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Are You Harming Your Body with too Much HIIT?

We’ve all heard of HIIT workouts. You’ve probably even done a HIIT workout or two. High-intensity interval training workouts are known to make a big impact in a short amount of time.


But while the benefits of HIIT may make you want to do it every day, experts say you should not. Doing too much HIIT per week can actually cause more harm than good. Keep reading to learn more about how to integrate time for recovery into your workout routine and prevent the harmful effects of too much HIIT.

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What is HIIT?


HIIT stands for High-Intensity Interval Training, a type of workout that consists of short bouts of intense work followed by a period of active recovery. The high-intensity segment usually lasts from 10-60 seconds, with the active rest portion lasting the same amount of time or longer. In a HIIT workout, you usually repeat the cycle of hard work and recovery around 3-10 times depending on the workout.


HIIT workouts have become increasingly popular over the last several years due to the many physiological benefits. Some of the benefits include:

  • Increased fat burning → HIIT has been proven to help to reduce body fat despite the relatively short time spent working out. However, HIIT is most effective for fat loss in people who are overweight or obese.

  • Calorie burning after the workout ends → Several studies have demonstrated that HIIT can increase your metabolic rate for hours after you finish the workout. HIIT has also been demonstrated to increase your metabolism after exercise more than weight training or jogging.

  • Increase muscle building → For many people, doing a HIIT workout will help to increase muscle mass. These increases in muscle mass are more likely to happen in people who were less active in the first place, which makes HIIT a great workout for beginners.

  • Reduced blood pressure and heart rate → Several studies have demonstrated that HIIT can reduce heart rate and blood pressure in people who are overweight or obese. Some researchers have also found that HIIT can reduce blood pressure more than the frequently recommended moderate-intensity exercise.

  • Improved oxygen consumption → Oxygen consumption refers to your muscles’ ability to use oxygen, and is typically increased using endurance training. However, HIIT manages to produce the same results in a much shorter time than traditional endurance training.

  • Reduced blood sugar → HIIT programs that last less than 12 weeks have been found to reduce blood sugar. A summary of 50 studies determined that HIIT workouts can also improve insulin resistance more than traditional exercise.

  • Improved aerobic and anaerobic performance → HIIT has been found to improve performance in both anaerobic and aerobic performance! This means you will have better physical performance in any workout you decide to do.

  • HIIT is time-efficient → Most of these workouts are around 15-30 minutes, yet they have been found to have the same effects as much longer workouts. One study found that cycling for 40-60 minutes 5 times a week had similar results in weight loss as a 12 minute HIIT workout performed only 3 times a week.

  • Improved heart health → Because HIIT increased pressure demand on the blood vessels in your heart, it also gives your heart a workout of its own. HIIT has also been found to increase the elasticity and flexibility of arteries and veins better than continuous aerobic exercise. One study also found that HIIT is easier n the heart for people with coronary artery disease.

Another factor behind the popularity of HIIT is that it's easy to see results! Most people see results in only several weeks. You also leave HIIT workouts with great feelings of productivity, energy, and power. This is due to the hormone cortisol. HIIT workouts notoriously release cortisol as you workout, which is partially why you see so many benefits. However, without proper recovery, this cortisol has nowhere to go and can actually harm the body.


Cortisol 101:


Cortisol is best known for being your stress hormone. It plays a primary role in your body’s fight or flight response and stress response. But cortisol’s job doesn’t stop at stress, cortisol actually serves many different roles in your body. Cortisol is released as part of the daily hormone cycle. Cortisol levels are highest in the morning when you wake up and lowest at night when you’re about to go to sleep. Cortisol plays a role in:

  • Blood pressure regulation

  • Glucose metabolism

  • Immune function

  • Inflammatory response

  • Insulin resistance

When your body has just the right amount of cortisol, it functions like a well-oiled machine. However, when your cortisol levels become heightened for too long, that is where problems begin to arise.


HIIT & cortisol:


Part of why HIIT is such an effective form of physical activity is due to the cortisol released throughout the workout.


When you spur your body to perform intense exercise like during a HIIT workout, cortisol is released into your bloodstream. As you push your muscles to work harder than ever, your brain receives the message that your survival depends on this interval. At this point, cortisol and other hormones are released, activating your sympathetic nervous system response.


The body will then make metabolic improvements following the workout and hormone release.


The cortisol creep:


The problem with cortisol arises when your body has too much of it. This can be caused by either physical or psychological stress. Cortisol can float around the bloodstream, causing negative symptoms throughout your body. Doing too many HIIT workouts per week is known to cause heightened cortisol levels.


Look out for the following symptoms that could mean your cortisol levels are creeping up:

  • Changes in mood

  • Sleeplessness or changes in sleep pattern

  • Chronic fatigue

  • Noticeable decrease in power while workout out

  • Anxiety

  • Repressed immune system or constant illness

  • Lack of physical and psychological motivation

  • Muscle fatigue

Any of these symptoms can be present at any time, even if you haven’t worked out in a couple days! They reveal that your body has been overly taxed by too much HIIT and an imbalance of cortisol.


Your body should know when to hit the pause button and slow cortisol release. But doing too much HIIT can confuse the brain, meaning it will potentially signal a protective response even during times of rest and relaxation. This means that even while doing everyday tasks, like driving to work or walking your dog can leave you feeling irritated. Your body is misinterpreting everyday stressors as life-threatening events worthy of a full-blown stress response. Because HIIT workouts stimulate such a powerful cortisol reaction, it’s critically important to prioritize recovery in between your high-intensity workouts.


Recovery 101:


You will not see positive physical results from your HIIT results without allowing your body proper time to rest and recover. On your rest days, your parasympathetic nervous system takes charge. In opposition to the sympathetic nervous system that ramps you up, the parasympathetic nervous system acts like the brakes on a car, slowing you down after the stressor has passed. Your parasympathetic nervous system sends your body into rest, digest, and recovery mode.


Some practices to make your recovery days more effective include:

  • Good nutrition

  • Yoga

  • Proper hydration

  • Quality sleep

  • Foam rolling

  • Massages

  • Keep away from intense exercise!


Without time for recovery, your body is stuck in a constant state of stress. This will cause the benefits of HIIT to reverse, with all your hard work now working against you. When you see any signs of stress in your body, take it as a hint to slow down and avoid HIIT for several days.


Ideally, you should only be doing HIIT workouts 2-3 times a week AT MOST, with proper rest days between each session. To make the benefits of your HIIT workout last, you must be aware of the physical and psychological signs of chronic stress in your body.



Trust us, we know it can be hard to not feel like you have to work out every day, and HIIT offers some very appealing benefits. But by doing so, you might actually be doing far more harm than good. Instead of stressing out over a workout, “healthify” your recipes to ensure you don’t get off track with your health goals this winter.


For more information, click here to contact us, or call 276-235-3205 to schedule your complimentary discovery call with Dr. Johnson.


The Johnson Center for Health services patients in-person in our Blacksburg and Virginia Beach / Norfolk locations. We also offer telemedicine for residents of Virginia and North Carolina!

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