Purpose: Rheumatoid arthritis (RA) and juvenile idiopathic arthritis (JIA) are inflammatory diseases which involve increased risk of cardiovascular disease (CVD). High intensity interval training (HIIT) is known to be effective in improving cardiovascular health. The aim of this study was to investigate whether 10 weeks of HIIT at 85-95% of HRmax would improve important risk factors of CVD in rheumatic patients, and if these patients would tolerate exercise intensities above today's recommendations.

Methods: Seven women with RA and eleven with adult-JIA, 20-50 years, were recruited to this cross-over study. Participants performed HIIT, consisting of 4 × 4 min intervals at 85-95% of HRmax twice a week for 10 weeks on spinning bikes. Maximal oxygen uptake (VO2max), heart rate recovery, blood pressure, body composition, and blood variables were measured before and after the exercise and control period. Disease activity was determined and questionnaire data were collected.

Results: HIIT resulted in 12.2% increase in VO2max and 2.9% improvement in heart rate recovery (p < 0.05). BMI, body fat, and waist circumference decreased 1.2, 1.0, and 1.6%, respectively, whereas muscle mass increased 0.6% (p < 0.05). A trend toward decreased CRP was detected after HIIT (p = 0.08). No changes were detected in disease activity or pain.

Conclusion: Despite rigorous high intensity exercise, no increase was detected in disease activity or pain, indicating that HIIT was well tolerated by these patients. Furthermore, HIIT had positive effects on several CVD risk factors. In light of this pilot study, HIIT seems like a promising non-pharmacological treatment strategy for patients with RA and adult-JIA.