Background: The aim of this study was to analyse the salivary cortisol variations during a 30 min sub-maximal exercise, the load being fitted so that the heart rate remains constant at 170 +/- 4 bpm.
Methods: Tests were conducted at 10 a.m. precisely (in order to avoid circadian variations), and cortisol values were recorded every 5 mn by means of a sampling collector over 40 mn), (30 mn bout + 10 mn post-exercise) and then at 30 mn, 1 h 30 mn and 5 h following the end of the exercise. Test values were compared to reference values, (average cortisol resting levels obtained at comparable hours on a previous day). Nine sport-students, (5 boys, 4 girls) entered the study.
Results: The cortisol level presented a significant increase from the first step of the exercise and then, as opposed to an exercise where a constant load is applied, it did not keep increasing but remained steady until the end of the test. After stopping, a new significant increase surprisingly appeared; the values then dropped to reference levels, but they were still higher 1h 30 mn after exercise had stopped.
Conclusions: It appears that when the perceived stress of the body reaches an equilibrium, as controlled by monitoring the heart rate, cortisol levels quickly rise to a steady state, about two folds higher than resting values in our experimental conditions.