Does Cardiorespiratory Fitness Predict the Physiological and Psychological Stress Response to a Mathematics Exam in Secondary High School Students?

School is widely recognized as one of the primary sources of stress among adolescents. While some studies employing laboratory-based stressors have suggested that adolescents with better cardiorespiratory fitness (CRF) may exhibit lower stress reactivity to psychosocial stressors, research based on real-life stressors is lacking. Therefore, we examined whether CRF predicts physiological and psychological reactivity in response to a real-life stressor (mathematics exam). Students were recruited from Swiss public schools (9th grade). The final sample included 67 students (58% female, Mage = 15.09 years). Heart rate (HR), heart rate variability (HRV), mood states, and state anxiety were used as indicators stress reactivity. CRF was assessed using the 20m shuttle-run test. Statistical analyses used regression analyses, which were controlled for relevant social and demographic confounders, as well as baseline outcomes during a nonstress condition (normal mathematics lesson). Exposure to the mathematics exam resulted in decreased HRV and mood, alongside increased state anxiety. While better CRF was associated with lower HR, higher HRV, better mood, and lower state anxiety across stress and baseline conditions, CRF did not predict physiological and psychological outcomes after controlling for baseline scores and confounders. Hence, our study suggests that although better CRF is associated with favorable physiological and psychological states, this relationship appears independent of students' current stress exposure. Further research employing other ecologically valid stressors is needed to better understand the impact of CRF on real-life stress reactivity. From a school health perspective, it is essential to support students in developing the capacity to cope effectively with academic stressors.