Fig. 3

Methodological workflow for the identification of the good surrogates. This process was repeated for each HRV feature at each time scale. The complete list of feature computed at each time scale is reported in Table 1. p: p-value; trend analysis: ↓↓ (↑↑): significantly lower (higher) under stress (p < .05), ↓(↑) lower (higher) under stress (p > .05); rho: Spearman’s rank coefficient, prho: Spearman’s rank p-value