Background: High-intensity interval training (HIIT) has been shown to reduce symptoms and risk of cardiovascular comorbidity for individuals with axial spondyloarthritis (axSpA) without exacerbating disease activity [1]. However, supervised exercise is resource-intensive and clinically difficult to manage. Also, adherence to HIIT tends to decrease over time which can have implications for determining the effects of HIIT [2]. More knowledge on adherence to self-managed HIIT is needed to tailor training individually and provide sustainable exercise routines.

Objectives: To study adherence of attendance, duration and intensity in a 12-week intervention with self-managed digitally based HIIT among individuals with axSpA and whether adherence changes for each four-week block during the intervention.

Methods: This study is part of an ongoing RCT including 44 participants, recruited from rheumatology clinics in southern Sweden. The participants were randomized to a HIIT intervention group (HIIT-G; n= 22) or to a control group (not included in this analysis). The HIIT-G conducted three high-intensity training sessions/week for 12 weeks and were regularly digitally coached by a physiotherapist. Two sessions per week were interval training in self-selected activities. All participants were equipped with a fitness watch measuring the heart rate (HR) continuously during the training sessions. The fitness watch had three preset HIIT protocols, 4x4/ 5x3/ 8x2 minutes. The HIIT-G participants were instructed to get at least a total of 15 minutes of interval time in each session, and to reach at least 90% of their maximum HR (HR _max ) at some point during each interval. Sex, age, self-reported disease activity (BASDAI, 0-10 best-worst), physical function (BASFI, 0-10 best-worst), health status (EQ-5D, 0-1 worst-best) and assessment of aerobic capacity (VO ₂ max, mlO ₂ /kg/min) at baseline were used to describe the HIIT-G characteristics. Adherence to attendance was measured as the number of sessions attended compared to sessions prescribed. Adherence to duration was set as a cut-off where only training sessions ≥30 minutes were included in the analysis. Adherence to intensity was measured as 1) the number of sessions where the participants reached at least one minute in HR ≥90% of HR _max (1min HR≥90) and 2) minutes in HR zone ≥90% of HR _max (HR≥90). Statistics included comparisons between each block of four weeks (month 1 – 3; M1, M2, M3), using one-way repeated measures ANOVA. In case of significant ANOVA, post-hoc analyses were made.

Results: Results are based on 20 participants (women n=10) who completed the 12-week HIIT intervention (two dropouts). The participants mean ± SD age was 45 ± 12 years, BASDAI 2.8 ± 1.2, BASFI 1.4 ± 1.1, EQ-5D 0.8 ± 0.1, and VO ₂ max 35 ± 8 mlO ₂ /kg/min. Over the 12 weeks, participants completed 30.2 ± 5.7 sessions which corresponds to 84% of the 36 prescribed sessions. Moreover, over 12 weeks they reached 1min HR≥90 in 16.8 ± 7.6 sessions (55% of attended sessions) and spent a total of 94.0 ± 68.4 minutes in HR≥90 (Table 1). Analyses between M1, M2, and M3 showed that attendance decreased significantly from 11.0 ± 1.1 (92%) sessions in M1 to 9.2 ± 3.0 (77%) sessions in M3 (ANOVA p=0.03; Table 1). The participants reached 1min HR≥90 in 59% of attended sessions in M1 and 52% of attended sessions in both M2 and M3 (ANOVA p=0.06). The time spent in HR>90 did not change significantly, with 34.3 ± 20.1 minutes in M1, 30.7 ± 27.5 minutes M2 and 29.0 ± 30.0 minutes M3 (ANOVA p=0.36; Table 1).

Conclusion: This study shows high adherence of attendance to self-managed digitally based HIIT among individuals with axSpA, performed outside the healthcare settings and with support of a physiotherapist. The participants reached 1min HR≥90 in more than half of the sessions attended. Adherence of attendance decreased over time, but the time spent in zone HR≥90 did not change.

REFERENCES: [1] Sveaas SH, Bilberg A, Berg IJ, Provan SA, Rollefstad S, Semb AG, et al. High intensity exercise for 3 months reduces disease activity in axial spondyloarthritis (axSpA): a multicentre randomised trial of 100 patients. Br J Sports Med. 2019.

[2] Taylor JL, Holland DJ, Keating SE, Bonikowske AR, Coombes JS. Adherence to High-intensity Interval Training in Cardiac Rehabilitation. A REVIEW AND RECOMMENDATIONS. J Cardiopulm Rehabil Prev. 2021.

Acknowledgements: We would like to thank the participants involved in the study and the funders: The Swedish Rheumatism Association, The Norrbacka-Eugenia Foundation, and Stig Thunes´ Foundation.

Disclosure of Interests: None declared.

© The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.