This protocol describes a 6-month randomised, controlled exercise trial in patients with axial spondyloarthritis (axSpA) with re-randomization after 3-months. The primary outcome of the trial (disease activity) will be evaluated at 3-months. The exercise programme on trial comprises high intensity interval training (HIIT), muscular strength exercise and aerobic physical activity sessions of specified duration, frequency, and intensity. It also includes brief knowledge videos to empower the patient. The intervention is remotely delivered by the SPARK application with personalised follow-up including monitoring to ensure exercise progression and adherence to exercise intensity. The SPARK application is built on a platform delivered by ABEL Technologies (trademark) and is customised for patients with axSpA.

Main objectives: To assess if a digital personally tailored exercise program with remote follow-up can reduce disease activity measured by ankylosing spondylitis disease activity score (ASDAS) in patients with recently diagnosed axial spondyloarthritis (axSpA).

Main inclusion criteria Adults (> 18 years) with clinical diagnosis from a rheumatologist of axSpA within the last 2 years of inclusion also fulfilling the ankylosing spondylitis disease activity score (ASAS) classification criteria, who are biologic disease modifying anti-rheumatic drugs (bDMARD) naïve, and have an active disease (ASDAS ≥ 1.3)

Main exclusion criteria:

Active iridocyclitis, c-reactive protein (CRP) > 30, contraindication to high intensity interval training

Primary outcome Proportion of participants in ASDAS inactive (ASDAS < 1.3) at 3 months

Number of participants: 260 (with an anticipated drop-out rate of 15%)

Study design: A two-arm multi-centre, clinical trial, randomization 1:1 to either digital exercise intervention with remote follow-up or usual care.

Intervention: Exercise delivered through an application and with personalised follow-up by a coach through remote sessions (the participant and SPARK-coach are not at the same physical location) weekly. The exercise is progressively tailored to the fitness level of each participant. The program consists of 5 session per week on 3 different days including: two sessions with HIIT, 2 sessions with strength exercise, and one session with an aerobic exercise at moderate intensity. Goal for HIIT is 10 minutes two times per week at 85-95% of maximal heart rate (20 minutes in total). The exercise will be performed at a location of the participants' choice and data will be logged by a sports watch.

Efficacy assessments: ASDAS disease activity measure (4 patient reported questions and measure of CRP), Bath ankylosing spondylitis disease activity index (BASDAI).

Physical measure: cardiorespiratory fitness, in a subset of participants direct cardiopulmonary testing, muscular strength tests.

Psychological measures: Warwick and Edinburgh mental wellbeing scale (WEMWBS), EuroQol (EQ5D).

Medication: use of bDMARDs, use of NSAID

Safety assessments General physical examination and vital signs, laboratory tests as a part of usual clinical care, record of adverse events and serious adverse events, magnetic resonance imaging (MRI).

Inclusion Criteria:

• axSpA diagnosis within the last two years by a rheumatologist according to the ASAS criteria of 2009
• active disease (ASDAS > 1.3)

Exclusion Criteria:

• Active uveitis.
• CRP > 30.
• Former or current use of bDMARDs.
• Pregnancy or planned pregnancy within 6 months from inclusion.
• Absolute and relative contradictions to high intensity exercise according to the American College of Sports Medicine (ACSM)
• Other serious disease such as cancer.
• Patients incapable to follow the protocol or the control set-up with remote monitoring.

The randomization is performed by a study personnel not involved in data collection. Patients are asked not to inform their care-giver or the physiotherapist who perform the study tests which group the patient is allocated to.