Evidence check: Cortisol in the context of Sport

Cortisol is frequently discussed in sports contexts as a marker of stress, recovery, and overtraining. However, the evidence for actionable insights from single measurements (e.g., saliva or blood) is limited. Cortisol levels fluctuate strongly with circadian rhythm, diet, and individual variation. Single-point measurements are therefore unreliable. Longitudinal trends under controlled conditions may provide some guidance, but the evidence base is largely mechanistic. Consumer tests claiming an 'optimal cortisol window' are often overhyped. It is more practical to monitor sleep quality, training load, and subjective well-being. Caveat: Do not use such tests to diagnose adrenal fatigue or Cushing syndrome – medical evaluation is required.