Cortisol
Cortisol is the primary member of a family of glucocorticoids, and is considered the main catabolic hormone. Corticosterone is the other glucocorticoid, but is thought to be much less potent than cortisol (accounting for approximately 4-5% of total glucocorticoid activity). Cortisol is made and secreted from the adrenal cortex, via the hypothalamic-pituitary-adrenal (HPA) axis, with a small amount also derived from the conversion of cortisone. The catabolic effects of cortisol can result in decreased protein synthesis and increased protein degradation. Chronically high cortisol levels have been linked to various stressors (trauma, depression, overtraining); thus, this glucocorticoid is also considered one of the primary stress hormones. In blood, greater than 90% of this hormone is bound with plasma proteins, mainly with cortisol binding globulin and the rest with albumin, with the remaining fraction circulating freely.
The amount of cortisol present in the serum undergoes diurnal (having a daily cycle or occuring everyday) variation, with the highest levels present in the early morning, and the lowest levels present late in the evening (generally 3-5 hours after going to sleep).
It has been shown that stress or disease-induced increases in plasma cortisol and corticosterone results in lower testosterone secretion from the testes. It has also been shown that cortisol downregulates IGF-1 mRNA levels, implying that some of the catabolic effects of glucocorticoids is due to reduced autocrine /paracrine expression of IGF-1.
Cortisol levels within normal ranges cause numerous actions which help restore homeostasis after stress. When cortisol levels are chronically high problems can occur.
Program Design
In general cortisol increases with increased duration of intense exercise. Hypertrophy lifting schemes cause a greater cortisol response than neuronal lifting schemes. A hypertrophy scheme performed among trained females revealed a much greater stress response than a neuronal scheme. Dynamic power schemes have also resulted in hyper cortisol levels, although not to the same extent as hypertrophy schemes. On average, dynamic power schemes have resulted in a 20% increase in blood cortisol whereas hypertrophy schemes have resulted in a 45% increase. Neuronal schemes have not produced any change in cortisol levels across exercise.
Some people suggest measuring testosterone/cortisol ratios can be used as an indicator for overtraining. According to this suggestion an elevated cortisol level in relation to testosterone suggests overtraining (overtraining is a word used too often in this industry. What is overtraining to one individual may not be to another. Different people define overtraining differently.). A study looking at endurance trained cyclists showed that decreased testosterone levels, increased cortisol levels, and a decreased testosterone to cortisol ratio does not automatically lead to a decrease in performance or overtraining. There are probably many high level athletes who have elevated cortisol and depressed testosterone that function fine. In my opinion the importance of the cortisol to testosterone ratio is overemphasized and is only one factor that should be considered when designing or evaluating athletes’ programs.