For decades there has been a rather baseless theory floating around bodybuilding subculture that lifting weights intensely for longer than 1 hour/60 minutes will cause the body to release an exorbitant amount of cortisol and thus catabolize all your precious muscle tissue. Notice how these arbitrary numbers are always nice and round, just like the other myth that you can’t digest more than 50 grams of protein per feeding (don’t believe me, read this). But I digress…
Back on topic, cortisol may in fact be a “stress” hormone, but that doesn’t necessarily make it the villain and root of all evil when it comes to improving body composition. In fact we will touch on a few studies herein that show linear correlation between cortisol levels and lean body mass gains in resistance-trained individuals.
While stress is not always a good thing, the human body would be quite defunct without some stress. So read on as we cover what cortisol is, why and when we produce it, and why it isn’t the enemy for those who enjoy intense weight training for more than one hour at a time.
Cortisol—the “stress” hormone
Many people are likely to associate cortisol with stress since it is released by the adrenal glands in humans as a part of the autonomic nervous system’s fight-or-flight response. Cortisol belongs to a class of hormones known as glucocorticoids, which play a variety of roles in vertebrates; some of these effects are positive while others are a bit more debilitating.
Why cortisol matters for body composition
The main effects of cortisol we are concerned with when it comes to body composition are its role in metabolism and immune system regulation. When the body is in a food-deprived/fasted state, cortisol release acts to elevate blood glucose to a nominal range via gluconeogenesis.
Moreover, cortisol stimulates lipolysis, which is a prerequisite to fatty acid oxidation and ultimately body fat loss. In fact, several studies have shown that medium and high doses of synthetic glucocorticoids (like hydrocortisone and prednisolone) have significant bearing on visceral and total body fat loss. [1,2]
So from these preceding two points it would seem like the more cortisol, the better, right (especially for fat loss)? But not so fast, as with most things, cortisol is not without potential dangers when excreted in excess.
One such danger is that cortisol antagonizes the immune system and acts as an anti-inflammatory agent (that is to say that cortisol production increases as inflammation increases, which is an immunosuppressive process). Chronically elevated endogenous cortisol production also poses metabolic risks such as impaired insulin response (i.e. insulin resistance), cardiovascular risks such as elevated blood pressure and LDL cholesterol, mental health risks such as depression and anxiety, and bone health risks such as osteoporosis. [3,4,5]
Cortisol and resistance training
So we can see that cortisol is quite the double-edged sword, especially if you are looking to improve your physique and overall health. At this point you’re probably weighing the benefits of cortisol and the drawbacks that I just listed and thinking, “Do I really want to have all those nasty side effects just to improve my body composition?”
Well, the good news in the case of active gym-goers, is that the stress/cortisol release to resistance training is a form of “eustress” (positive stress), and consistent, diligent exercise will actually promote an attenuation of cortisol release to distress (negative stress) at other times of the day.
Like many other physiological responses to weight training, it is imperative that you step back and take a look at the big picture rather than just be concerned about acute effects of exercise. Most people fear training for longer than an hour as this will greatly increase cortisol and lead to muscle breakdown.
The reasoning for this has theoretical value but lacks much, if any, supporting research. Yes, intense resistance training for long periods of time (2-3+ hours) will cause cortisol levels to increase, which may acutely increase proteolysis and inhibit glucose uptake into skeletal muscle, but the long-term ramifications of this acute response appear insignificant and as noted before, the cortisol response to resistance training is actually linearly correlated with lean body mass gains (over an extended period of time).[7,8]
Ultimately, if you’re actually training “intensely” the odds are you won’t last much longer than 2-3 hours in the gym anyway. I could see cortisol response being an issue if someone is training for 4-5 hours at a time for weeks on end, but that’s not really cortisol’s fault; that’s an issue of not having a life (seriously, go do something else for a few hours). That being said, if you are one who’s a bit slower in the gym and has the time to spend a few hours hoisting barbells around then by all means go for it, the longitudinal effects of cortisol are not going to hamper you much if at all and may actually be in your benefit.
1) Babikian LG. Effect of Hydrocortisone, Corticosterone, and Cortisone on Visceral and Total Body Fat in Albino Mice Physiological Zoology. 1962; 35(4):314-322.
2) Arlettaz A, Portier H, Lecoq AM, Rieth N, De Ceaurriz J, Collomp K. Effects of short-term prednisolone intake during submaximal exercise. Med Sci Sports Exerc. 2007 Sep;39(9):1672-8
3) BILLER, B. M., SAXE, V., HERZOG, D. B., ROSENTHAL, D. I., HOLZMAN, S., & KLIBANSKI, A. (1989). Mechanisms of osteoporosis in adult and adolescent women with anorexia nervosa. Journal of Clinical Endocrinology & Metabolism,68(3), 548-554.
4) Fraser, R., Ingram, M. C., Anderson, N. H., Morrison, C., Davies, E., & Connell, J. M. (1999). Cortisol effects on body mass, blood pressure, and cholesterol in the general population. Hypertension, 33(6), 1364-1368.
5) Brown, E. S., Varghese, F. P., & McEwen, B. S. (2004). Association of depression with medical illness: does cortisol play a role?. Biological psychiatry, 55(1), 1-9.
6) Kraemer, W. J., Staron, R. S., Hagerman, F. C., Hikida, R. S., Fry, A. C., Gordon, S. E., ... & Häkkinen, K. (1998). The effects of short-term resistance training on endocrine function in men and women. European journal of applied physiology and occupational physiology, 78(1), 69-76.
7) West, D. W., & Phillips, S. M. (2012). Associations of exercise-induced hormone profiles and gains in strength and hypertrophy in a large cohort after weight training. European journal of applied physiology, 112(7), 2693-2702.
8) Simmons, P. S., Miles, J. M., Gerich, J. E., & Haymond, M. W. (1984). Increased proteolysis. An effect of increases in plasma cortisol within the physiologic range. Journal of Clinical Investigation, 73(2), 412.