A link between cortisol and performance: An exploratory case study of a tennis match

• Cortisol correlates with performance parameters in tennis.
• Methodological advancement by comparing winner & loser directly
• Methodological advancement by taking 20 cortisol samples per player within 3:35 h plus baseline
• Fluctuation of cortisol for the first time considered in psychoneuroendocrinological research

So far, studies have focused mainly on changes in cortisol levels before and after competitions, and little is known about cortisol secretion within a competition. In this exploratory study we aimed to gather in-depth information about cortisol development during a tennis match and to relate cortisol levels to specific performance parameters of two competitive male players. Thereby, we were also able to compare winner and loser directly. A total of 20 samples per player were assessed before (4 samples), during (10 samples), and after (6 samples) a match and on a resting day (5 samples). Cortisol was higher on competition day in comparison to resting day in both players. Further, cortisol was higher in the loser before (17%), during (65%), and after (54%) the match. In addition, cortisol was negatively correlated with certain performance parameters (e.g., unforced errors and return performance) but uncorrelated with other performance parameters such as serving performance. Further research should look into within-competition cortisol variations, additionally assessing different hormones, and take into account the methodological concerns that were identified in this single case study.