Fig. 4

Correlation heatmap for study participants. Correlograms depicting Spearman’s correlation coefficients between biomarkers of endothelial function and inflammatory cytokines/chemokines status, and illness severity (assessed by self-reported outcome measures) of patients with ME/CFS (A), long COVID (B), and matched sedentary healthy controls (C) were illustrated using the Spearman’s rank correlation test and FDR-adjusted p-value < 0.05. Pairwise Spearman’s rank correlation coefficients (rho) are depicted for each correlation and represented by a color intensity scale (at the top left of each panel). Heat colors show standardized Z-scores (adjusted rho) across biomarkers and outcome measures. The color intensity is proportional to the strength of the association (rho-value), ranging from red (positive correlation) to blue (negative correlation). Significance was assessed using the Kruskal-Wallis test. FDR was calculated using the Benjamini-Hochberg method. Statistical significance level was set at *p < 0.05, **p < 0.01, and ***p < 0.001