BACKGROUND/AIM: Injuries and health problems of soccer players may appear abruptly and are often unexpected. However, hypotheses from complex systems theory suggest that these events can be preceded by certain Early Warning Signals (EWSs).1 We tested whether injuries and health problems can be anticipated with a specific type of EWS, that is, an increase in dynamic complexity (DC).2METHODS:Over two competitive seasons, we collected psychological and physiological self-reports (i.e., self-efficacy, motivation, mood, rating of own performance, enjoyment, and recovery) and data from heart rate sensors on every training and match day from 14 youth soccer players. We recorded time-loss injuries daily and players filled in the Sports Trauma Research Center Questionnaire on Health Problems (OSTRC-H2) once a week. We then calculated the DC of the self-reports and sensor data in a seven-day window to test for increased variability and complexity over time before injuries and health problems.RESULTS:Players experienced 5.6 injuries and 8.4 health problems on average across two seasons (range=1-18 and range=2-26, respectively). Results showed that increases in DC could often anticipate the occurrence of injuries and health problems. In 55% and 37% of the players DC increased up to five days before injuries and health problems, respectively (SD=39% and SD=25%, Min=0% and Min=0%, Max=100% and Max=83%).CONCLUSIONS:Results of this study suggest that EWSs can be used for real-time anticipation of injuries and health problems in daily soccer practice. Future research should test for the robustness of these results within and between individuals and perform sensitivity and specificity tests. In addition, finding out how warning signals can be communicated to soccer players and staff is an interesting avenue.REFERENCES1. Den Hartigh RJR, Meerhoff LRA, Van Yperen NW, et al. Resilience in Sports: A Multidisciplinary, Dynamic, and Personalized Perspective. Int Rev Sport Exerc Psychol. 2022. doi:https://doi.org/10.1080/1750984X.2022.20397492. Olthof M, Hasselman F, Strunk G, et al. Critical Fluctuations as an Early-Warning Signal for Sudden Gains and Losses in Patients Receiving Psychotherapy for Mood Disorders. Clin Psychol Sci. 2020;8(1):25-35. doi:10.1177/2167702619865969<br/
