Salivary Cortisol Measurement in Runners

Sample collections and salivary cortisol concentration measurements were performed according to a previous study^{16 (link)}. The runners were not allowed to brush their teeth, chew gum, or consume any food or drink except water, 15 min before the sample collection. Saliva samples were collected using Salivette^® cotton swabs (Sarstedt, Nümbrecht, Germany), centrifuged (1,500 × g) at 4 °C for 10 min, then immediately stored at − 80 °C until analysis. ECLIA measurements of salivary cortisol concentrations were performed using the Elecsys Cortisol II on the Cobas 8000 system (Roche Diagnostics K.K, Tokyo, Japan)^{15 (link),16 (link)}. The intra- and inter-assay coefficients of variation for salivary cortisol were 4.1% and 4.6%, respectively. The rate of change in the salivary cortisol concentration by exercise was calculated as the salivary cortisol concentration after exercise divided by the salivary cortisol concentration before exercise (%)^{16 (link)}.