ObjectivePatients with rheumatoid arthritis (RA) suffer from more cardiovascular disease (CVD), and develop cardiovascular risk factors at an earlier age than the general population. Cardiorespiratory fitness (CRF) is an important predictor of cardiovascular health. There are few data regarding CRF of RA patients, measured as peak oxygen uptake (VO2peak) by the gold standard method; cardiopulmonary exercise testing. We compared CRF in RA patients to those from a healthy population, and investigated if risk factors for CVD and RA-specific variables including subjective and objective disease activity measures were associated with CRF in RA patients.MethodsVO2peak tests of RA patients (n=93) were compared to those of an age-matched and gender-matched healthy population (n=4631) from the Nord-Trøndelag Health Study. Predictors of VO2peak were found using Lasso (least absolute shrinkage and selection operator) regression, followed by standardised multiple linear regression.ResultsWomen with RA ≥40 years and men with RA aged 40–49 years or 60–69 years had up to 20% lower CRF than the healthy population in the same age groups. By relative importance, body mass index (standardised coefficient=−0.25, p<0.001), physical activity level (coefficient=0.21, p<0.001), patient global assessment (PGA; coefficient=−0.14, p=0.006), systolic blood pressure (coefficient=−0.12, p=0.016), resting heart rate (coefficient=−0.11, p=0.032) and smoking (coefficient=−0.10, p=0.046) were significant predictors of CRF (R2=0.82, gender-adjusted and age-adjusted).ConclusionCRF in RA patients was lower than in a healthy population. CRF was associated with common risk factors for CVD and the PGA score. Focusing on fitness in RA patients may improve cardiovascular health.

Purpose Cardiopulmonary exercise testing of peak oxygen uptake (V˙O2peak) is the gold standard to measure cardiorespiratory fitness (CRF). For resource-intensive evaluation, equations estimating CRF (eCRF) may be used. The purpose was to investigate if an eCRF equation from a healthy population is useful in persons with rheumatoid arthritis (RA), and if necessary, develop new equations for eCRF in this group. Methods V˙O2peak results from 93 persons with RA were compared with eCRF calculated by an established equation for healthy individuals including age, sex, physical activity (PA index), resting HR (RHR), and waist circumference. Because of deviation from the observed V˙O2peak, new equations for eCRF in persons with RA were developed from regression analysis of variables associated with observed V˙O2peak. Results The established equation overestimated CRF (R 2 = 0.48, root mean square error [RMSE] = 7.07). The new RA equation more accurately estimated CRF (R 2 = 0.81, RMSE = 4.44) (female = 0, male = 1; never smoked = 0, ever smoked = 1): eCRF = 77.961 + (sex × 28.791) − (age × 0.358) − (age–sex interaction × 0.326) − (body mass index [BMI] × 0.700) − (RHR × 0.125) − (smoking × 1.854) + (PA index × 0.211) − (patient global RA assessment × 0.071). Alternative new RA equation (R 2 = 0.79, RMSE = 4.63): eCRF = 77.851 + (sex × 25.460) − (age × 0.381) − (age–sex interaction × 0.254) − (BMI × 0.743) − (RHR × 0.115) − (smoking × 2.154) + (PA index × 0.209). Conclusions The new RA equations better predicted CRF in individuals with RA, preventing overestimation in low-fit persons. The new equation should be preferred when estimating CRF in individuals with RA. The alternative equation, without patient global assessment, is useful for individuals with RA in population-based studies.