Can Cortisol Sabotage Your Muscle Growth?


Can Cortisol Sabotage Your Muscle Growth?

How your body responds to fitness training has to do with hormones – and how you train, of course. You hear a lot about anabolic hormones, like testosterone and growth hormone. These hormones help you build lean body mass by increasing muscle protein synthesis. You also may have heard about another hormone called cortisol. Most serious bodybuilders who want to build lean body mass are out to boost testosterone and reduce cortisol – but why? Can too much cortisol really sabotage muscle growth?

Cortisol Serves a Useful Purpose

As much as cortisol is demonized, you need this much-maligned hormone to sustain life. Cortisol is a type of steroid hormone called a glucocorticoid. It’s cortisol’s job to make sure vital organs like your brain, which uses about 20% of the energy your body produces, gets enough glucose. Cortisol is produced by two small glands located just above your kidneys called the adrenal cortex.

What would happen if these hardworking glands couldn’t churn out enough cortisol? If you fasted for a period of time, your blood sugar could drop to low levels in the absence of sufficient cortisol. Cortisol also helps regulate salt and fluid balance as well as blood pressure. If you were deficient, you might become lightheaded or dizzy when you get up quickly if your cortisol level is too low. Having a very low cortisol level isn’t healthy either. People with a disease called Addison’s disease don’t produce enough cortisol and are at risk of dying.

Cortisol Really is Catabolic

So, why does cortisol, a hormone your body needs, have such a bad reputation? After all, it helps ensure your brain gets enough glucose. The bad name it carries among bodybuilders has to do with HOW it keeps your blood sugar steady. When your blood sugar drops too low, your adrenal glands produce more cortisol. The cortisol these glands make breaks down muscle tissue and send the amino acids to your liver. Here, your liver turns those amino acids into glucose by a process called gluconeogenesis. Therefore, cortisol is stealing from your muscles to keep your blood sugar up. Now you see why cortisol is called a catabolic hormone.

Your cortisol level can rise in response to exercise training as well. Two factors affect the release of cortisol: exercise intensity and duration. Whereas low-intensity exercise doesn’t increase cortisol and actually seems to lower it. However, as the exercise intensity goes up, cortisol release rises. Duration is another factor. Long periods of exercise stimulate cortisol release. Makes sense since intense exercise and exercise of long duration is more stressful on your body and uses up more glucose. So, you can avoid a rise in cortisol by keeping intense workouts short and long workouts low in intensity. Still, even if you keep intense workouts brief, you’ll still get short-term cortisol release due to the stress of the workout. However, you’ll also get the release of anabolic hormones, like testosterone and growth hormone, to counteract some of the cortisol’s catabolic effects.

The reality is the short-term release of cortisol during or after an intense workout typically isn’t a problem. Such brief increases in cortisol don’t’ sabotage muscle growth since the elevation is short in duration. Plus, if the workout is intense, you also get the release of anabolic hormones to compensate. Where cortisol becomes a problem, in terms of muscle breakdown, is when it stays high long after your workout over.

Chronic Elevation of Cortisol

In contrast to the short-term release of cortisol in response to an intense workout, cortisol can stay elevated in some cases. This is particularly common in people who do longer periods of endurance exercise, like long-distance runners, who don’t consume enough carbohydrates and calories. Remember, one of cortisol’s main jobs is to maintain blood sugar and get enough glucose to the brain. Your brain truly is a glucose sucker.

Other reasons your cortisol can stay chronically high is if you’re dieting aggressively, consuming too much caffeine. It can also happen if you’re under physical or mental stress or not sleeping enough. That’s why it’s important to not over-train or cut your calories too low. It’s also important to have ways to manage stress and to make sure you’re getting at least seven hours of sleep a night. Research shows that severe overtraining can actually interfere with the ability of your adrenal glands to produce cortisol, leading to what alternative practitioners call adrenal fatigue.

Other Negative Effects of Elevated Cortisol 

When cortisol stays elevated over a sustained period of time, it does other sneaky things to your health. One thing it does is suppress your immune system. Marathon runners often get colds a week after their run. Part of that has to do with the elevation of cortisol making it harder to fight off infection. Your immune system needs the action of T-cells to keep viruses and bacteria in check. Cortisol interferes with the activity of these important infection fighters.

We already mentioned that chronically high cortisol leads to loss of muscle tissue. It can also trigger fat redistribution, leading to greater fat storage around the waist, tummy, and upper body as opposed to the lower body. Though cortisol increases fatty breakdown short-term, chronic elevation can lead to weight gain, partially because cortisol increases cravings for sugar and fatty foods.

The take-home point? Cortisol sounds like a bad guy but it’s only problematic if it stays elevated for longer periods of time. The short-term increase you get in cortisol when you do an intense workout is self-limited and it’s offset by the surge in anabolic hormones intense workouts trigger. Also, you can bring your cortisol level down after a workout by eating a carb/protein snack with a ratio of about 3 to 1 carbs to protein. It’s sustained cortisol elevation that can sabotage muscle growth and lead to muscle loss.

The Bottom Line

Now you know how cortisol can impact muscle building and your health. The most important thing to remember is chronically elevated cortisol is what is problematic. You can keep your level down by fueling your workouts properly, not overtraining, getting enough sleep, and learning to manage stress. Those things will also help you best reach your fitness goals.



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J Nov Physiother. 2013 Feb 16; 3(125): 11717.doi:  10.4172/2165-7025.1000125.

Baechle TR & Earle RW. Essentials of Strength Training and Conditioning. National Strength Training Association, 2nd ed. Human Kinetics.

Psychoneuroendocrinology. 2001 Jan;26(1):37-49.

Dartmouth Undergraduate Journal of Science. “The Physiology of Stress: Cortisol and the Hypothalamic-Pituitary-Adrenal Axis”


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