With all the benefits that exercise offers, it still places short-term stress on your body, but, in moderation, it’s a “healthy kind of stress. In fact, the stress of exercise forces your body to adapt and become stronger. Plus, with cardiovascular exercise, you develop greater stamina and endurance. That’s important for your long-term health, well-being, and functionality.
Behind the scenes of a workout, your body releases a barrage of hormones. Studies show that exercise stimulates the release of stress hormones, including cortisol and adrenaline, and the effects depend upon the type of exercise, exercise intensity and duration, and other factors such as pre-workout fuel status and sleep the night before.
Even the time of day that you exercise can affect stress hormones, particularly cortisol since cortisol follows a circadian rhythm and 24-hour cycle. Let’s look more closely at how exercise changes the body’s stress response and stress hormones.
Adrenaline is sometimes called the “fight of flight” hormone because your adrenal glands, specifically the adrenal medulla, produce more of this activating hormone during times of stress to give you a burst of energy to fight or flee a predator. It also boosts your heart and increases blood flow to your skeletal muscle to help you mobilize quickly. Plus, a study in mice found that adrenaline mobilizes natural killer cells, cells that protect against viruses and malignant tumors.
Although designed for escaping predators, we have fewer predators to escape from these days, so most people get their adrenaline surge from exercise. Adrenaline is the hormone that increases your heart rate and mobilizes glycogen and fat stores to supply your muscles with a substrate to make ATP to fuel exercise. There are stories of people who manifested almost impossible displays of strength when forced to, thanks to the power of adrenaline. For example, brave folks who lifted a car to save someone trapped underneath.
As you might expect, you release more adrenaline during more intense workouts, but intensity matters. A 1984 study found there was little or no increase in adrenaline in response to mild-to-moderate exercise. It’s during intense exercise, like high-intensity interval training, that you get significant adrenaline release.
Another close cousin of adrenaline called noradrenaline also goes up during exercise. It has a similar function as adrenaline; it increases heart rate and blood flow to working muscles. It also helps mobilize energy stores, including glycogen and stored fats to supply more energy to muscles.
The increase in adrenaline and noradrenaline during exercise is greatest in people who don’t exercise regularly. After training for a while, your body adapts and the boost in these two stress hormones diminishes somewhat. So, you’ll get the biggest adrenaline boost when you first start working out or when you increase the intensity of your workouts.
Cortisol is another hormone that your adrenal glands produce in response to stress, but it’s the adrenal cortex rather than the adrenal medulla that manufactures and releases cortisol into the bloodstream. It’s not just exercise that boosts cortisol release; chronic mental stress, restrictive dieting, low blood sugar, and lack of sleep can also cause a rise in the stress hormone cortisol.
Like adrenaline, the purpose of cortisol release during exercise is to supply your body with a source of fuel. Like adrenaline, it helps mobilize glycogen, fat stores, and, under conditions of starvation, protein your body can use as a fuel source. Since high-intensity exercise is more stressful and requires more fuel to sustain, cortisol levels rise more as exercise intensity goes up. But duration also affects cortisol release. At the same exercise intensity, cortisol rises more with longer duration exercise than with short workouts. For example, long-distance running will lead to a sharper rise in cortisol than running around the block.
Cortisol doesn’t do your physique any favors. It mobilizes energy stores your muscles can use to make ATP to fuel muscle contractions but has negative effects on body composition when it stays elevated for too long. High cortisol increases muscle protein breakdown, leading to muscle loss, and reduces muscle protein synthesis in response to strength training. It also suppresses immune function and boosts bone loss. If your cortisol level stays elevated, you can develop increased abdominal fat due to fat redistribution from the hips and thighs to the waist and tummy. This type of fat mobilization is especially unhealthy from a health standpoint.
It’s not surprising that athletes and bodybuilders try to suppress cortisol, so it won’t interfere with muscle development or lead to muscle loss. Some take supplements to suppress cortisol, including supplements that contain glutamine or phosphatidylserine. However, it’s best to avoid the cortisol effect by not overexercising, giving your body enough rest and recovery time, and by consuming enough calories and carbohydrates to supply your body with energy and good nutrition.
Exercise timing may affect the cortisol response too. Normally, cortisol is highest upon awakening in the morning and gradually drops as the day goes on, reaching a nadir in the evening. If you exercise first thing in the morning, the stress of exercise may raise your cortisol further and elicit more of a catabolic response, including muscle breakdown. One way to avoid this is to eat a healthy breakfast before a workout. The worst approach for taming cortisol is to work out in the morning after drinking only coffee. Caffeine can boost cortisol release even more. Combine that with a high-intensity workout and low carbohydrates, and the catabolic effects will be even greater.
The Bottom Line
Now you know how the stress of exercise affects stress hormones. You can reduce the cortisol response by eating something before a workout and having a snack that contains carbohydrates afterward. Give your body enough time to recover after each workout and make sure that you get at least seven hours of sleep per night since lack of sleep can raise cortisol. Balance exercise with rest and recovery and you’ll reduce the negative effects of stress hormones on your body.
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