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High-Intensity Interval Training (HIIT) & Cortisol Creep: Is HIIT Bad for You?

  • 5 min read

by Matt Weik

HIIT and cortisol creep sound like an evil villain in a Marvel movie, but in reality, it’s just a fancy way of asking a question. HIIT stands for high-intensity interval training and what we want to explore in this article is whether or not it lowers cortisol levels.

Let’s first understand all aspects of HIIT and cortisol.

What is HIIT?

High-Intensity Interval Training (HIIT) is a form of cardio performed at a high intensity for a short duration with around an equally spaced rest phase. These sessions are typically in the 15-30 minute range, including the rest periods.

There are many different types of HIIT training: running, biking, rowing, swimming, and even lifting weights. The most common type of HIIT training is sprinting all out for 30-60 seconds, followed by active rest (slow jogging or walking).

In fact, many HIIT workouts will have you alternating between intense bursts of activity and fixed periods of less-intense activity or, in some cases, even complete rest. The benefit of this style is that you can get a great workout in less time than it would take to do moderate-intensity exercise.

How Does HIIT Work?

HIIT exercise pushes your body to its limits — then beyond — which forces it to adapt and get stronger. You recruit more muscle fibers during the exercise and get your heart rate higher than you would with traditional aerobic exercise.

And since HIIT increases the amount of oxygen your body uses during exercise, you can even increase your metabolism throughout the day. This means that you have the ability to continue burning calories long after your workout is over.

What is Cortisol?

Cortisol is a hormone produced in our adrenal glands, two small organs located on top of each kidney. Cortisol is part of a group of hormones called corticosteroids, which are produced by the cortex (outer part) of the adrenal glands.

Cortisol is often referred to as “the stress hormone” because it helps your body respond to stress, but it also plays many other important roles in your body.

What Do Cortisol Levels Do?

Cortisol works with certain parts of your brain to control your mood, motivation, and fear. It also works with the immune system to regulate inflammation. Cortisol also helps control blood sugar (glucose) levels and metabolism. In addition, cortisol can help manage salt and water balance in the body.

Cortisol affects many systems and parts of the body, including:

  • Immune system
  • Heart
  • Blood vessels
  • Digestion
  • Kidneys
  • Muscles
  • Bones

HIIT and Cortisol Creep

Before we get into whether HIIT is bad for you, let’s further discuss cortisol. Cortisol is also a catabolic hormone that can cause the breakdown of lean muscle tissue. An increase in cortisol can be induced by stress, lack of sleep, overtraining, and excessive exercise. Overall, cortisol has both good and bad properties depending on the levels and how long the hormone stays elevated.

Cortisol creep is when an athlete starts to notice an increase in their resting cortisol levels (during non-exercise periods) due to overtraining/excessive exercise. This is not a good thing because it can decrease performance, increase the risk of injury or illness, and lead to an increase in body fat storage. Cortisol can also cause a rise in a hunger hormone called ghrelin, which has the potential to cause you to overeat and gain weight.

In a nutshell, excessive exercise can increase resting cortisol levels, which can negatively affect your fitness goals and results.

Cortisol Creep Symptoms

The first symptoms of cortisol creep are usually hard to distinguish from your everyday life stress. How many times have you looked at your schedule and felt overwhelmed? You’re overbooked at work, the kids have soccer practice and ballet recitals, and you’re trying to squeeze in time with your spouse before the week starts again.

But if you recognize any of these additional symptoms, it’s likely that your body is trying to tell you that your workout routine is making more work for it than it can handle:

  • Unexplained weight gain (particularly around your waist without dietary changes)
  • Feeling lethargic during the day but wired when you climb into bed at night
  • Trouble falling asleep or staying asleep
  • Brain fog or lack of focus throughout the day
  • Irritability or the feeling of depression

When Should You Avoid HIIT?

If you are concerned about your adrenal health, it is important to avoid high-intensity interval training during times of high stress.

This includes times when you are feeling stressed out, as well as times when you are recovering from an illness, injury, or surgery. This is because these types of high-intensity interval training workouts can cause a massive spike in your cortisol levels and can make it harder for your body to heal and recover.

You should also avoid HIIT if you have any issues with your adrenal glands. This includes adrenal fatigue, high blood pressure, high blood sugar, diabetes, or if you have a family history of these conditions. Even if you do not currently have any issues with your adrenal glands or cortisol levels.

If you are pregnant or breastfeeding, it is also important to avoid HIIT workouts. These types of workouts can cause a spike in your cortisol levels and a drop in your blood sugar levels that may not be safe for your baby.