The effects of cortisol on training adaptations

The effects of cortisol on training adaptations

While the intention behind physical activity is noble, the physiological stress generated by training also leads to the release of cortisol.

By Pierre-Luc Dubé


Today’s society is performance driven. Whether at work, at home or in sport, the people who stand out are often the ones who are admired. With performance comes pressure and stress. This state of mind can translate into physical symptoms and influence the normal functioning of the human body on a cellular level. Training is, under the same principle, a disturbance that the body must face. While the intention behind physical activity is noble, the physiological stress generated by training also leads to the release of cortisol, a catabolic hormone involved in the so-called “fight-flight” response. The control of its concentration in the body is one of the aspects that significantly influences the implementation of the adaptations generated by training. This hormone is still necessary in order to disrupt the cellular environment and induce adaptations but can interfere with the goals of building muscle mass and improving body composition when it is found in too great a concentration.

The primary goal of training is to promote muscular and physiological adaptations by establishing greater or lesser fatigue. However, too much fatigue drastically increases cortisol levels and prolongs recovery time. It then becomes important to quantify the level of fatigue caused by training in order to have optimal concentration. The presence of too high a level of the hormone prevents the body from going into recovery mode and replenishing its energy reserves. Maintaining the mobilization of stored ressources found inside the muscle, such as muscle glycogen, can help reduce muscle size. Muscle, being an important reserve of carbohydrates, sees its saturation reduced when stress, or at least the perception of stress, persists over a long period of time. The low level of substrates inside the muscles then limits the energy potential available and necessary for muscle contraction. In addition, the catabolic effect of cortisol may influence hormonal secretion. The level of testosterone circulating in the body can be reduced by too much cortisol concentration.

On the other side of the continuum, improvement in body composition, and more specifically the amount of fat in an individual, is also influenced by the presence of cortisol. It thus limits the level of conversion of thyroid hormones T4 (low activity form) into T3 (active form). This results in a slower metabolism and greater storage of energy resources in the form of fat. In addition, cortisol, being inflammatory, gives the impression of being more fatty and promotes the deposition of fat mass in the abdomen. Another problem that comes with having too much cortisol over too long a period of time is insulin resistance. In response to the rise in blood sugar caused by the mobilization of energy reserves, the body somehow becomes lazy and does not respond as well to the presence of carbohydrates. Having a poor ability to cope with rising blood sugar levels, the body promotes storage instead of using sugars for energy production.

With the physiological system having no eyes, it is difficult to predict the perceived intensity of stress. The body secretes cortisol in order to cope with the stress it is subjected to, sometimes in an exaggerated way depending on the context. Beyond training, the external stress that comes with everyday life can also add to and modulate our hormonal response. It becomes even more important to prescribe the right types of workouts and volume for our clients to minimize the increase in cortisol. However, we must keep in mind that it is necessary in order to generate muscular and physiological adaptations. It is rather chronic exposure to too much cortisol that can become problematic and affect clients’ physiological functions.


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