Cardiorespiratory fitness in patients with rheumatoid arthritis is associated with the patient global assessment but not with objective measurements of disease activity

Self-determined motivation and physical activity in patients with rheumatoid arthritis: a cross-sectional study

OBJECTIVE

To identify factors associated with two self-reported measures of physical activity (PA) in patients with rheumatoid arthritis (RA).

METHOD

Hospital outpatients with RA from central Norway filled in questionnaires about symptoms, psychological factors, and PA. Outcomes were two alternative self-reported measures of PA: (i) fulfilling the aerobic PA recommendations of ≥ 150 min/week at moderate intensity or ≥ 75 min/week at vigorous intensity; or (ii) being in the PA maintenance stage of the Stages of Exercise Behaviour Change framework. Logistic regression was applied to identify factors associated with PA. Step 1 included the independent variables sex, age, and smoking habits. Step 2a added self-reported function, joint pain during the past 6 months, and fatigue to Step 1. Step 2b added Exercise Self-Efficacy and the Relative Autonomy Index (RAI), calculated from the Behavioural Regulation in Exercise Questionnaire-2, to Step 1. Step 3 included all the mentioned independent variables. Steps 1-3 were analysed for each PA measure.

RESULTS

In total, 227 patients participated. The RAI had a statistically significant positive association with being physically active according to both PA definitions. Joint pain had a significant negative association with meeting the aerobic PA recommendations but was not associated with being in the PA maintenance stage.

CONCLUSION

The degree of self-determined motivation was the most consistent variable associated with self-reported PA behaviour. Joint pain was associated with one of the two PA measures. Motivation and joint pain may be useful targets for intervention in clinical practice to improve PA engagement among patients with RA.

Effect of high-intensity interval training in physiotherapy primary care for patients with inflammatory arthritis: the ExeHeart randomised controlled trial

OBJECTIVES

To assess the effect of high-intensity interval training (HIIT) delivered in physiotherapy primary care on the primary outcome of cardiorespiratory fitness (CRF) in patients with inflammatory arthritis (IA). Additionally, to explore the effects of HIIT on secondary outcomes, including cardiovascular disease (CVD) risk factors and disease activity.

METHODS

Single-blinded randomised controlled trial with 60 patients randomly assigned to either a control group receiving usual care or an exercise group receiving usual care and 12 weeks of individualised HIIT at 90%-95% peak heart rate. Outcomes were assessed at baseline, 3 months and 6 months post baseline and included CRF measured as peak oxygen uptake (VO2peak), classic CVD risk factors, disease activity, anthropometry and patient-reported physical activity, pain, fatigue, disease impact and exercise beliefs and self-efficacy.

RESULTS

Intention-to-treat analysis demonstrated a significant between-group difference in VO2peak at 3 months (2.5 mL/kg/min, 95% CI 0.9 to 4.0) and 6 months (2.6 mL/kg/min, 95% CI 0.8 to 4.3) in favour of the exercise group. A beneficial change in self-reported physical activity in favour of the exercise group was observed at 3 and 6 months. The HIIT intervention was well-tolerated with minimal adverse events and no apparent impact on disease activity. Differences in secondary outcomes related to CVD risk factors, disease impact, pain, fatigue and exercise beliefs and self-efficacy were generally small and non-significant.

CONCLUSION

After 12 weeks of supervised HIIT delivered in physiotherapy primary care, patients with IA demonstrated a favourable improvement in CRF, with sustained effects at 6-month follow-up.

TRIAL REGISTRATION NUMBER

NCT04922840.

Exercise therapy for improving cardiovascular health in rheumatoid arthritis

There is increased risk of cardiovascular disease in patients with rheumatoid arthritis. Primary cardiovascular disease prevention in rheumatoid arthritis patients is difficult, especially in those with high disease activity. According to current evidence, people with rheumatoid arthritis can significantly improve clinical indices and patient-reported outcomes by engaging in organized physical activity such as resistance training and aerobic activities. Additionally, participating in an exercise regimen can lower the risk of experiencing cardiovascular problems. Nevertheless, the percentage of patients with sedentary lifestyle habits is high among individuals with rheumatoid arthritis. Patient education regarding the benefits of physical activity/exercise is essential. The cardiovascular effects of exercise depend on several mechanisms such as (i) increased vascular function, (ii) decreased systemic inflammation, (iii) restoration of the autonomic system, (iv) improved lipid profile, and (v) increased muscular function. Maintaining the exercise routine is crucial for continuing benefits. A customized exercise plan helps to improve adherence and compliance. Engaging patients in shared decision-making is important since their personal choices can alter depending on several factors such as the severity of the disease, the cost, and accessibility. The current narrative review aimed to explore the recent evidence related to exercise therapy for cardiovascular health in patients with rheumatoid arthritis.

Relative importance of inflammation and cardiorespiratory fitness for all-cause mortality risk in persons with rheumatoid arthritis: the population-based Trøndelag Health Study

OBJECTIVE

Inflammation and reduced cardiorespiratory fitness (CRF) are associated with increased mortality rates in rheumatoid arthritis (RA). We aimed at directly comparing the relative importance of inflammation and reduced CRF as mediators of all-cause mortality in persons with RA compared with controls, quantifying direct and indirect (mediated) effects.

METHODS

Persons with (n=223, cases) and without (n=31 684, controls) RA from the third survey of the Trøndelag Health Study (HUNT3, 2006-2008) were included. Inflammation was quantified using C reactive protein (CRP) and estimated CRF (eCRF) was calculated using published formulae. All-cause mortality was found by linkage to the Norwegian Cause of Death Registry, with follow-up from inclusion in HUNT3 until death or 31 December 2018. Data were analysed using standardised equation modelling, permitting complex correlations among variables.

RESULTS

Persons with RA had increased all-cause mortality rates (24.1% vs 9.9%, p<0.001). Both eCRF (p<0.001) and CRP ≥3 mg/L (p<0.001) were mediators of this excess mortality, rendering the direct effect of RA non-significant (p=0.19). The indirect effect of RA mediated by eCRF (standardised coefficient 0.006) was approximately three times higher than the indirect effect mediated by CRP (standardised coefficient 0.002) in a model adjusted for other mortality risk factors.

CONCLUSION

Even with CRP concentrations <3 mg/L in all patients with RA, excess mortality mediated by low CRF would still play an important role. Improved inflammation control in RA does not necessarily lead to better CRF. Therefore, our study strongly supports recommendations for development and implementation of exercise programmes aimed at improving CRF in persons with RA.

Associations between cardiovascular risk factors, disease activity and cardiorespiratory fitness in patients with inflammatory joint disease: a cross-sectional analysis

BACKGROUND

Inflammatory joint diseases (IJD) are accompanied by an increased risk of cardiovascular disease (CVD). Cardiorespiratory fitness (CRF) is a modifiable CVD risk factor and low levels of CRF associate with an elevated CVD risk. This study aimed to investigate the associations between CVD risk factors, disease activity and CRF in patients with IJD and to explore differences between patients with normal versus low levels of CRF.

METHODS

CRF was measured as peak oxygen uptake (VO_2peak) with a cardiopulmonary exercise test. Participants were also evaluated for: Body composition, blood pressure, blood lipids, inflammatory markers and disease activity. Patient-reported use of cigarettes/snuff, medication, disease duration, pain, fatigue, CVD history, habitual physical activity and exercise beliefs and self-efficacy were collected by questionnaire. Cross-sectional associations between CVD risk factors, disease-related factors and CRF were analyzed by multiple linear regression. CRF was categorized to normal CRF (VO_2peak ≥ 80%) or low CRF (VO_2peak < 80%) according to age- and gender-stratified reference data. Differences in demographic, CVD and disease-related factors between patients with normal versus low CRF were explored.

RESULTS

In 60 Norwegian patients with IJD [34 females, age 59 years (IQR: 52-63)], mean VO_2peak was 30.2 (± 6.9) mL/kg/min, corresponding to 83% (± 18) of normative reference values. Age (coefficient: - 0.18 years, p = 0.01) and fat mass (coefficient: - 0.67 %, p < 0.001) were inversely associated with CRF, while physical activity index (coefficient: 0.13 points, p = 0.05) was positively associated with CRF (R² = 0.66). There were no significant associations between CRF, classical CVD risk factors and disease-related variables. Compared to patients with low CRF (n = 30), patients with normal CRF (n = 30) had higher peak oxygen uptake (+ 9.4 mL/kg/min, p < 0.001), high-density lipoprotein cholesterol (+ 0.5 mmol L^-1, p < 0.001), and exercise self-efficacy (+ 6.9, p < 0.01) as well as lower fat mass (- 8.7%, p < 0.001), resting heart rate (- 8.0 beats/min, p < 0.01) and triglycerides (- 0.5 mmol L^-1, p < 0.01).

CONCLUSIONS

In this sample of IJD-patients, age, fatmass and physical activity level were associated with CRF. CRF was lower than reference values and patients with normal CRF presented with a more favorable health profile. There is a continued need for exercise interventions to improve CRF in patients with IJD.

TRIAL REGISTRATION

NCT04922840.

The association between rheumatoid arthritis and reduced estimated cardiorespiratory fitness is mediated by physical symptoms and negative emotions: a cross-sectional study

OBJECTIVES

Persons with rheumatoid arthritis (RA) have lower cardiorespiratory fitness (CRF) than healthy individuals. We sought to identify variables explaining the association between RA status and reduced CRF.

METHODS

RA patients recruited from two Norwegian hospitals and blood donors recruited as controls filled in questionnaires about physical activity, physical symptoms, and psychological factors. Estimated CRF (eCRF) was calculated from non-exercise models. The relationship between RA status and reduced eCRF was explored with structural equation modelling. The latent variables physical symptoms (based on morning stiffness, joint pain, and pain in neck, back, or hips) and negative emotions (based on Hospital Anxiety and Depression Scale's Depression score and Cohen's perceived stress scale) were included as possible mediators between RA status and eCRF in separate and combined models adjusted for age and sex.

RESULTS

Two-hundred-and-twenty-seven RA patients and 300 controls participated. The patients were older and had lower eCRF than controls (age- and sex-adjusted mean difference: 1.7 mL/kg/min, p=0.002). Both latent variables were significant mediators of the association between RA and reduced eCRF when included in separate models. The latent variables mediated 74% of the total effect of RA on eCRF in the combined model. Standardized coefficients: direct effect of RA -0.024 (p=0.46), indirect effect through physical symptoms -0.034 (p=0.051), and indirect effect through negative emotions -0.034 (p=0.039).

CONCLUSION

Both physical symptoms and negative emotions mediated the association between RA and reduced eCRF with similar effect sizes. To successfully increase CRF in RA patients, both physical and psychological factors should be addressed. Key Points • The RA patients in the present study had 1.7 mL/kg/min lower mean estimated cardiorespiratory fitness (CRF) compared to healthy controls. • Mediation analysis demonstrated that physical symptoms and negative emotions mediated 74% of the total negative effect of RA on estimated CRF in a combined, adjusted model. • This suggests that both physical and psychological factors should be addressed when supporting RA patients in improving their CRF.

Persons with rheumatoid arthritis have higher barriers to physical activity than controls: a cross-sectional study using the Facilitators and Barriers to Physical Activity Questionnaire (FasBarPAQ)

Facilitators and barriers to performing physical activity (PA) may vary among persons with rheumatoid arthritis (RA) as well as between RA patients and healthy individuals. Primary objective: To investigate associations of presence of RA and levels of stress and depression with scores for facilitators and barriers to PA, using a new questionnaire (FasBarPAQ). Secondary objectives: investigate inter-individual score differences in persons with RA, and associations with RA disease-specific variables. Persons with RA from two outpatient clinics (n = 203) and blood donor controls (n = 293) filled in the new 14-item FasBarPAQ questionnaire, the Hospital Anxiety and Depression Scale depression scale (HADS-D), Cohen's perceived stress scale, and questions regarding PA. Clinical data, and self-reported disease activity and physical function were collected for the persons with RA. Data were analyzed using linear and logistic regression. RA was associated with lower Facilitators scores (coefficient = - 1.30, p = 0.015), higher Barriers scores (coefficient = 2.36, p < 0.001) and lower Total Facilitators-Barriers scores (coefficient = - 3.67, p < 0.001). HADS-D ≥ 8 was associated with lower Total scores (coefficient = - 3.32, p = 0.022), and the two higher stress score tertiles were associated with higher Barriers and lower Total scores (p = 0.023 to p < 0.001). Persons with RA reported greatly varying facilitators and barriers profiles. Seropositivity and higher patient global assessment were associated with higher Barriers scores (coefficients = 1.79, p = 0.011; 0.60, p < 0.001) and lower Total scores (coefficients = - 3.60, p = 0.003; - 0.98, p < 0.001). Persons with RA had higher barriers and lower facilitators for PA, with varying individual profiles. The new FasBarPAQ questionnaire may be a useful screening tool for healthcare providers treating persons with RA.

Rehabilitation goals described by patients with rheumatic and musculoskeletal diseases: content and attainment during the first year after rehabilitation

PURPOSE

We explored the content and attainment of rehabilitation goals the first year after rehabilitation among patients with rheumatic and musculoskeletal diseases.

METHODS

Participants (n = 523) recorded goals in the Patient Specific Functional Scale at admission and reported goal attainment at admission, discharge, and 12 months after rehabilitation on an 11-point numeric rating scale. Goal content was linked to the ICF coding system and summarized as high, maintained, or no attainment. Changes in absolute scores were investigated using paired samples t-tests.

RESULTS

Goals had high attainment with a significant positive change (-1.83 [95% CI -2.0, -1.65], p > 0.001) during rehabilitation, whereas goals had no attainment with a significant negative change (0.36 [0.14, 0.57], p > 0.001) between discharge and 12 months after rehabilitation. Goals focusing on everyday routines, physical health, pain management, and social or work participation were highly attained during rehabilitation. Goals that were difficult to enhance or maintain after rehabilitation addressed everyday routines, physical health, and work participation.

CONCLUSION

The positive changes in goal attainment largely occurred during rehabilitation, but they appeared more difficult to maintain at home. Therefore, rehabilitation goals should be reflected in the follow-up care planned at discharge.Implications for rehabilitationThe contents of rehabilitation goals reflect the complexity and wide range of challenges patients with rheumatic and musculoskeletal diseases experience.Positive changes in goal attainment largely occur during rehabilitation and appear to be more difficult to enhance or maintain at home.Rehabilitation interventions and follow-up care should be tailored to support patients in maintaining their attained goals for healthy self-management.Rehabilitation goals should be reflected in the follow-up care planned at discharge.

Exercise Self-Efficacy and patient global assessment were associated with 6-min walk test distance in persons with rheumatoid arthritis

INTRODUCTION

Low functional capacity is related to future loss of daily function and cardiovascular events. The present study explored the associations of patient-reported outcome measures (PROMs) and disease-specific measures with functional capacity as measured by the 6-min walk test (6MWT) in persons with rheumatoid arthritis (RA).

METHODS

Seventy-nine participants from rheumatology outpatient clinics were included. The distance walked during the 6MWT (6MWD) was the dependent variable in multivariable regression analyses. Model 1 included the independent variables sex, age (in tertiles to improve model fit), and body mass index (BMI). Building on Model 1, Model 2 added smoking, patient global assessment (PGA), Exercise Self-Efficacy, Hospital Anxiety and Depression Scale's Depression score, and Cohen's Perceived Stress Scale score, whereas Model 3 added smoking, disease duration, present use of glucocorticosteroids, seropositivity, Disease Activity Score 28-C-Reactive Protein (DAS28-CRP), and a comorbidity variable.

RESULTS

Median age was 65 years, 76% were female, and median 6MWD was 493 m. In Model 1, BMI and age were significantly associated with the 6MWD (R2 = 0.42). In Model 2, PGA and Exercise Self-Efficacy were also significantly associated with the 6MWD, with standardized regression coefficients of - 0.21 (p = 0.03) and 0.26 (p = 0.004) respectively (R2 = 0.54). The RA-specific variables in Model 3 were not significantly associated with the 6MWD (R2 = 0.49).

CONCLUSION

The PROMs PGA and Exercise Self-Efficacy were significantly associated with functional capacity as measured by the 6MWT in persons with RA, whereas disease-specific measures such as DAS28-CRP and disease duration were not. Key Points • Functional capacity measured with the 6-minute walk test was significantly associated with body mass index, age, patient global assessment, and Exercise Self-Efficacy in persons with RA. • Patient-reported outcome measures explained more of the variation in functional capacity than objective or composite measures of disease and are relevant measures in clinical follow-up. • Techniques that enhance self-efficacy for exercise should be incorporated into clinical practice to promote physical activity.

The impact of a structured weight-loss treatment on physical fitness in patients with psoriatic arthritis and obesity compared to matched controls: a prospective interventional study

Objectives

To evaluate the effects of weight loss treatment on physical fitness in patients with psoriatic arthritis (PsA) and obesity compared to matched controls.

Methods

In total, 46 patients with PsA (CASPAR) and BMI ≥ 33 kg/m² and 52 obese persons were included in this 12-month prospective open intervention study with a very low energy diet (640 kcal/day), followed by structured reintroduction of an energy-restricted diet and brief support for physical activity. The primary outcome was muscle strength assessed with hand-grip strength (Grippit) and leg muscle strength (timed stand test). Secondary outcomes were cardiorespiratory fitness, body composition, and physical functioning (SF-36PCS). Outcomes were assessed at baseline, 6 (M6), and 12 months (M12). Nonparametric statistics were used.

Results

Median weight reduction at M6 was 18.9 kg in patients and 23.0 kg in controls, (p = 0.546). At M12, patients’ median weight loss from baseline was 16.1 kg, corresponding with significant loss of total fat mass (− 30.1%), and lean mass (total − 7.0%, arm − 13.7%, and leg − 6.0%). Leg muscle strength improved in patients and controls at M6 (p < 0.001) and remained improved at M12 (p < 0.01), while hand-grip strength was unchanged in both groups. Cardiorespiratory fitness increased in controls at M6 (p = 0.018) and M12 (p = 0.028) but not in patients. Physical functioning improved in both groups at M6 (p < 0.001) and remained improved at M12 (p = 0.008) and (p < 0.01), respectively.

Conclusion

The intervention resulted in positive effects on body weight and total body fat. Despite reduced lean body mass, the muscle strength did not deteriorate in patients with PsA and controls.

Trial registration

ClinicalTrials.gov identifier: NCT02917434, registered on September 21, 2016-retrospectively registered.

Use of the Behavioral Regulation in Exercise Questionnaire-2 to assess motivation for physical activity in persons with rheumatoid arthritis: an observational study

Arthritis patients may show little motivation for physical activity (PA), resulting in a sedentary lifestyle. The primary objective of the study was to investigate whether motivation for PA and fulfillment of PA recommendations were associated with cardiorespiratory fitness in patients with RA. The exploratory objective was to study whether university students could be used as controls for RA patients in future studies of PA motivation. Peak oxygen uptake (VO_2peak) was measured in 93 RA patients. The patients and 354 students filled in the Behavioral Regulation in Exercise Questionnaire-2 (BREQ-2). Data were analyzed using structural equation modeling with adjustment for age and sex. The BREQ-2 scores were also compiled to an overall motivational style “Relative Autonomy Index” as previously published. Mean VO_2peak for the RA patients was 32.2 (SD: 9.6) mL × min⁻¹ × kg⁻¹. Only 29 patients (31%) fulfilled the current recommendations for PA. BREQ-2 scores were associated with measured VO_2peak (standardized coefficient 0.33, p < 0.001). Whether a person fulfilled the current recommendations for PA was a significant mediator of this effect (standardized coefficients: mediated effect; 0.22, p = 0.001, remaining direct effect; 0.11, p = 0.18). The Relative Autonomy Index also significantly predicted measured VO_2peak (standardized coefficient 0.30, p < 0.001). The underlying BREQ-2 factor structure was significantly different between RA patients and university students, and comparison of scores would not be adequate. Motivation for PA was significantly associated with measured VO_2peak in RA patients. The effect was mediated by whether the patient fulfilled the current recommendations for PA. Addressing and stimulating motivation is important when intervening to increase PA and cardiovascular fitness in RA patients.

Influence of perceived barriers and facilitators for physical activity on physical activity levels in patients with rheumatoid arthritis or spondyloarthritis: a cross-sectional study of 150 patients

Background

Barriers and facilitators to physical activity in inflammatory arthritis can be assessed through the Inflammatory arthritis FAcilitators and Barriers (IFAB) questionnaire. The objective was to measure the correlation between IFAB and self-reported physical activity levels.

Methods

This was an international, multicentric, cross-sectional study in 2019–20. Consecutive spondyloarthritis (axSpA), rheumatoid arthritis (RA) or psoriatic arthritis (PsA) patients completed the 10-item IFAB, which ranges from − 70 to 70 with lower scores indicating more barriers. Physical activity was measured by the IPAQ-S questionnaire, steps per day collected by smartphone, and psychological readiness to change by stages of behaviour change. Spearman correlations and multivariable linear regression were calculated.

Results

Of 245 patients included, 150 were analysed: 69 (46%) axSpA, 63 (42%) RA, 18 (12%) PsA. Mean age was 48.6 years (standard deviation, SD 17.1), mean disease duration 11.7 (10.1) years and 60% were women. Barriers to physical activity were moderate: mean IFAB, 6 (SD 19.2); 39 (26%) patients scored less than − 5, corresponding to significant barriers. The mean physical activity was 2837 (SD 2668, median 1784) MET-minutes per week. The IPAQ-S questionnaire was correlated with the IFAB (rho 0.28, p < 0.001), as well as the stage of behaviour change (rho 0.35, p < 0.001) though not with steps per day. Multivariable analyses were confirmatory.

Conclusion

Perceived barriers and facilitators to physical activity were correlated with physical activity, indicating that targeting patients with high barriers and low facilitators to physical activity could be an effective option to improve physical activity levels.

Trial registration

ClinicalTrial NCT04426747. Registered 11 June 2020 - Retrospectively registered.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04792-7.

Reduced cardiorespiratory fitness is a mediator of excess all-cause mortality in rheumatoid arthritis: the Trøndelag Health Study

Objectives

Investigate if low cardiorespiratory fitness (CRF) was associated with and acted as a mediator of excess all-cause mortality rate in persons suffering from rheumatoid arthritis (RA) compared with the general population.

Methods

All-cause mortality was analysed using Cox regression modelling in patients with RA (n=348) and controls (n=60 938) who took part in the second (1995–1997) and third (2006–2008) waves of the longitudinal population-based Trøndelag Health Study in Norway. A mediation analysis was performed to investigate if excess relative risk of mortality in RA was mediated by low estimated CRF (eCRF).

Results

During the follow-up until 31 December 2018 (mean 19.3 years), the mortality rate among patients with RA (n=127, 36.5%) was higher than among controls (n=12 942, 21.2%) (p<0.001). Among controls and patients with RA, 51% and 26%, respectively, had eCRF above the median for their age and sex (p<0.001). The final Cox model included RA status and eCRF, adjusted for hypertension, body mass index, smoking, cholesterol, diabetes and creatinine. eCRF below median for sex and age category was associated with increased mortality (p<0.001). The total excess relative risk of mortality in patients with RA was 28% (95% CI 2% to 55%, p=0.035), in which RA itself contributed 5% and the direct and indirect contributions of low eCRF accounted for 23%.

Conclusions

Low eCRF was an important mediator of the increased all-cause mortality rate found in RA. Our data indicate that patients with RA should be given advice to perform physical activity that increases CRF, along with optimised treatment with antirheumatic drugs, from the time of diagnosis.

An Estimation Model for Cardiorespiratory Fitness in Adults with Rheumatoid Arthritis

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 = 0.48, root mean square error [RMSE] = 7.07). The new RA equation more accurately estimated CRF (R = 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 = 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.

Faster age-related decline in cardiorespiratory fitness in rheumatoid arthritis patients: an observational study in the Trøndelag Health Study

Primary aim: Compare change in estimated cardiorespiratory fitness (eCRF change) in rheumatoid arthritis (RA) patients with population-based age- and sex-matched controls during ~ 11-year follow-up and identify variables associated with eCRF change. Secondary aim: Compare eCRF level in RA patients and controls. eCRF change from the second (HUNT2 1995–1997) to the third (HUNT3 2006–2008) surveys of the Norwegian Trøndelag Health Study was compared between RA patients (n = 188) and controls (n = 26,202) attending both surveys. Predictors of eCRF change were identified by Lasso regression followed by multiple linear regression. Mean eCRF level in RA patients (n = 436) and controls (n = 67,910) was compared using age-adjusted linear regression stratified on sex, as well as two-sample t tests including RA patients (n = 432) and controls (n = 59,124) who attended either HUNT2, HUNT3 or both HUNT2 and HUNT3. The mean eCRF decline from HUNT2 to HUNT3 in RA patients was 8.3 mL min⁻¹ kg⁻¹ versus 6.7 mL min⁻¹ kg⁻¹ in controls (p < 0.001). The decline was faster in RA patients and larger with higher baseline age (standardized regression coefficient for RA patients: (− 0.482 × age + 0.044); controls: (− 0.367 × age, p < 0.001). The decline was also associated with smoking, cardiovascular disease, increasing body mass index, asthma, and hypertension. Mean differences in age-adjusted eCRF level for RA patients versus controls (p < 0.001): women HUNT2: − 3.2 mL min⁻¹ kg⁻¹; HUNT3: − 5.0 mL min⁻¹ kg⁻¹; men HUNT2: − 1.8 mL min⁻¹ kg⁻¹; HUNT3: − 4.0 mL min⁻¹ kg⁻¹. Higher age at baseline was associated with faster decline in eCRF. This change was more pronounced in RA patients than controls, indicating a larger negative effect on fitness of aging in RA. RA patients had lower eCRF compared to healthy individuals.