Fig. 2: Summary of digital biomarkers across conditions.

This figure offers a visual overview of the digital biomarkers examined in relation to fatigue across various chronic health conditions discussed in this review. Each row shows a specific digital biomarker (e.g., daily step count, HRV, sleep efficiency), while each column represents a different chronic condition. Green bubbles show that the biomarker has been studied in that condition, whereas red bubbles indicate it has not. This chart highlights both established research areas and gaps in current knowledge, providing insights into where future studies are needed to better understand the role of digital biomarkers in fatigue assessment and management. Abbreviations: MS, multiple sclerosis; RA, rheumatoid arthritis; COPD, chronic obstructive pulmonary disease; CFS, chronic fatigue syndrome; IBD, inflammatory bowel disease; PSS, primary Sjogren’s syndrome; SLE, systemic lupus erythematosus; PD, Parkinson’s disease; HRV, heart rate variability; MVPA, moderate-to-vigorous physical activity.