Assessment of Cardiorespiratory Fitness in Spondylarthritis

Spondyloarthritis is a chronic inflammatory joint disease that affects the spine and sacroiliac joints. Most untreated patients eventually experience impaired mobility of the spine, pain and reduced physical function. Exercise is a cornerstone in the treatment of patients with spondylarthritis and it has been shown that high intensity exercise is just as effective in reducing disease activity as immunosuppressive medication. Additionally, patients with spondylarthritis have increased risk of cardiovascular disease both due to traditionally risk factors (obesity, high blood pressure etc) but also due to chronic inflammation. A maximal cardiopulmonary exercise test (CPET) is a measure of cardiorespiratory fitness that can be used to show progression of the exercise and which also is correlated to all-cause mortality and life expectancy. The investigators will validate an indirect maximal CPET against the gold standard with direct gas exchange measurements in patients with spondylarthritis. The indirect test is less time consuming, requires less sophisticated equipment, has lesser requirements to test personnel and facilities, and has less expenditures than the direct test. With a validated indirect maximal CPET the test of cardiorespiratory fitness will be more accessible for patients with spondylarthritis both in-hospital but also municipal.