Background Exercise is considered important in the management of patients with rheumatic diseases, but the effect of high intensity exercises on disease activity is unknown.

Objective To investigate the effectiveness of high intensity exercises on disease activity in patients with axial spondyloarthritis (axSpA).

Method Assessor blinded multicentre randomised controlled trial. 100 patients (aged from their 20s to their 60s) with axSpA were randomly assigned to an exercise group or to a no-intervention control group. The exercise group performed cardiorespiratory and muscular strength exercises at high intensity over 3 months. The control group received standard care and was instructed to maintain their usual physical activity level. Primary outcome was disease activity measured with the Ankylosing Spondylitis (AS) Disease Activity Scale (ASDAS, higher score=worst) and the Bath AS Disease Activity Index (BASDAI, 0–10, 10=worst). Secondary outcomes were inflammatory markers, physical function and cardiovascular (CV)-health. There was patient involvement in the design and reporting of this study.

Results 97 of the 100 (97%) randomised patients completed the measurements after the intervention. There was a significant treatment effect of the intervention on the primary outcome (ASDAS: −0.6 [–0.8 to –0.3], p<0.001 and BASDAI: −1.2 [–1.8 to –0.7], p<0.001). Significant treatment effects were also seen for inflammation, physical function and CV-health.

Conclusion High intensity exercises reduced disease symptoms (pain, fatigue, stiffness) and also inflammation in patients with axSpA. It improves patients’ function and CV health. This debunks concerns that high intensity exercise might exacerbate disease activity in patients with axSpA.

Trial registration number NCT02356874.