(A) Individual (left) and group mean (right) ccf-mtDNA1 (mt-ND1) responses to acute psychological stress at session 1. (B) Validation of the results in (A) in a repeat session 2 one month later. Arrow: a participant with unusually high mtDNA1 baseline values at both sessions. Data are means and SEM. Repeated measure ANOVA on log-transformed data and Least Significant Difference (LSD) pairwise comparisons, n = 31 per session, * P < 0.05, ** P < 0.01, *** P < 0.001, **** P < 0.0001.