Interleukin-6 and cortisol responses following a short- and long-term cycling test in team athletes with different cardiorespiratory fitness levels

This study investigated the effects of short- and long-term cycling exercise on salivary cortisol and IL-6 responses in team athletes with varying cardiorespiratory fitness levels. Twenty-seven athletes were categorized into three fitness groups based on estimated VO 2max : very poor/poor (V/P), fair/good (F/G), and excellent/superior (E/S). Participants completed two cycling tests in short-term (ST) maximal and long-term (LT) submaximal conditions, with saliva samples collected pre-exercise and at 0 and 30 min post-exercise to measure cortisol and IL-6 levels. Preliminary psychological assessments for anxiety and depression were also conducted. Findings showed no significant changes in cortisol levels across conditions or fitness groups ( p > 0.050). However, IL-6 levels increased significantly post-exercise in both ST (36% at post-0 and 116% at post-30) and LT (67% and 151%, respectively) conditions (time effect: F = 47.65, p < 0.001), with a more pronounced increase following LT cycling (condition effect: F = 9.22, p = 0.005). Notably, athletes with lower fitness (V/P) exhibited greater IL-6 responses compared to higher fitness groups (F/G and E/S) in both exercise conditions ( p < 0.050). Hierarchical regression analysis identified VO 2max as a significant negative predictor of cortisol (post-0: β=-0.765, p < 0.001) and IL-6 responses (post-0: β=-0.618, p = 0.001), explaining up to 45% and 42% of the variance, respectively. In conclusion, IL-6 responses to cycling exercise are influenced by exercise intensity and cardiorespiratory fitness, with long-term exercise eliciting stronger inflammatory responses, especially in less fit athletes. These results emphasize the importance of considering fitness levels when evaluating exercise-induced neuroimmune-endocrine responses and support individualized training programs tailored to optimize inflammatory and hormonal adaptations.