I only use it as a prospective index of the adrenal capacity in relation to stress (physical and mental). We did some small studies using an exercise test to stress a number of athletes. There is a clear trend at a lower cortisol response relativeto ACTH to physical stress in athletes with lasting declined performances. In this case, we use it as an indicator of the overtraining process.

Then, as the Testosterone/cortisol index when the index low is an indicator of the overtraining process?

No. Not like a ratio. I use the relationship between acth and cortisol. This fundamentally different from a simple ratio. We found this relation to be present in fit athletes with normal performance profiles. The relation may be absent after maximal exercise and /or in rest in athletes with worsened performance and increased negative mood profiles.

A temporal profile of ACTH and C ? Please tell us more Sandor, this is interesting.

Not sure what you mean with temporal Mark. As you know, corticosteroid receptors on the pituitary exist to regulate the production of ACTH. If you increase the sensitivity of these receptors, the increase of ACTH and hence the further increase of cortisol will be stopped very quickly, even if the system is stressed (production of CRH). This is what I saw in athletes suffering form long term performance drops and mood distutbances. My colleague Meeusen suggested a similar explanation when he studied a small group of athletes suffering from the overtraining syndrome while comparing them with athletes supposedly suffering form non-functional overreaching. If you like I can send you the details.