Purpose: Cardiorespiratory fitness (CRF) plays an essential role in health outcomes and quality of life. However, it is often not assessed nor estimated. Objective CRF assessment is costly, labour intensive and not widely available. Patient-reported outcome measures estimate CRF more cost-efficiently, but current questionnaires lack accuracy. The aim of this study is to develop a new self-reported questionnaire to estimate CRF. Materials and Methods: The FitMáx©-questionnaire, consisting of only three questions assessing walking, stair climbing, and cycling capacity, was compared with the commonly used Duke Activity Status Index (DASI) and Veterans Specific Activity Questionnaire (VSAQ). These questionnaires were compared to peak oxygen uptake (VO_2peak) as measured with cardiopulmonary exercise testing. This study included 759 cardiac, pulmonary and oncologic patients and healthy persons aged 18‒90. Results: FitMáx© strongly correlated (r = 0.94 (0.92‒0.95) SEE = 4.14 mL∙kg^{− 1}∙min^{− 1}) with measured VO_2peak. Bias between predicted and measured VO_2peak was − 0.24 (− 9.23‒8.75; 95% limits of agreement) mL·kg^{− 1}·min^{− 1}. The FitMáx© scored superiorly on correlation and SEE compared with the DASI and VSAQ, r = 0.75 (0.68‒0.80) SEE = 4.62 mL∙kg^{− 1}∙min^{− 1} and r = 0.87 (0.83‒0.90) SEE = 6.75 mL∙kg^{− 1}∙min^{− 1}, respectively. Conclusion: FitMáx© is a valid and accessible questionnaire to estimate CRF expressed as VO_2peak in clinical practice and shows substantial improvement compared to currently used questionnaires.

Purpose: The FitMáx© was developed as a questionnaire-based instrument to estimate Cardiorespiratory Fitness (CRF) expressed as oxygen uptake at peak exercise (VO_2peak). Test–retest reliability is a clinometric measurement property, which defines stability over time if multiple measurements are performed (i.e. reliability). The present study aimed to assess the test–retest reliability of the FitMáx©-questionnaire in different patient groups. Patients and methods: A total of 127 cardiac, pulmonary and oncology patients and healthy subjects aged 19–84 years who completed the questionnaire twice within an average of 18 days were included for analysis. Participants were in a stable clinical situation (no acute disease or participating in a training program). To determine the test–retest reliability, the Intraclass Correlation Coefficient (ICC) and Standard Error of the Measurement (SEM) was calculated between the first (T₀) and second (T₁) administration of the questionnaires. Results: An excellent agreement was found between the FitMáx©-questionnaire scores at T₀ and T₁, with an ICC of 0.97 (SEM 1.91) in the total study population and an ICC ranging from 0.93 to 0.98 (SEM 1.52–2.27) in the individual patient groups. Conclusion: The FitMáx©-questionnaire proves to be reliable and stable over time to estimate CRF of patients and healthy subjects. Trial registration NTR (Netherlands Trial Register), NL8846. Registered 25 August 2020, https://trialsearch.who.int/Trial2.aspx?TrialID=NL8846

Background: Evaluating the criterion validity and responsiveness of the self-reported FitMáx©-questionnaire, Duke Activity Status Index (DASI) and Veterans Specific Activity Questionnaire (VSAQ) to monitor aerobic capacity in cancer survivors. Methods: Cancer survivors participating in a 10-week supervised exercise program were included. The FitMáx©-questionnaire, DASI, VSAQ and a cardiopulmonary exercise test (CPET) were completed before (T₀) and after (T₁) the program. Intraclass correlation coefficients (ICC) were calculated between VO_2peak estimated by the questionnaires (questionnaire-VO_2peak) and VO_2peak measured during CPET (CPET-VO_2peak), at T₀ to examine criterion validity, and between changes in questionnaire-VO_2peak and CPET-VO_2peak (ΔT₀-T₁) to determine responsiveness. Receiver operating characteristic (ROC) analyses were performed to examine the ability of the questionnaires to detect true improvements (≥ 6%) in CPET-VO_2peak. Results: Seventy participants were included. Outcomes at T₁ were available for 58 participants (83%). Mean CPET-VO_2peak significantly improved at T₁ (Δ1.6 mL·kg^− 1·min^− 1 or 8%). Agreement between questionnaire-VO_2peak and CPET-VO_2peak at T₀ was moderate for the FitMáx©-questionnaire (ICC = 0.69) and VSAQ (ICC = 0.53), and poor for DASI (ICC = 0.36). Poor agreement was found between ΔCPET-VO_2peak and Δquestionnaire-VO_2peak for all questionnaires (ICC 0.43, 0.19 and 0.18 for the FitMáx©-questionnaire, VSAQ and DASI, respectively). ROC analysis showed that the FitMáx©-questionnaire was able to detect improvements in CPET-VO_2peak (area under the curve, AUC = 0.77), when using a cut-off value of 1.0 mL·kg^− 1·min^− 1, while VSAQ (AUC = 0.66) and DASI (AUC = 0.64) could not. Conclusion: The self-reported FitMáx©-questionnaire has sufficient validity to estimate aerobic capacity in cancer survivors at group level. The responsiveness of the FitMáx©-questionnaire for absolute change is limited, but the questionnaire is able to detect whether aerobic capacity improved. The FitMáx©-questionnaire showed substantial better values of validity and responsiveness compared to DASI and VSAQ.

Peak oxygen uptake (VO_2peak), assessed by maximal cardiopulmonary exercise testing (CPET), is a powerful predictor of cardiovascular morbidity and mortality. In clinical practice, the use of CPET is often not feasible or desirable in (older) frail patients.¹ In the last decades, several exercise and non-exercise-based algorithms to predict VO_2peak were evaluated.² These prediction models are less accurate than CPET, yet easily accessible and applicable.³ Overall, reviews showed low to moderate correlation for non-exercise algorithms [r = 0.66–0.86, and SEE (standard error of estimate) 3.82–7.31 mL/kg/min] and submaximal exercise-based algorithms (r = 0.21–0.70, and SEE 2.50–4.43) in a healthy population.^2,4,5 However, elderly patients with chronic diseases were typically excluded in the development and validation of these models.⁶ The current study aimed to investigate the accuracy of two self-reported questionnaires to predict VO_2peak in chronic heart failure (CHF) patients; the FitMáx^©-questionnaire (hereafter FitMáx) (see Supplementary material online for the full English version ),⁷ and The Fitness Calculator (HFC),⁸ the latter is currently advised in healthy men and women by the American Heart Association.²

Objectives: Cardiorespiratory fitness plays an essential role in health outcomes and quality of life. Objective assessment of cardiorespiratory fitness is costly, labour intensive and not widely available. Although patient-reported outcome measures estimate cardiorespiratory fitness more cost-efficiently, the current questionnaires lack accuracy. The aim of this study is to develop and validate the FitMáx©-questionnaire, a self-reported questionnaire to estimate cardiorespiratory fitness in healthcare. Methods: We developed the FitMáx©-questionnaire, consisting of three questions assessing walking, stair climbing, and cycling capacity. A comparison on estimating VO _2peak was made with the Duke Activity Status Index (DASI), Veterans Specific Activity Questionnaire (VSAQ) and cardiopulmonary exercise testing as the gold standard. A total of 716 patients and athletes (520 men, 196 women) aged 18□91 performed a CPET in our hospital. We randomly selected 70% of the subjects to fit a linear regression model to estimate VO _2peak based on the FitMáx© scores. The remaining 30% of participants was used for validation of this model. Results: The VO _2peak estimated by the FitMáx© strongly correlates with the VO _2peak measured objectively with CPET; r=0.95 (0.93□0.96) SEE=3.94 ml·kg ^-1 ·min ^-1 . Bias between predicted and measured VO _2peak was 0.32 ml·kg ^-1 ·min ^-1 and the 95% limits of agreement were −8.11 □ 9.40 ml·kg ^-1 ·min ^-1 . In our sample, the FitMáx scored superiorly on correlation and SEE compared with those from the DASI and VSAQ, r=0.80 (0.73□0.86) SEE=4.22 ml·kg ^-1 ·min ^-1 and r=0.88 (0.84□0.91) SEE=6.61 ml·kg ^-1 ·min ^-1 , respectively. Conclusion: FitMáx© is a valid and accessible questionnaire to estimate cardiorespiratory fitness expressed as VO _2peak and shows substantial improvement compared to currently used questionnaires. Key points: FitMáx© relies on three simple single-answer questions, which are recognizable for a large population, to accurately estimate cardiorespiratory fitness. The FitMáx© is a self-reported instrument in which involvement of physicians, healthcare providers or other instrumentation is not necessary. Cardiorespiratory fitness estimated by the FitMáx© may serve as an easily applicable measure in clinical and non-clinical settings.

Purpose Low cardiorespiratory fitness (CRF) increases the risk of postoperative morbidity and mortality following major surgery. Assessing CRF preoperatively, by measuring peak oxygen uptake (VO_2peak) during cardiopulmonary exercise testing (CPET), is valuable yet not widely available. This study aimed to assess whether questionnaires could be used preoperatively to identify high-risk surgical patients. Methods Healthy participants and patients who underwent CPET completed the FitMáx, Duke Activity Status Index (DASI), the modified 4-questions DASI (M-DASI-4Q), Veterans-Specific Activity Questionnaire (VSAQ), and Metabolic Equivalents of Task (MET) questionnaire. Questionnaire-VO_2peak was compared with CPET-VO_2peak. Overall performance of the questionnaires was assessed by the area under the curve (AUC) of receiver operating characteristic (ROC) curves. Furthermore, corresponding to the Youden index or pre-specified levels, sensitivity, specificity, and predictive values were determined. Results In total, 361 participants were included. All questionnaires showed high AUC values to identify high-risk patients, defined on the basis of CPET-VO_2peak thresholds. FitMáx and VSAQ demonstrated superior results compared to the other questionnaires. Based on the Youden index, the optimal questionnaire-VO_2peak cut-off values were 20.6, 21.3, and 26.1 ml·kg⁻¹·min⁻¹ for the FitMáx and 16.3, 18.2, and 20.4 ml·kg⁻¹·min⁻¹ for the VSAQ corresponding to the VO_2peak thresholds 16.0, 18.2 and 24.5 ml·kg⁻¹·min⁻¹ respectively. Conclusion The ability to identify high-risk surgical patients preoperatively (defined by the CPET-VO_2peak thresholds) by the FitMáx and the VSAQ indicates that they could be used to identify high-risk surgical patients. Patients with a poor predicted VO_2peak ≤ 21.3 and ≤ 18.2 ml·kg⁻¹·min⁻¹, respectively for FitMáx and VSAQ, should be referred to formal preoperative (cardiopulmonary) exercise testing. Trial registration The study was registered as NL-OMON23304 in the Overview of Medical Research in the Netherlands, retrospectively at 28–04-2020.