Objective: This cross sectional study evaluated criterion and construct validity of field exercise tests and patient-reported questionnaires to estimate cardiorespiratory fitness (CRF) compared with cardiopulmonary exercise testing (CPET). It also aimed to identify the best alternative for CPET to evaluate CRF in clinical rehabilitation. 
Design: All patients performed CPET, the steep ramp test (SRT), the 6-minute walk test (6-MWT) and completed the Duke activity status index (DASI), veterans-specific activity questionnaire (VSAQ), and FitMáx© questionnaire (FitMáx) within 42 days in which no change in CRF was expected. Work rate at peak exercise at the steep ramp test (SRT-WRpeak, in W/kg), distance walked at the 6-MWT (6-MWD, in m), and oxygen uptake at peak exercise (VO2peak, in ml/kg/min) estimated by patient-reported questionnaires were compared with the objectively measured VO2peak during CPET. Moreover, SRT-WRpeak, 6-MWD, and questionnaire-estimated VO2peak were compared to each other.  
Setting: Two physical therapy departments.
Participants: Sixty-nine patients (57% female) with cardiopulmonary or oncologic conditions  with a median (IQR) age of 58 (46-66) years. 
Interventions: Exercise rehabilitation. 
Main outcome measures: Pearson’s correlation between CPET-VO2peak and SRT-WRpeak, 6-MWD, and questionnaire-estimated VO2peak.
Results: Correlations of SRT-WRpeak and 6-MWD with CPET-VO2peak were r=0.83 (95% confidence interval (CI) 0.73-0.89) and r=0.43 (95% CI 0.21-0.60), respectively. Correlations of the DASI-VO2peak, VSAQ-VO2peak, and FitMáx-VO2peak with CPET-VO2peak were r=0.36 (95% CI 0.13-0.55), r=0.43 (95% CI 0.22-0.61), and r=0.76 (95% CI 0.64-0.84), respectively. 
Conclusions: Both SRT-WRpeak and FitMáx-VO2peak showed a strong correlation with CPET-VO2peak. The 6-MWD, DASI-VO2peak and VSAQ-VO2peak showed a poor correlation with CPET-VO2peak. Consequently, the SRT and FitMáx are considered the best alternative field exercise test and patient-reported questionnaire to estimate CRF when CPET is not feasible or considered redundant.

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.

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.