CORTISOL, STRESS AND ADAPTATION DURING EXERCISE

CORTISOL, STRESS AND ADAPTATION DURING EXERCISE TRAINING
Journal: "Education. Physical Training. Sport"
Antony C. Hackney, Claudio Battaglini, Elizabeth S. Evans;
University of North Carolina, USA

ABSTRACT
Cortisol is a corticosteroid hormone produced by the zona fasciculata of the adrenal cortex in the adrenal gland. It plays vital roles in the bodyfs defense mechanisms when dealing with stress, as well as being important in blood glucose regulation. Regrettably, misconceptions regarding the actions of this hormone have been created around the sports and exercise arena. For example, cortisol most often is viewed as having a counter-productive role in exercise that can lead to a mal-adaptation to the exercise training process, due to the catabolic nature of this hormone with respect to protein turnover. Therefore, the intent of this article is to present an overview and to offer commentary on the necessary and critically important functions of cortisol during exercise, and in the adaptation process associated with exercise training. This is being done to specifi cally correct several of the misconceptions and misunderstandings that are portrayed within some literature (in particular on the Internet) regarding endocrine responses to exercise and exercise training.Stress has been a topic of study for over 100 years. It is well accepted that the paramount early leader in such study was Hans Selye. Classic observations and studies by Selye during the early part of the last century lead to the development of the gGeneral Adaptation Syndromeh theory of stress response (Selye, 1950). This theory proposes an intimate involvement of the adrenal gland, specifi cally the cortex, in the adaptation and mal-adaptation process to all forms of stress. Exercise and the exercise training process are classified as a stress to the human body (Hackney, 2006). Specifically, for sedentary individuals, exercise is a distress (negative), but as the body accommodates and adapts, exercise transitions to a eustress (positive) (Selye, 1950; Viru, 1976; Hackney, 2006). Selye viewed the adrenal cortex response (i. e., in humans the primary adrenal cortex hormone is the glucocorticoid cortisol) as critical to the positive adaptation to stress.The view by some exercise specialists that increases in cortisol can lead to a predominance of catabolism in the body which results in undesirable aspects within the adaptation of athletes in sports training is an over-simplifi cation of the hormonal rolesactions of cortisol. This simplified and incomplete notion regarding the role-action of cortisol during exercise training has even resulted in the development of nutritional-pharmaceutical supplements and dietary strategies which attempt to suppress cortisol levels at rest and in response to exercise(Duclos et al., 2007; Viru A., Viru M, 2001, 2004). Such actions may in fact actually compromise the ability of select physiological systems to respond and adapt to the stress of exercise.A. Viru and M. Viru (2004) report that this misconception of the role of cortisol seems rooted in the research focusing upon the testosterone/ cortisol ratio and how it changes in response to exercise training. In the 1980s, Adlercreutz and associates were the fi rst to focus attention on the testosterone/cortisol ratio, proposing its use as an indication of excessive stress in athletes during their training (Adlercreutz et al., 1986). These authors actually suggested the use of the ratio based upon free testosterone, not total testosterone, to cortisol. This latter fact seems to have been lost to some researchers who have calculated the ratio using the alternative testosterone value (Kuipers, Keizer, 1988; Viru A., Viru M., 2001, 2004).Cortisol plays such a role physiologically by stimulating several processes that are instrumental to increasing and / or maintaining blood glucose (i. e., euglycemia) (Bender, 1993; Brooks et al., 2005; Tortora, Derrickson, 2006). These processes include:œ Stimulation of gluconeogenesis particularly in hepatic tissue. This pathway results in thesynthesis of glucose from non-carbohydrate substrates such as amino acids and glycerol from triglyceride breakdown.œ Enhancing the expression of enzymes involved in the gluconeogenesis pathway is a key metabolic function of glucocorticoids.œ Mobilization of amino acids from extra-hepatic tissues: These serve as substrates for gluconeogenesis (see later discussion on the free amino acid pool).œ Inhibition of glucose uptake in muscle and adipocytes as a glucose and glycogen sparing action.œ Stimulation of lipolysis in adipocytes. Glucocorticoids, specifically cortisol, are considered stress response hormones, which in an overly simplified view, are often portrayed as being entirely negative in their infl uence on physiological function. The glucocorticoids are in fact vital hormones in the normal physiological functioning of humans and are necessary in dealing with different stress challenges to the body. With respect to exercise, they play an important regulatory role in metabolic responses. Additionally, the regulation of protein turnover during the recovery from exercise, which is instrumental to the myo-plasticity response of skeletal muscle in training, is dependent upon appropriate glucocorticoid actions. In other words, cortisol and the other glucocorticoids are not the gbad guysh of exercise endocrinology as some have made them out to be. Researchers, athletes and sports coaches need to be aware and conscious of the critical nature of glucocorticoids to normal health and development, especially relative to exercise training adaptations.