Salivary cortisol response to a 30 mn submaximal test adjusted to a constant heart rate

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.

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.

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.

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.