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Introduction: Regular physical activity is a key non-pharmacological component in the management of rheumatic diseases, yet long-term adherence remains challenging [1]. Wearable-integrated digital therapeutics may enable continuous monitoring of physical activity and physiological responses, providing objective digital biomarkers for personalized exercise therapy [2]. Our objective is to evaluate feasibility, usability, baseline clinical characteristics, and exploratory wearable-derived digital biomarkers in rheumatic patients using the Rheuma-Fit application with smartwatch integration.

Methods: Adult SpA patients used Rheuma-Fit over approximately three months. Baseline characteristics were collected via entry questionnaire. Usability was assessed using the System Usability Scale (SUS). Patient-reported outcomes included FACIT-Fatigue, HAQ, SF-36, and TSK. Continuous smartwatch data (heart rate and step counts) were processed, quality-checked, aggregated to hourly intervals, and analyzed descriptively for coverage, variability, circadian patterns, and heart rate–step correlations.

Results: Twenty-four patients were included at baseline (63% female; mean age 49.6±10.4 years; BMI 28.8±7.9 kg/m²). Moderate to severe fatigue was frequent (FACIT), and HAQ indicated minimal to moderate functional impairment with domain heterogeneity. SF-36 showed marked interindividual variability across physical and mental components. Usability was overall acceptable (SUS 45–100), with several “excellent” or “best imaginable” ratings. TSK scores (19–49) reflected heterogeneous kinesiophobia. Wearable data demonstrated prolonged monitoring (up to >2,200 hours/user). Mean heart rate ranged ~70–100 bpm, with substantial variability in hourly step counts. Heart rate–step correlations were consistently positive but individually variable, indicating differing exercise intensity patterns. Circadian heart rate profiles were physiologically plausible, supporting good wear-time adherence.

Conclusion: Rheuma-Fit with wearable integration is feasible in rheumatic patienst and achieves acceptable usability in most users, despite marked interindividual variability. Continuous digital biomarkers, including step-derived activity levels, heart rate dynamics, and circadian profiles, capture meaningful heterogeneity in physical behavior and physiological response. These findings support the potential of wearable-derived digital biomarkers to inform personalized, data-driven exercise interventions in rheumatic patients and justify larger controlled studies to evaluate clinical effectiveness and the prognostic value of digital biomarkers in personalized exercise therapy.

Disclosures: The authors thank all participating patients and the whole team of Medizinische Klinik 3 for their support of this project. This work was partially supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – SFB 1483 – Project-ID 442419336 and the Horizon Health 2022 project SPIDeRR (project code 101080711).

References

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[2] Knitza J, Gupta L, Hügle T. Rheumatology in the digital health era: status quo and quo vadis? Nat Rev Rheumatol. 2024 Dec;20(12):747-759. DOI: 10.1038/s41584-024-01177-7