 65% (kappa = 0.313), with high sensitivity (0.830) but low specificity (0.500).

      Conclusions

      The IPAQ-sf seems valid to be used in COPD but caution on its widespread use is recommended as its accuracy may be limited.

      Keywords

      Abbreviations' list

      ACSM
      American College of Sports Medicine
      BMI
      Body mass index
      CCI
      Charlson Comorbidity Index
      CI
      Confidence Intervals
      ciTechCare
      Centre for Innovative Care and Health Technology
      COPD –
      Chronic Obstructive Pulmonary Disease
      COSMIN
      COnsensus-based Standards for the selection of health Measurement INstruments
      FEV1
      Forced Expiratory Volume in first second
      GOLD
      Global Initiative for Chronic Obstructive Lung Disease
      ICC
      Intraclass Correlation Coefficient
      IPAQ-sf
      International Physical Activity Questionnaire short-form
      LoA
      Limits of agreement
      MDC95
      Minimal detectable change
      METs
      Metabolic equivalents
      mMRC
      modified Medical Research Council dyspnoea scale
      MPA –
      moderate physical activity
      MVPA
      Moderate and vigorous physical activity
      NPV
      Negative predictive value
      PA –
      Physical Activity
      PAR
      Stanford Seven-Day Physical Activity Recall
      PPV –
      Positive predictive value
      SD
      Standard deviation
      SEM
      Standard error of measurement
      SPSS
      Statistical Package for the Social Sciences
      VPA –
      vigorous physical activity
      WHO
      World Health Organisation

      1. Introduction

      People with chronic obstructive pulmonary disease (COPD) are markedly inactive in daily life [
      • Vorrink S.N.W.
      • et al.
      Level of daily physical activity in individuals with COPD compared with healthy controls.
      ] which contributes to a worsening of lung function, health status [
      • Waschki B.
      • et al.
      Disease progression and changes in physical activity in patients with chronic obstructive pulmonary disease.
      ], increased risk of acute exacerbations, hospitalizations and mortality in this population [
      • Watz H.
      • et al.
      An official European Respiratory Society statement on physical activity in COPD.
      ]. Physical activity (PA) is a modifiable factor with potential to improve COPD prognosis, therefore the latest Global Initiative for Chronic Obstructive Lung Disease (GOLD) guidelines [
      Global strategy for the diagnosis management and prevention of COPD, Global Initiative for Chronic Obstructive Lung Disease (GOLD).
      ] have underlined the importance of assessing and promoting regular PA as part of COPD management.
      The International Physical Activity Questionnaire short-form (IPAQ-sf) is one of the most widely used self-reported questionnaires to assess PA. Although good measurement properties were reported in the healthy population of the original study [
      • Craig C.L.
      • et al.
      International physical activity questionnaire: 12-country reliability and validity.
      ], measurement properties are population-specific. In fact, a systematic review has shown that studies assessing the validity of this instrument presented conflicting results, suggesting that evidence to support its use as an indicator of PA is weak [
      • Lee P.H.
      • et al.
      Validity of the international physical activity questionnaire short form (IPAQ-SF): a systematic review.
      ]. Moreover, poor validity results have also been found in populations with chronic conditions, such as in rheumatoid arthritis [
      • Tierney M.
      • Fraser A.
      • Kennedy N.
      Criterion validity of the international physical activity questionnaire short form (IPAQ-SF) for use in patients with rheumatoid arthritis: comparison with the SenseWear armband.
      ], fibromyalgia [
      • Kaleth A.S.
      • et al.
      Validity and reliability of community health activities model program for seniors and short-form international physical activity questionnaire as physical activity assessment tools in patients with fibromyalgia.
      ] or systemic lupus erythematosus [
      • Ahn G.E.
      • et al.
      Self-reported and objectively measured physical activity in adults with systemic lupus erythematosus.
      ]. In COPD, the IPAQ-sf has been used in several studies to estimate patients' PA levels [
      • Nyssen S.M.
      • et al.
      Levels of physical activity and predictors of mortality in COPD.
      ,
      • Saglam M.
      • et al.
      Functional capacity, physical activity, and quality of life in hypoxemic patients with chronic obstructive pulmonary disease.
      ,
      • Voncken-Brewster V.
      • et al.
      A randomized controlled trial evaluating the effectiveness of a web-based, computer-tailored self-management intervention for people with or at risk for COPD.
      ]. This study showed strong, positive and significant correlations between the IPAQ-sf METs-min/week and moderate and vigorous physical activity (MVPA) measured with an accelerometer (r = 0.729, p = 0.017), but low percentage of agreement (% agreement) in identifying “physically active” and “physically inactive” patients (% agreement = 20%, kappa = −0.538), and poor to moderate test-retest reliability (Intraclass Correlation Coefficient [ICC] = 0.439, 95% Confidence Intervals [95%CI] −0.267 — 0.838). The small sample size of this study hinders the generalisability of the findings. Further research is therefore needed to assess the measurement properties of the IPAQ-sf in COPD. Furthermore, previous studies have shown differences in PA levels among GOLD airflow obstruction levels [
      • Zogg S.
      • et al.
      Differences in classification of COPD patients into risk groups A-D: a cross-sectional study.
      ], and an influence of age and sex in patients’ PA behaviour [
      • Gimeno-Santos E.
      • et al.
      Determinants and outcomes of physical activity in patients with COPD: a systematic review.
      ], hence it may be important to explore the performance of the IPAQ-sf in these specific subgroups.
      This study aimed to assess the test-retest reliability/agreement and construct validity of the IPAQ-sf in people with COPD. A secondary aim of this study was to explore potential differences in the validity of the tool among groups of age, sex, and COPD levels of airflow obstruction.

      2. Methods

      2.1 Study design

      This was a cross-sectional study which was part of a larger study (ref. POCI-01-0145-FEDER-028446; PTDC/SAU-SER/28446/2017). Construct validity of the IPAQ-sf was assessed using accelerometer-based data. Test-retest reliability/agreement was calculated using the IPAQ-sf results obtained in two different occasions separated by 7 days, corresponding to the time participants used the accelerometer.

      2.2 Ethical considerations

      Ethical approval was obtained prior to study commencement from the Health Units participating in this study. Participants received verbal and written information about the study and provided written informed consent before data collection.

      2.3 Sample size

      Sample size was defined according to the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) guidelines [
      • Mokkink Lidwine B.
      • et al.
      COSMIN Methodology for Systematic Reviews of Patient-Reported Outcome Measures.
      ,
      • Terwee C.B.
      • et al.
      Qualitative attributes and measurement properties of physical activity questionnaires: a checklist.
      ], which recommend that a minimum of 50 individuals should be recruited to ensure the quality of studies assessing the measurement properties of instruments.

      2.4 Participants

      Patients with COPD were identified by physicians of the Leiria Hospital Centre, Baixo Vouga Hospital Centre, University Hospital Centre North Lisbon and a primary care centre (USF Santiago Marrazes), who ensured the fulfilment of the eligibility criteria. Patients included in the study had to be: 18 years old or more; diagnosed with COPD according to the GOLD criteria [
      Global strategy for the diagnosis management and prevention of COPD, Global Initiative for Chronic Obstructive Lung Disease (GOLD).
      ]; clinically stable in the previous month (i.e., no hospital admissions or acute exacerbations); able to understand Portuguese and to provide informed consent. Exclusion criteria consisted of the presence of severe neurologic (e.g., Parkinson, stroke), musculoskeletal (e.g., severe osteoarthritis) or psychiatric disorders (e.g., schizophrenia), unstable cardiovascular disease, or other health condition/impairment (e.g., severe visual or hearing impairment) that could preclude patients from understanding the study and/or participating in data collection. Data were collected at the Centre for Innovative Care and Health Technology (ciTechCare) of the Polytechnic of Leiria, at the Respiratory Research and Rehabilitation Laboratory – School of Health Sciences, University of Aveiro (Lab3R-ESSUA), or at the health units, depending on patients' and services’ availability.

      2.5 Data collection

      Participants completed a structured questionnaire with sociodemographic (age, sex, education level and work status) and general clinical information such as smoking status (never, current or former smokers), dyspnoea perception (modified Medical Research Council dyspnoea scale [mMRC] [
      • Doherty D.E.
      • et al.
      Chronic obstructive pulmonary disease: consensus recommendations for early diagnosis and treatment.
      ]) and presence of comorbidities (Charlson Comorbidity Index [CCI] [
      • Charlson M.E.
      • et al.
      A new method of classifying prognostic comorbidity in longitudinal studies: development and validation.
      ]) to characterise the sample. Comorbidities were classified as mild (CCI scores of 1–2), moderate (CCI scores of 3–4) or severe (CCI scores ≥5) [
      • Charlson M.E.
      • et al.
      A new method of classifying prognostic comorbidity in longitudinal studies: development and validation.
      ]. Height and weight were collected to calculate the body mass index (BMI). Lung function was assessed according to standardised guidelines [
      • Miller M.R.
      • et al.
      Standardisation of spirometry.
      ] with a portable spirometer (MicroLoop, CareFusion, Kent, UK) to characterise airflow obstruction limitation [
      Global strategy for the diagnosis management and prevention of COPD, Global Initiative for Chronic Obstructive Lung Disease (GOLD).
      ]: GOLD grades 1–4 (considering patients’ Forced Expiratory Volume in first second percentage predicted [FEV1% predicted]: GOLD 1 – FEV1 ≥ 80%; GOLD 2–50 ≤ FEV1 ≤ 79%; GOLD 3–30 ≤ FEV1 ≤ 49% and GOLD 4 – FEV1 <30%). All patients were advised to take their usual medication before data collection.
      Then, participants completed the IPAQ-sf (IPAQ-sf 1) and received an accelerometer (ActiGraph GT3X+, Pensacola, FL) to use for 7 days [
      • Rabinovich R.A.
      • et al.
      Validity of physical activity monitors during daily life in patients with COPD.
      ]. Patients were instructed to wear the accelerometer at the waist, on the dominant side, during waking hours, except for bathing or swimming. A second appointment was scheduled 8 days after the first appointment to retrieve the accelerometers and complete the IPAQ-sf once more (IPAQ-sf 2), for further assessment of test-retest reliability and agreement of the tool.

      2.6 Measures

      2.6.1 International physical activity questionnaire short-form (IPAQ-sf)

      The IPAQ-sf is composed of 7 questions, simple to administer in clinical practice, and provides information on the number of days/week and average time/day spent walking, in moderate- and vigorous-intensity activities and sitting, based on the previous 7 days, to further calculate energy expenditure in metabolic equivalents (METs) [
      • Craig C.L.
      • et al.
      International physical activity questionnaire: 12-country reliability and validity.
      ]. The continuous score of the IPAQ-sf can be calculated as “MET level ×minutesofactivityperday×daysperweek and is expressed in METs-min/week. It can be calculated for walking (3.3 METs), MPA (4 METs) and VPA (8 METs). The categorical score of the IPAQ-sf classifies a patients’ PA level as “low”, “moderate” or “high” [
      IPAQ
      Guidelines for the Data Processing and Analysis of the International Physical Activity Questionnaire.
      ]. These classifications can be then translated to “physically active” (corresponding to “moderate” or “high” PA levels) and “physically inactive” (which corresponds to “low” PA level) (Table 1). The Portuguese version of IPAQ-sf was used in this study [
      • Craig C.L.
      • et al.
      International physical activity questionnaire: 12-country reliability and validity.
      ] and it takes about 10 min to complete. The questionnaire is free of charge and can be found in the IPAQ website (https://sites.google.com/site/theipaq/home), along with a detailed scoring information.
      Table 1Categories of “physically active” and “physically inactive” obtained with the IPAQ-sf and accelerometer-based data.
      CategoryPhysically activePhysically inactive
      IPAQ-sfCorrespond to “high” and “moderate” scores of the IPAQ-sf:Correspond to “low” score of the IPAQ-sf:
      “High PA level”“Low PA level”
      a) vigorous-intensity PA on ≥ 3 days achieving ≥1500 MET-min/weeka) No PA is reported
      OROR
      b) 7 days of any combination of walking, moderate- or vigorous-intensity PA achieving ≥3000 MET-min/weekb) Some PA is reported but not enough to meet categories “high” or “moderate”
      “Moderate PA level”
      a) ≥ 3 days of vigorous-intensity PA of ≥20 min/day
      OR
      b) ≥ 5 days of moderate-intensity PA and/or walking of ≥30 min/day
      OR
      c) ≥ 5 days of any combination of walking, moderate- or vigorous-intensity PA achieving ≥600 MET-min/week
      Accelerometer (intensity-based approach) [
      • Garber C.E.
      • et al.
      American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise.
      ]
      a) ≥ 20 min/day of vigorous-intensity PA on ≥ 3 days, to reach a total of at least 75 min/weeka) No PA is reported
      OROR
      b) ≥ 30 min/day of moderate-intensity PA on ≥ 5 days, to reach a total of at least 150 min/weekb) Some PA is reported but not enough to meet the guidelines
      OR
      c) a combination of both
      Accelerometer (step-based approach) [
      • Garber C.E.
      • et al.
      American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise.
      ]
      a) ≥ 7000 steps/daya) Not achieving the minimum of 7000 steps/day
      Legend: IPAQ-sf, International Physical Activity Questionnaire - short form; METs, metabolic equivalent; PA, physical activity.

      2.6.2 Accelerometry

      Accelerometry was used as a criterion measure to validate the IPAQ-sf, similarly to other validation studies [
      • Ahn G.E.
      • et al.
      Self-reported and objectively measured physical activity in adults with systemic lupus erythematosus.
      ,
      • Marshall A.L.
      • et al.
      Reliability and validity of a brief physical activity assessment for use by family doctors.
      ,
      • Puig-Ribera A.
      • et al.
      Screening physical activity in family practice: validity of the Spanish version of a brief physical activity questionnaire.
      ,
      • Wanner M.
      • et al.
      Validation of the long international physical activity questionnaire: influence of age and language region.
      ]. In this study, the triaxial accelerometer ActiGraph GT3X+ was used, which has been validated in the COPD population [
      • Rabinovich R.A.
      • et al.
      Validity of physical activity monitors during daily life in patients with COPD.
      ,
      • Van Remoortel H.
      • et al.
      Validity of activity monitors in health and chronic disease: a systematic review.
      ]. The device collects and stores PA data which can be downloaded and converted into time-stamped PA counts and step counts using specific software (ActiLife 6, version 6.13.3, Pensacola, FL). A valid day was defined as a minimum of 8 h of wearing time [
      • Demeyer H.
      • et al.
      Standardizing the analysis of physical activity in patients with copd following a pulmonary rehabilitation program.
      ]. Patients who had less than 5 days of valid data from the 7-day wear interval were excluded, since 4 days are the minimum number of days needed for an accurate assessment of patients’ PA using accelerometers [
      • Demeyer H.
      • et al.
      Standardizing the analysis of physical activity in patients with copd following a pulmonary rehabilitation program.
      ], and at least 5 days are required to assess whether patients are physically active or not (considering the moderate-intensity PA – Table 1) [
      • Garber C.E.
      • et al.
      American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise.
      ]. Accelerometer-based data were then downloaded and analysed using the algorithms of Freedson (1998) [
      • Freedson P.S.
      • Melanson E.
      • Sirard J.
      Calibration of the computer science and applications, inc. accelerometer.
      ] with 60-s epoch, incorporated in the Actilife software: daily time (in min) spent in light-intensity PA (100–1951 counts-per-minute [CPM]), MPA (1952–5724 CPM), VPA (≥5725 CPM), and a combination of both (MVPA) [
      • Freedson P.S.
      • Melanson E.
      • Sirard J.
      Calibration of the computer science and applications, inc. accelerometer.
      ]. Data were retrieved in min/week to facilitate the comparison with the results from IPAQ-sf. The number of steps per day and per week was also collected. Participants were classified as “physically active” or “physically inactive” using two approaches, an intensity-based approach and a step-based approach, according to the American College of Sports Medicine (ACSM) guidelines [
      • Garber C.E.
      • et al.
      American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise.
      ] and World Health Organisation (WHO) [] (Table 1).

      2.7 Data analysis

      Descriptive statistics were used to characterise the sample regarding age, sex, FEV1% predicted, BMI, education level, work status, smoking status, GOLD airflow obstruction limitation (1–4), dyspnoea (mMRC), comorbidities (CCI) and PA results (IPAQ-sf and accelerometer-based data).

      2.7.1 Reliability and agreement

      Test-retest reliability of the IPAQ-sf was assessed using: 1) continuous values of IPAQ-sf 1 and IPAQ-sf 2 (METs-min/week); and 2) categories of IPAQ-sf 1 and 2 (i.e., “low PA”, “moderate PA” and “high PA”; and “physically active” vs. “physically inactive”). According to the guidelines [
      • Terwee C.B.
      • et al.
      Qualitative attributes and measurement properties of physical activity questionnaires: a checklist.
      ,
      • Kottner J.
      • et al.
      Guidelines for reporting reliability and agreement studies (GRRAS) were proposed.
      ,
      • Prinsen C.A.C.
      • et al.
      COSMIN guideline for systematic reviews of patient-reported outcome measures.
      ], the following analyses were conducted:
      • 1)
        For continuous variables:
        • a.
          Reliability was assessed using ICC2,1 and its 95% CI [
          • Watson P.F.
          • Petrie A.
          Method agreement analysis: a review of correct methodology.
          ]. An ICC of at least 0.70 was considered as a minimum standard for good reliability [
          • Terwee C.B.
          Qualitative attributes and measurement properties of physical activity questionnaires.
          ].
        • b.
          Agreement was calculated using the standard error of measurement (SEM=SDdifferences2), minimal detectable change at the 95% confidence level (MDC95=SEM×2×1.96), and the Bland and Altman 95% limits of agreement (LoA) [
          • Bland M.J.
          • Altman D.G.
          Statistical methods for assessing agreement between two methods of clinical measurement.
          ].
      • 2)
        For categorical variables:
        • a.
          Percentage of agreement was defined as the total number of participants assigned to the same category (either “physically active” or “physically inactive”) by both measures, divided by the total number of participants.
        • b.
          Cohen's weighted kappa coefficient and its 95% CI were used for ordinal variables (“low PA”, “moderate PA” and “high PA”) and Cohen's kappa for nominal variables (“physically inactive” and “physically active”). Results were interpreted as follows [
          • Landis G.K.J.
          The measurement of observer agreement for categorical data.
          ]: slight (≤0.20), fair (0.21–0.40), moderate (0.41–0.60), substantial (0.61–0.80) and almost perfect (0.81–1.00). An acceptable value of kappa was considered as ≥ 0.70 [
          • Terwee C.B.
          Qualitative attributes and measurement properties of physical activity questionnaires.
          ].

      2.7.2 Construct validity

      The IPAQ-sf 2 and accelerometer-based data were used to assess the construct validity of the PA assessment tool, since they referred to the same period. Criterion validity was not possible to assess as there is still no gold standard for the assessment of daily PA [
      • Terwee C.B.
      • et al.
      Qualitative attributes and measurement properties of physical activity questionnaires: a checklist.
      ,
      • Sattler M.C.
      • et al.
      Current evidence of measurement properties of physical activity questionnaires for older adults: an updated systematic review.
      ].
      The variables used from IPAQ-sf were the following (all in min/week): METs-min/week, time spent in VPA (i.e., product of IPAQ-sf questions 1 and 2), time spent in MPA (i.e., product of IPAQ-sf questions 3 and 4) and in time spent in walking (i.e., product of IPAQ-sf questions 5 and 6). From accelerometry, the following variables were used: time spent in VPA, MPA and MVPA (combination between VPA and MPA) (in min/week), and step counts per week. The question regarding the time spent sitting (Q7) is not included as part of the continuous score and was not addressed in the present study. Normality of data distribution was assessed using the Kolmogorov-Smirnov test for each variable. The following analyses were conducted, according to the guidelines [
      • Kottner J.
      • et al.
      Guidelines for reporting reliability and agreement studies (GRRAS) were proposed.
      ]:
      • 1)
        For continuous variables:
        • a.
          Spearman's rank-order correlations (ρ) or Pearson's correlation coefficient (r) (according to the [non-]normality of data distribution) were used in the total sample and in the following subgroups: 1) age (<65 and ≥65 years old); 2) sex (male and female); and 3) GOLD airflow obstruction levels (GOLD 1, 2, 3 and 4). Construct validity is often considered good if correlations are positive, significant and ≥0.50 [
          • Terwee C.B.
          Qualitative attributes and measurement properties of physical activity questionnaires.
          ]. Strength of the correlations were based on criteria from Evans [
          • Evans J.D.
          Straightforward Statistics for the Behavioral Sciences.
          ]: very weak (0.00–0.19), weak (0.20–0.39), moderate (0.40–0.59), strong (0.60–0.79) and very strong (0.80–1.0).
        • b.
          Bland and Altman's 95% LoA were used to compare the two measurement methods on variables that have used same units: weekly time spent on vigorous activity (VPA), moderate activity (MPA) and walking.
      • 2)
        For categorical variables:
        • a.
          The ability of the IPAQ-sf for classifying “physically active” and “physically inactive” patients was evaluated against the accelerometer-based data, using the cut-off points previously described (Table 1). Percentage of agreement and Cohen's kappa coefficient were used.
        • b.
          Sensitivity (i.e., those who were correctly classified as “physically active” by the IPAQ-sf using the accelerometer-based data) and specificity (i.e., those who were correctly classified as “physically inactive” by the IPAQ-sf using the same criteria) were also calculated, including the 95% CI. The 95% CI were calculated for sensitivity and specificity using the following formula =p±1.96p(1p)n, where “p” is the relevant proportion (i.e., sensitivity or specificity) and “n” is the total sample [
          • Watson P.F.
          • Petrie A.
          Method agreement analysis: a review of correct methodology.
          ].
        • c.
          Positive and negative predictive values (PPV and NPV, respectively) were calculated and refer to the proportion of “physically active” (PPV) and “physically inactive” (NPV) participants classified by the IPAQ-sf who were “truly physically active” and “truly physically inactive”, respectively, having the accelerometer as the reference standard.
      All data were analysed using SPSS version 24 (IBM Corp., Armonk, USA) and GraphPad Prism Version 8.0.1. (263). Statistical significance was set at p < 0.05.

      3. Results

      3.1 Participants

      A total of 103 patients with COPD were identified. From these, 18 refused to participate, 2 withdrew from participating and 1 died. Additionally, 2 reported having had an exacerbation in the previous days and 7 were not available to participate at the moment of data collection. When considering the IPAQ scoring guidelines [
      IPAQ Research Committee
      Guidelines for data processing and analysis of the international physical activity questionnaire (IPAQ) – short and long form.
      ] eleven participants were excluded from the analysis due to: presenting a very high score, i.e., >16 h at walking, moderate and vigorous PA (n = 3); being significative outliers, i.e., ≥16 h of different intensities PA (n = 3) and missing data (n = 5; 2 in the IPAQ-sf and 3 in accelerometry). The final sample was composed of 62 participants.
      Participants had a mean (± standard deviation) age of 68 ± 8 years old and 53 (86%) participants were male. They were slightly overweight (BMI = 27 ± 5 kg/m2) and presented a FEV1 of 51 ± 23% predicted. Their detailed sociodemographic and clinical characteristics are presented in Table 2. Most participants were in GOLD 2 (n = 25, 40%) and GOLD 3 (n = 20, 32%) of airflow obstruction. All participants reported comorbidities, the most common being arterial hypertension (n = 26, 43%), dyslipidemia (n = 18, 30%) and mental health problems, such as anxiety and depression (n = 23, 43%).
      Table 2Participants’ sociodemographic and clinical characteristics (n = 62).
      Participants' characteristics (n = 62)
      Age (years), mean (SD)68 (8)
      Sex (male), n (%)53 (86%)
      FEV1% predicted, mean (SD)51 (23)
      BMI (kg/m2), mean (SD)27 (5)
      Education Level, n (%)
       No qualifications2 (3%)
       1st cycle (years 1–4)26 (42%)
       2nd cycle (years 5–6)7 (11%)
       3rd cycle (years 7–9)7 (11%)
       High school (years 10–12)14 (23%)
       University6 (10%)
      Work status, n (%)
       Retired50 (82%)
       Full/part-time employment5 (8%)
       Unemployed (health-related reason)5 (8%)
      Smoking status, n (%)1
       Never8 (14%)
       Current smokers11 (19%)
       Former smokers39 (68%)
      GOLD airflow obstruction levels, n (%)
       GOLD 15 (8%)
       GOLD 225 (40%)
       GOLD 320 (32%)
       GOLD 412 (19%)
      mMRC, median [Q1; Q3]2 [1; 2]
      CCI, n (%)
       Mild8 (13%)
       Moderate43 (71%)
       Severe10 (16%)
      Legend: BMI, body mass index; CCI, Charlson comorbidity index; FEV1, forced expiratory volume in first second; FVC, forced vital capacity; mMRC, Modified Medical Research Council; SD, standard deviation. Q, quartile. 1Missing cases: 4.

      3.2 Physical activity levels

      Physical activity data are presented in Table 3. None of the variables from the IPAQ-sf or the accelerometer followed a normal distribution, hence data are presented as median (quartile [Q]1; Q3). More than 50% of the sample did not meet the international PA recommendations (median of MPA = 85 min/week), which is lower than the 150 min/week recommended [
      • Garber C.E.
      • et al.
      American College of Sports Medicine position stand. Quantity and quality of exercise for developing and maintaining cardiorespiratory, musculoskeletal, and neuromotor fitness in apparently healthy adults: guidance for prescribing exercise.
      ]. From 62 participants, 56 used the accelerometer for 7 days (4 used for 6 days and 2 used for 5 days).
      Table 3Data from the IPAQ-sf, IPAQ-sf 2 (retest) and accelerometer-based data (n = 62).
      IPAQ-sf 1 (min/week)
       Total energy expenditure (METs-min/week)1193 [220; 2996]
       Time in moderate PA60 [0; 285]
       Time in vigorous PA0 [0; 0]
       Time in walking130 [0; 300]
      IPAQ-sf 2, median (min/week)
       Total energy expenditure (METs-min/week)1550 [309; 3254]
       Time in moderate PA73 [0; 304]
       Time in vigorous PA0 [0; 180]
       Time in walking140 [28; 360]
      Accelerometry (min/week)
       Time in moderate PA85 [46; 248]
       Time in vigorous PA1 [1; 2]
       Total time in MVPA87 [47; 248]
       Steps (per day)3504 [2313; 5766]
      Legend: IPAQ-sf, International Physical Activity Questionnaire-short form; METs, metabolic equivalent; Min, minutes; MVPA, moderate and vigorous physical activity; PA, physical activity; SD, standard deviation. The results are presented in median (the percentile 25 [Q1]; percentile 75 [Q3]).

      3.3 Test-retest reliability and agreement of IPAQ-sf

      3.3.1 IPAQ-sf continuous scores

      Test-retest reliability and agreement of the IPAQ-sf were first analysed using the continuous scores from IPAQ-sf 1 and 2 (in METs-min/week). The ICC was 0.707 (95% CI 0.515–0.823), and the values of the SEM and MDC95 were 1840 METs-min/week and 4971 METs-min/week, respectively.
      Fig. 1 presents a Bland and Altman plot with the 95% LoA between the IPAQ-sf 1 and 2 (METS-min/week). A bias (i.e., mean differences between IPAQ-sf 1 and 2) of −18.6 METs-min/week (standard deviation of bias = 3279 METs-min/week) was observed, with wide 95% LoA ranging from −6446 to 6409 METs-min/week, and no evidence of consistent bias was found.
      Fig. 1
      Fig. 1Bland and Altman plots between IPAQ-sf 1 e 2 (total METs-min/week) in patients with chronic obstructive pulmonary disease (n = 62).

      3.3.2 IPAQ-sf categories

      The percentage of agreement among IPAQ-sf categories (“low PA”, “moderate PA” and “high PA”) obtained from IPAQ-sf 1 and 2 was 66% and the weighted Cohen's kappa was 0.496 (95% CI 0.329–0.663), as shown in appendix A. When considering the categories “physically inactive” (i.e., low PA) and “physically active” (i.e., moderate to high PA), the agreement was 84% and the Cohen's kappa was 0.660 (95% CI 0.493–0.827), as shown in Table 4.
      Table 4Percentage of agreement and weighted Cohen's kappa among IPAQ-sf categories (“physically inactive” and “physically active”) (n = 62).
      IPAQ-sf 2% AgreementKappa (95% CI)
      Physically InactivePhysically Active
      IPAQ-sf 1Physically Inactive19684%0.660 (0.493–0.827)
      Physically Active433
      Legend: CI, confidence intervals; IPAQ-sf, International Physical Activity Questionnaire-short form.

      3.4 Validity of the IPAQ-sf

      3.4.1 IPAQ-sf and accelerometry - continuous variables

      Correlations between measurement methods were positive, moderate and significant in all PA variables (0.396 ≤ ρ ≤ 0.527, p < 0.001), except for VPA (ρ = 0.006 p > 0.05) (appendix B). Overall, the IPAQ-sf overestimated the weekly time spent in activity (mean differences between methods [95% LoA] for VPA = 45 min/week [135–224], MPA = 18 min/week [−480 – 515] and Walking = 35 min/week, [−491 – 561] and this was more evident the longer the patients report being active, particularly in VPA (Figures 2, 3 and 4).

      3.4.2 Subgroup analyses

      Significant, positive and moderate correlations were found between the IPAQ-sf and accelerometry in patients independently of the age group and in male patients (except for VPA in both groups, p > 0.05). The highest values were obtained in patients with <65 years (0.467 ≤ ρ ≤ 0.651, p < 0.05) and in male patients (0.466 ≤ ρ ≤ 0.653, p < 0.001). Correlations were negative and non-significant for female patients (−0.594 ≤ ρ ≤ −0.159, p > 0.05). In GOLD grades, significant correlations were only found for: IPAQ-sf total score and total duration in MVPA (accelerometry) (GOLD 2 and 4), time in MPA (GOLD 2), time in walking and in MPA (GOLD 4), and time in walking and steps per week (GOLD 1 and 4) (p < 0.05). All correlations can be found in appendix C.

      3.4.3 IPAQ-sf and accelerometry - categorical variables

      The agreement between instruments to identify “physically active” or “physically inactive” participants was 65% and Cohen's kappa was 0.313 (95% CI 0.146–0.480) (Table 5). The sensitivity and specificity of IPAQ-sf 2 were 0.830 (95% CI 0.739–0.921) and 0.500 (95% CI 0.380–0.621), respectively. PPV and NPV were 0.564 (95% CI 0.503–0.625) and 0.783 (95% CI 0.731–0.833), respectively (Table 5).
      Table 5Comparison of the activity categories (“physically active” and “physically inactive”) obtained from the IPAQ-sf 2 and accelerometer-based data (n = 62).
      Accelerometer% agreementKappa (95% CI)Sensitivity (95% CI)Specificity (95% CI)PPV (95% CI)NPV (95% CI)
      Physically InactivePhysically Active
      IPAQ-sf 2Physically Inactive18565%0.313 (0.146–0.480)0.830 (0.739–0.921)0.500 (0.380–0.621)0.564 (0.503–0.625)0.783 (0.731–0.833)
      Physically Active1722
      Legend: CI, confidence intervals; IPAQ-sf, International Physical Activity Questionnaire-short form; NPV, Negative predictive value; PPV, Positive predictive value.

      4. Discussion

      The present study suggests that the IPAQ-sf is valid to be used in patients with COPD and has good test-retest reliability but with wide limits of agreement which may limit the accuracy of this instrument. When stratifying patients by age, sex and GOLD airflow obstruction levels, the highest correlations were found in patients with <65 years and in male patients.
      These findings show that the IPAQ-sf may not be a reliable measure, nevertheless, patients may have also increased awareness of their PA levels by wearing the accelerometer [
      • Blikman T.
      • et al.
      Reliability and validity of the Dutch version of the International Physical Activity Questionnaire in patients after total hip arthroplasty or total knee arthroplasty.
      ,
      • Wendel-Vos G.C.
      • et al.
      Reproducibility and relative validity of the short questionnaire to assess health-enhancing physical activity.
      ]. Similar results have been reported in other studies assessing the test-retest reliability of IPAQ-sf in several populations [
      • Craig C.L.
      • et al.
      International physical activity questionnaire: 12-country reliability and validity.
      ,
      • Cruz J.
      • Jácome C.
      • Marques A.
      Is the international physical activity questionnaire (IPAQ-sf) valid to assess physical activity in patients with COPD? Comparison with accelerometer data.
      ,
      • Faulkner G.
      • Cohn T.
      • Remington G.
      Validation of a physical activity assessment tool for individuals with schizophrenia.
      ]. Results from the present study were, in general, more positive than the results from a previous exploratory study conducted in COPD [
      • Cruz J.
      • Jácome C.
      • Marques A.
      Is the international physical activity questionnaire (IPAQ-sf) valid to assess physical activity in patients with COPD? Comparison with accelerometer data.
      ], which revealed a lower ICC in test-retest reliability (ICC = 0.439, 95% CI -0.267—0.838) and even wider limits of agreement (−10361—4548 METs-min/week).
      This study showed that, when considering the test-retest agreement using the LoA, the standard deviation of the bias of the IPAQ-sf (3279 MET-min/week) was higher than the IPAQ-sf cut-off scores for categorising individuals as “physically active” (i.e., at least 600 MET-min/week) [
      IPAQ
      Guidelines for the Data Processing and Analysis of the International Physical Activity Questionnaire.
      ]. A similar finding was observed in the MDC95 (4971 METs-min/week). When analysing the IPAQ-sf categories “physically active” and “physically inactive”, the percentage of agreement was higher than when the categories “high PA level”, “moderate PA level” and “low PA level” were considered (84% vs. 66%, respectively), and above the recommended standard for reliability coefficients [
      • Terwee C.B.
      • et al.
      Qualitative attributes and measurement properties of physical activity questionnaires: a checklist.
      ]. This can be justified by the fact that the category “physically active” includes both “high PA level” and “moderate PA level”. LoA (or the MDC95) can be considered “true” changes after an intervention [
      • Terwee C.B.
      • et al.
      Qualitative attributes and measurement properties of physical activity questionnaires: a checklist.
      ], and the LoA were wide (i.e., higher than the IPAQ-sf cut-off scores for categorising individuals as “physically active” - at least 600 MET-min/week), the IPAQ-sf may not be appropriate to assess patients' PA levels throughout time. This was somewhat expected since the IPAQ-sf questionnaire was originally designed for PA surveillance studies [
      • Craig C.L.
      • et al.
      International physical activity questionnaire: 12-country reliability and validity.
      ] and not for assessing PA changes or the impact of interventions on individuals' PA levels. Thus, caution is needed when using the IPAQ-sf to register patients’ PA evolution/progression in PA levels in clinical practice to avoid imprecise assessment which may interfere with the tailored intervention.
      The Stanford Seven-Day Physical Activity Recall (PAR), which was previously tested for construct validity in patients with COPD using accelerometry, showed similar results to the ones provided in the present study (r = 0.54, p < 0.001) [
      • Garfield B.E.
      • et al.
      Stanford seven-day physical activity recall questionnaire in COPD.
      ]. When comparing the IPAQ-sf to the Clinical Visit PROactive tool [
      • Gimeno-Santos E.
      • et al.
      The PROactive instruments to measure physical activity in patients with chronic obstructive pulmonary disease.
      ], this instrument presented slightly higher correlations with related constructs (r > 0.6) and higher test-retest reliability (ICC≥0.9). However, the PROactive tool is a hybrid tool (i.e., combines a short patient-reported outcome questionnaire and an activity monitor), which makes it less feasible to be used in clinical settings with low resources. Therefore IPAQ-sf seems to be an applicable questionnaire to assess PA in patients with COPD since the correlations were higher than the threshold recommended [
      • Terwee C.B.
      Qualitative attributes and measurement properties of physical activity questionnaires.
      ] in most variables and presented similar results compared to more complex instruments [
      • Copeland J.L.
      • Esliger D.W.
      Accelerometer assessment of physical activity in active, healthy older adults.
      ,
      • Swartz A.M.
      • et al.
      Estimation of energy expenditure using CSA accelerometers at hip and wrist sites.
      ]. Nevertheless, no significant correlations were found in VPA measured with the two instruments. This is somewhat expected as few patients engage in vigorous-intensity PA and its duration is normally limited [
      • Hartman J.E.
      • et al.
      Physical Activity Recommendations in Patients with Chronic Obstructive Pulmonary Disease.
      ]; and IPAQ-sf may overestimate time spent in VPA in this population. The exploratory study carried out in patients with COPD [
      • Cruz J.
      • Jácome C.
      • Marques A.
      Is the international physical activity questionnaire (IPAQ-sf) valid to assess physical activity in patients with COPD? Comparison with accelerometer data.
      ] revealed a higher correlation between IPAQ-sf and accelerometry than in the present study (r = 0.729, p = 0.017). The bigger sample size of the present study may justify the differences found between studies and suggests that larger studies should be carried out in this population to ensure more robust results.
      In clinical practice, an accurate tool for assessing PA levels and identifying physically inactive patients is crucial to enable healthcare professionals to provide adequate advice. The IPAQ-sf may be useful for this purpose in COPD but caution is required, since it has high sensitivity but a low specificity (0.830 and 0.500, respectively), which means that the IPAQ-sf may wrongly classify individuals as “active” when they are actually “truly inactive” (low specificity, i.e., a high number of false positives having the accelerometer as the reference standard). These results are in line with a previous study [
      • Hurtig-Wennlöf A.
      • Hagströmer M.
      • Olsson L.A.
      The International Physical Activity Questionnaire modified for the elderly: aspects of validity and feasibility.
      ], which has adapted and validated the IPAQ-sf to the elderly population (IPAQ-E). The authors found sensitivity results similar to the present study (81%) but higher specificity (85%), since it was an adapted version of IPAQ-sf. Future research should explore whether the IPAQ-E is more suitable for the COPD population, as most patients are older [
      • Raherison C.
      • Girodet P.O.
      Epidemiology of COPD.
      ]. To the best of the authors’ knowledge, previous studies on measurement properties of instruments for PA assessment in patients with COPD have not provided information of sensitivity and specificity. To overcome the uncertainty of classifying a “truly inactive patient” as “physically active” with the IPAQ-sf in clinical practice, the authors suggest healthcare professionals to confirm this categorisation through other methods, such as asking patients about PA routines or, if possible, perform an objective assessment using PA monitors.
      When stratifying patients by subgroups, correlations in the subgroup of ≥65 years were below the recommended threshold (ρ > 0.50), although significant; additionally, the strongest correlations were found in total METs-min/week in males (ρ = 0.653, p < 0.001) and <65 years (ρ = 0.651, p < 0.001), which is in line with the fact that IPAQ-sf was initially developed to people with <65 years [
      • Craig C.L.
      • et al.
      International physical activity questionnaire: 12-country reliability and validity.
      ] and, thus, it may not be adjusted to older people. The study of Hurting-Wennlöf's et al. [
      • Hurtig-Wennlöf A.
      • Hagströmer M.
      • Olsson L.A.
      The International Physical Activity Questionnaire modified for the elderly: aspects of validity and feasibility.
      ] presented a positive correlation between self-reported activity domains with the objectively assessed PA by an accelerometer (ρ = 0.277–0.471), but with a systematic error observed.
      Although the IPAQ-sf is widely used in several populations [
      • Lee P.H.
      • et al.
      Validity of the international physical activity questionnaire short form (IPAQ-SF): a systematic review.
      ,
      • Tierney M.
      • Fraser A.
      • Kennedy N.
      Criterion validity of the international physical activity questionnaire short form (IPAQ-SF) for use in patients with rheumatoid arthritis: comparison with the SenseWear armband.
      ,
      • Kaleth A.S.
      • et al.
      Validity and reliability of community health activities model program for seniors and short-form international physical activity questionnaire as physical activity assessment tools in patients with fibromyalgia.
      ,
      • Ahn G.E.
      • et al.
      Self-reported and objectively measured physical activity in adults with systemic lupus erythematosus.
      ], this study highlights that caution should be taken when using it as an isolated indicator of PA in COPD [
      • Lee P.H.
      • et al.
      Validity of the international physical activity questionnaire short form (IPAQ-SF): a systematic review.
      ].

      4.1 Limitations and future work

      This study has some limitations that need to be acknowledged. The IPAQ-sf was designed to be used by adults aged 18–65 years [
      • Craig C.L.
      • et al.
      International physical activity questionnaire: 12-country reliability and validity.
      ] and, in this study, participants had a mean (±SD) age higher than that range (68 ± 8 years) which may have had influenced the results. Additionally, the original authors of the IPAQ-sf [
      • Craig C.L.
      • et al.
      International physical activity questionnaire: 12-country reliability and validity.
      ] recommended the “last 7 days recall” version of IPAQ-sf for studies assessing PA. However, the last 7 days may not represent the usual pattern of patients’ weekly PA, which is dependent of several factors, such as weather conditions [
      • Chan C.B.
      • Ryan D.A.
      Assessing the effects of weather conditions on physical activity participation using objective measures.
      ]. Further studies should explore the “usual week” IPAQ-sf to understand if the correlations remain consistent. Nevertheless, there was only a small percentage (10%) of patients who had less than 7 valid days of PA monitoring. Another limitation concerns to the use of accelerometers as the comparator (gold standard). Although they are valid to assess PA of patients with COPD [
      • Rabinovich R.A.
      • et al.
      Validity of physical activity monitors during daily life in patients with COPD.
      ,
      • Van Remoortel H.
      • et al.
      Validity of activity monitors in health and chronic disease: a systematic review.
      ], some activities such as water-based activities and movement of the upper limbs cannot be assessed [
      • Lee I.M.
      • Shiroma E.J.
      Using accelerometers to measure physical activity in large-scale epidemiological studies: issues and challenges.
      ]. This study was conducted with stable patients with COPD hence, generalisability of results to other states of COPD and/or to other diseases is not possible. In addition, most participants in this sample were male. In female patients, no significant correlations were found between the IPAQ-sf 2 and any of the PA variables obtained through accelerometry. This could be justified by the lower sample size in the female subgroup (n = 9). In addition, there was some variability in the correlation results in the different GOLD grades. This finding may be partially explained by the unbalanced sample sizes in the groups, but it may also indicate that the IPAQ-sf is not an adequate tool for assessing PA levels in different airflow obstruction levels of the disease. Further research with a larger, more balanced sample of female patients and patients in the different GOLD groups and different countries, as well as longitudinal studies, are needed to reenforce these findings and to ensure external validity of findings.

      5. Conclusions

      Findings from this study showed that the IPAQ-sf presents positive and significant correlations with accelerometry, as well as high test-retest reliability but with large 95% limits of agreement, suggesting that the IPAQ-sf may not be appropriate to assess patients' PA levels throughout time. This was somehow expected since the IPAQ-sf questionnaire was originally designed for PA surveillance studies and not for assessing PA changes or the impact of interventions on individuals’ PA levels.

      Funding

      This work was funded by FEDER - Fundo Europeu de Desenvolvimento Regional by COMPETE 2020 – Programa Operacional Competitividade e Internacionalização (POCI) and national funds by Fundação para a Ciência e a Tecnologia (FCT), under the “OnTRACK project - Time to Rethink Activity Knowledge: a personalized mHealth coaching platform to tackle physical inactivity in COPD” (POCI-01-0145-FEDER-028446, PTDC/SAU-SER/28446/2017); national funds by FCT (UIDB/05704/2020, UIDP/05704/2020, UIDB/04501/2020). SF and NH were financially supported by PhD fellowships DFA/BD/6954/2020 and 2021.05188.BD, respectively, funded by FCT/MCTES, FSE, Por_Centro and UE.

      CRediT authorship contribution statement

      Sofia Flora: Methodology, Formal analysis, Investigation, Writing – original draft, Visualization. Alda Marques: Conceptualization, Writing – review & editing, Supervision. Nádia Hipólito: Investigation, Writing – review & editing. Nuno Morais: Validation, Formal analysis, Resources, Writing – review & editing, Supervision. Cândida G. Silva: Validation, Formal analysis, Resources, Writing – review & editing, Supervision. Filipa Januário: Writing – review & editing, Supervision. Fátima Rodrigues: Writing – review & editing, Supervision. Bruno P. Carreira: Writing – review & editing, Supervision. J. Cruz: Conceptualization, Methodology, Validation, Formal analysis, Resources, Writing – review & editing, Visualization, Supervision, Project administration.

      Declaration of competing interest

      None.

      Appendix A. Supplementary data

      The following is the supplementary data to this article:

      Appendix A. Percentage of agreement and weighted Cohen's kappa among IPAQ-sf categories (“low PA”, “moderate PA” and “high PA”) (n = 62)

      Tabled 1
      IPAQ-sf 2% agreementKappa (95% CI)
      Low PAModerate PAHigh PA
      IPAQ-sf 1Low PA192466%0.496 (0.329–0.663)
      Moderate PA4139
      High PA029
      Legend: CI, confidence intervals; IPAQ-sf, International Physical Activity Questionnaire-short form; PA, physical activity.

      Appendix B. Correlations (ρ) between IPAQ-sf 2 and accelerometry (n = 62)

      Tabled 1
      SourceCorrelations (min/week)ρ
      IPAQ-sfTotal METs-min/week0.527**
      AccelerometryTime in MVPA
      IPAQ-sfTime in VPA0.006
      AccelerometryTime in VPA
      IPAQ-sfTime in MPA0.444**
      AccelerometryTime in MPA
      IPAQ-sfTime in Walking0.396**
      AccelerometryTime in MPA
      IPAQ-sfTime in walking0.434**
      AccelerometryNumber of steps/week
      Legend: IPAQ-sf, International Physical Activity Questionnaire-short form; MPA, moderate physical activity; MVPA, moderate to vigorous physical activity; PA, physical activity; VPA, vigorous physical activity. *p < 0.05 **p < 0.001.

      Appendix C. Correlations (ρ) between IPAQ-sf 2 and accelerometer-based data stratified by age, sex and GOLD grades

      Tabled 1


      Source
      (min/week)AgeSexGOLD airflow obstruction levels
      65 years (n = 20)≥ 65 years (n = 42)Male (n = 53)Female (n = 9)GOLD 1 (n = 5)GOLD 2 (n = 25)GOLD 3 (n = 20)GOLD 4 (n = 12)
      IPAQ-sf 2Total METs-min0.651**0.443**0.653**−0.4500.3000.491**0.4370.635*
      ACTotal MVPA
      IPAQ-sf 2Time in VPA0.240−0.1520.092−0.3590.0570.242−0.3170.305
      ACTime in VPA
      IPAQ-sf 2Time in MPA0.517*0.393*0.524**−0.2940.0510.431*0.3520.541
      ACTime in MPA
      IPAQ-sf 2Time in Walking0.467*0.395**0.466**−0.1590.5640.1590.3120.640*
      ACTime in MPA
      IPAQ-sf 2Time in MPA and walking0.3770.444**0.507**−0.5940.975**0.2320.2820.707*
      ACNumber of steps/week
      Legend: AC, accelerometry; COPD, Chronic Obstructive Pulmonary Disease; IPAQ-sf, International Physical Activity Questionnaire-short form; MPA, moderate physical activity; MVPA, moderate to vigorous physical activity; PA, physical activity; VPA, vigorous physical activity. *p < 0.05 **p < 0.001.

      Appendix D. Bland and Altman plots (n = 62)

      Figures 2, 3 and 4 present a Bland and Altman plot with the 95% LoA between the IPAQ-sf 2 and accelerometery regarding VPA (mean differences (bias) = 45 min/week, SD of bias = 91 min/week, 95% LoA = −135 – 224 min/week), MPA (bias = 18 min/week, SD of bias = 254 min/week, 95% LoA = −480 – 515 min/week) and Walking (bias = 35 min/week, SD of bias = 268 min/week, 95% LoA = −491 – 561 min/week), respectively.
      Fig. 2
      Fig. 2Bland and Altman plots for vigorous physical activity (VPA) in patients with chronic obstructive pulmonary disease (n = 62). Comparison between IPAQ-sf 2 and accelerometry measurements (min/week).
      Fig. 3
      Fig. 3Bland and Altman plots for moderate physical activity (MPA) in patients with chronic obstructive pulmonary disease (n = 62). Comparison between IPAQ-sf 2 and accelerometry measurements (min/week).
      Fig. 4
      Fig. 4Bland and Altman plots for walking in patients with chronic obstructive pulmonary disease (n = 62). Comparison between IPAQ-sf 2 and accelerometry measurements (min/week).

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