IL-6 and Cortisol Responses to Cycling Exercise

Overview

This study aimed to investigate salivary interleukin-6 (IL-6) and cortisol responses following short-term and long-term cycling exercise in team athletes with different cardiorespiratory fitness levels. Participants completed a Wingate anaerobic cycling test and a YMCA submaximal cycling test in a randomized crossover design separated by a seven-day washout period. Saliva samples were collected before exercise, immediately after exercise, and 30 minutes after exercise to determine IL-6 and cortisol concentrations. The study also examined whether cardiorespiratory fitness level influenced the magnitude of these physiological responses.

Exercise-induced physiological stress activates numerous neuroendocrine and inflammatory pathways, including the hypothalamic-pituitary-adrenal axis and cytokine-mediated responses. Cortisol and interleukin-6 (IL-6) are among the most commonly investigated biomarkers of exercise stress and adaptation. However, the influence of cardiorespiratory fitness on acute hormonal and inflammatory responses to exercise remains incompletely understood. This study employed a randomized crossover design involving team athletes aged 18-35 years. Participants completed two cycling exercise protocols: a short-term anaerobic test (Wingate) and a long-term aerobic test (YMCA submaximal cycling test). The two testing sessions were separated by a seven-day washout period and were performed at the same time of day to minimize circadian variation. Saliva samples were collected before exercise, immediately after exercise, and 30 minutes post-exercise. Salivary IL-6 and cortisol concentrations were analyzed to determine acute physiological responses to both exercise modalities. Participants were categorized according to cardiorespiratory fitness level based on estimated VO₂max values, and biomarker responses were compared between fitness groups.