Fig. 1: Heart rate monitoring, psychological testing and tau profiles in female soccer players in response to repetitive head impacts.

a Schematic illustration of the study protocol, sampling and analysis. b Monitoring of maximal heart rate revealed no difference between exercise and heading groups. Athletes performed exercise (E) with higher physical activity compared with heading (H + E) training, represented by the higher (c) mean heart rate and higher (d) percentage of maximal heart rate. e Both training sessions were associated with decreases of focused attention of athletes when compared to baseline (black dotted line) as assessed by the Trail Making Test A (TMT-A), while the worsening was higher in the heading group. f Heading session also showed negative outcomes on cognitive flexibility (TMT-B) of athletes compared to baseline and exercise. Psychological testing revealed that heading training was associated with worse cognitive abilities than exercise without repetitive headers. g Analysis of total tau, pTau₁₈₁ and pTau₂₁₇ in plasma revealed no significant difference between exercise and heading groups at baseline. Horizontal black lines denote the mean and 95% CI. h Significant increase in the fold change of plasma tau from baseline was observed in athletes 1 hour after both training sessions, while there was a significant difference between E and H + E training. The higher change in tau protein normalized to baseline (black dotted line) in the exercise group was significantly decreased in the heading group after 48 hours. Significant change in plasma (i) pTau₁₈₁ and (j) pTau₂₁₇ from baseline was observed 1 hour after both types of training. The increased change in phosphorylated tau protein normalized to baseline within 24 hours. k The ratio of pTau₁₈₁ to tau fold change was significantly higher 1 hour and 48 hours after heading when compared with exercise. Similar, yet nonsignificant increase of (l) pTau₂₁₇ to tau fold change ratio in the heading group was also observed. The color of the P value in (h-j) indicates within-group significance between baseline and corresponding time points, as per legend. The interaction between groups is indicated by lines and the corresponding P value in black color. Statistical significance (b-d) was assessed using the two-tailed Mann-Whitney test. Statistical significance (e-l) was assessed using the two-way ANOVA with Tukey’s multiple comparison test. Exercise group (n = 36), heading group (n = 30) in tau and pTau₁₈₁ analysis and both groups (n = 11) in pTau₂₁₇ analysis.