Can salivary testosterone and cortisol reactivity to a mid-week stress test discriminate a match outcome during international rugby union competition?

Abstract

<p><i>Objectives:</i> Evidence suggests that stress-induced changes in testosterone and cortisol are related to future competitive behaviours and team-sport outcomes. Therefore, we examined whether salivary testosterone and cortisol reactivity to a mid-week stress test can discriminate a match outcome in international rugby union competition.</p><p> <i>Design:</i> Single group, quasi-experimental design with repeated measures.</p><p> <i>Method:</i> Thirty-three male rugby players completed a standardised stress test three or four days before seven international matches. Stress testing involved seven minutes of shuttle runs (2 ×20 m), dispersed across one-minute stages with increasing speeds. Salivary testosterone and cortisol were measured in the morning, along with delta changes from morning to pre-test (Morn-Pre Δ) and pre-test to post-test (Pre-Post Δ). Data were compared across wins (n = 3) and losses (n = 4).</p><p> <i>Results:</i> The Morn-Pre Δ in cortisol increased before winning and decreased prior to losing (<i>p</i> < 0.001), with a large effect size difference (<i>d</i> = 1.6, 90% CI 1.3–1.9). Testosterone decreased significantly across the same period, irrespective of the match outcome. The Morn-Pre Δ in testosterone and cortisol, plus the Pre-Post Δ in testosterone, all predicted a match outcome (<i>p</i> ≤ 0.01). The final model showed good diagnostic accuracy (72%) with cortisol as the main contributor.</p><p> <i>Conclusions:</i> The salivary testosterone and cortisol responses to mid-week testing showed an ability to discriminate a rugby match outcome over a limited number of games. The Morn-Pre Δ in cortisol was the strongest diagnostic biomarker. This model may provide a unique format to assess team readiness or recovery between competitions, especially with the emergence of rapid hormonal testing.</p>