Can HIIT Make You Sick? (Yes, Here’s Why & How To Avoid)

Can HIIT make you sick (yes, here's why & how to avoid)

Have you ever experienced times in your life when your body seems to be telling you something? Perhaps you’re getting plenty of sleep but just can’t seem to beat your fatigue. Maybe you have a nagging head or body pains. Or sometimes the sniffles just won’t go away.

As a nutrition professional and fitness fanatic, I’m constantly reevaluating the balance of something being healthy or too much of a good thing.

Recently, my guilty pleasure has been those oh so hip spin classes with candles, motivational words splayed across the walls, and heart-pumping tunes. These cult-like classes give a full-body workout, incorporating weights and high-intensity bouts mixed with endurance training.

Lately, I bumped my participation up from two to five times a week. However, after getting sick every couple of weeks, and eating my way through all the carbs and sweets (weight gain included), I realized I was HIITing it too hard.

So can HIIT training make you sick? Yes, HIIT can make you sick. Doing excessive intense exercise (like HIIT) more than 3-4 times per week, can weaken your immunity and make it easier for you to get sick. With that said, regular physical activity can boost your body’s natural defense mechanisms, helping to fight disease and prevent illness.  The key is to hone your recovery and not to overdo it.

In the interest of your immune system, let’s learn how to avoid the hit of sickness, from doing too much HIIT training.

Note: I want to make it clear that most people SHOULD be doing HIIT training. This article is for those people who think they might be doing too much, and therefore, lack proper recovery. Some of the best HIIT training sessions I’ve done are on the Fitbod app. The algorithm takes into account your current levels of fitness and recovery levels when programming your workout.

Related Article: Can You Do HIIT And Weight Training On The Same Day?

What is HIIT?

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Before we examine the ins and outs of your immunity, it’s important to know what HIIT is and how it impacts your body.

The acronym HIIT stands for high-intensity interval training. This type of exercise is known for its quick bursts of intense exercise, followed by a brief rest period

The intense portions typically last between 15 seconds and a few minutes. These give-it-all-you-got bouts are alternated with 20-30 second rest periods. In a typical HIIT workout, you’ll have anywhere from five to eight of these rounds.

During the intense exercise portions, the goal is to reach max effort. This causes your body to switch to an anaerobic (without oxygen) state.

As a result, your body will rely on other energy stores. It helps you burn fat, increases endurance training, and has a calorie burn effect that lasts beyond the workout.

There are different types of HIIT but they all offer health benefits within a short period of time. In fact, since HIIT is performed at max intensity, studies have shown that the perks are almost twice as much as moderate exercise.

So with all these benefits in such a short period of time, it seems logical that more is better, right? – not exactly.

Related Article: The Top 5 Cardio Machines That Are Good For Weight Loss

How HIIT Hits Immunity

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HIIT is a highly efficient exercise but just like most things, too much is not necessarily a good thing.

Health authority, Precision Nutrition, explains that intense exercise such as HIIT, puts your body into an “emergency mode” and elevates stress hormones.

When your body is working at 85-95% of V02Max (the max rate your heart, lungs, and muscles can use oxygen) hormones such as testosterone, adrenaline, noradrenaline, endorphins, and cortisol are increased.

Related Article: HIIT Upper Body Workout: Workouts With & Without Weights


Studies show that chronic stress has a detrimental effect on immune function. These factors make it so you’re at a higher risk for viruses, the common cold, and cold sores.

Chronic stress decreases:

  • NK (natural killer) cell activity: a type of lymphocyte (white blood cell) and part of the innate immune system (first line of defense against invading pathogens).

  • Lymphocyte populations: one type of white blood cell, working to fight illness and disease.

  • Antibody production: a blood protein that “tags” foreign substances that come into the blood in order to protect the body from their attack.

  • Defense against viral infections: with stress, a virus that has been in your body is reactivated, allowing it to spread.

High stress can also affect your mind, leading to depression and anxiety. Many studies show that moderate exercise can improve levels of anxiety and depression. But as MedlinePlus explains, pushing for too hard, for too long can increase anxiety, decrease motivation, and disrupt sleep.

Related Article: Should You Do Cardio On Rest Days?


After a good workout, you may notice that you’re sore a day or two afterward. When you lift weights, you create small tears in your muscle fibers. As a result, your body will have some short-term inflammation, which is a normal part of the process.

As long as there is adequate nutrition, hydration, and rest time, your body will build more muscle and heal properly.

But when you start to experience soreness, sharp pain, or longer-term aches and pains, it could be a sign of inflammation due to injury. Inflammation signs can also include feeling run down, tired, or stressed.

There is evidence that exercise can both cause and reduce inflammation. Intense exercise such as HIIT, is healthy in moderation but too much can cause chronic inflammation.

Chronic inflammation has been linked with chronic diseases such as arthritis, psoriasis, inflammatory bowel disease, heart disease, diabetes, cancers and cognitive decline.

Learn more about the “good” and “bad” kind of sore: Should You Do Cardio With Sore Muscles? (Yes, Here’s Why)


Moderate exercise can help protect you from illness, but training too long at high intensities can make you more vulnerable to a flu or common cold.

Studies suggest a theory is that intense exercise causes an “open window” of time (lasting between a few hours to a few days) in which your immunity is compromised.

If you repeat the exercise or training without enough recovery time, you may increase your risk of illness.

Meaning, if you do intense exercise such as HIIT on a daily basis, or for longer than 30 minutes at a time, you could be decreasing your immunity and increasing your chances of getting sick.

Carbohydrate intake is one of the most effective ways to minimize these immune disturbances. Sleep is al
so an important aspect of recovery but more research is needed to determine how sleep disruption influences the immune system of athletes.

Related Article: Beginner HIIT Treadmill Workout: Starting With HIIT Cardio

Should You Work Out When You’re Sick?

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So say you’ve been slaying your fitness routine and ended up catching a pesky cold. You want to stay and track and keep your hard-earned progress but you don’t know if exercising will make it worse.

With mild sickness, such as a slight cold or sniffly nose, you can start exercising once the symptoms are gone. In fact, easy or moderate sports may even have a positive effect.

But if you’re recovering from something a bit more severe such as a flu, fever or infection that you had to take antibiotics for, your immune system is most likely still compromised. So lay off the exercise until you’re fully recovered and done with your course of antibiotics.

Take note that this is not the same recommendation for intense exercise such as HIIT. Since HIIT workouts impact the immune system, if you train while you’re sick, you may end up worse.

If you train when you’re not recovered, you can get a severe condition called post-viral fatigue syndrome. This can last for months and include weakness, fatigue, frequent infections and even depression.

Related Article: Can Hiit Be Done With Weights? (Yes, There Are 4 Rules)

How to Avoid Exercise-Related Sickness

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Doing too much of the same exercise, or too much exercise in general, can set you up for overtraining syndrome (OTS).

ACE Fitness describes this phenomenon as a “dose-response relationship”, meaning the more you workout the more benefits you will achieve, but there is a tipping point in which can do you more harm than good.

This point can be reached by: too much exercise without enough recovery or chronic under-fueling.

There are ACE Fitness’ telltale signs that you’re overtraining:

  • Decreased performance: you may notice a plateau in your fitness routine even after implementing the FITT principle or simply feel fatigued during your workouts.

  • Increased heart rate: you may find that it takes your heart rate longer to return to normal after a workout or that it stays elevated throughout the day.

  • Irritability or moodiness: since overtraining impacts your stress hormones the imbalance can cause mood swings, irritability, and inability to concentrate. 

  • Insomnia or poor quality sleep: excess stress hormones will also prevent your body from winding down and getting a good night’s sleep.

  • Appetite changes: working out definitely increases appetite, but a hormone imbalance can affect hunger and satiety signals in your body. You may find yourself without an appetite or eating a lot more than usual.

  • Chronic injuries and illness: some muscle soreness is part of working out, but pain that doesn’t subside in two weeks or so should be considered a notable injury.

Since overtraining taxes all the body systems, it makes it difficult to fight infections. Frequent illness such as upper-respiratory tract illness is a sign of overtraining. More severe medical complications may also include low bone mineral density and low testosterone.

When it comes to HIIT training, aim to keep it limited to 30 minutes or less per workout and aim for no more than two to three times per week.

Related Article: 30 Minute Full Body HIIT Workout: Total Body Resistance And Cardio

Sick To Your Stomach

Sometimes if you have a grueling workout, you may find yourself experiencing a different type of sickness. You may get nauseous or have to puke.

This is a relatively common phenomenon related to your digestive system and how exercise interferes with it’s normal processes.

When we work out, the blood moves to the muscles that are doing the work. As a result, there’s less blood being used for your organs, including your digestive system. So digestion is put to a halt.

In order to try and prevent these tummy troubles near a workout, plan enough time to break down food before a workout.

As a general rule of thumb, aim to eat one to three hours before a workout. If you’re eating closer to workout time, focus on lean protein and easily digestible carbs instead of fatty foods. Fatty foods take the longest for your body to digest.

Related Article: Who Can Benefit From Interval Training (Is It Good For Everyone?)

Benefits of Moderate Exercise

Regular exercise has been shown to have amazing benefits such as maintaining muscle mass, maintaining weight, and reducing the risk of chronic diseases such as heart disease and diabetes.

According to the health authority, WebMD, regular moderate exercise is the ticket to preventing colds and boosting immunity.

WebMD featured a study that showed how 20-30 minute walks every day, going to the gym every other day, or biking a few times a week, may cut down on the number of colds you get.

They also featured a study from the American Journal of Medicine that showed that women who walked 30 minutes every day for one year had half the number of colds when compared to those who didn’t exercise. Walking leads to a higher amount of white blood cells, which fight infections.

Moderate exercise that’s completed on an almost daily basis can have a cumulative effect that supports long term immunity. In one study, people who walked
40 minutes per day at 70-75% of their VO2 Max experienced half as many sick days than those who didn’t exercise.

Related Article: How Long Does It Take For HIIT Results? (10+ Things To Know)

Boost Your Immunity

In addition to moderating your exercise, fine-tuning your health routine with adequate sleep, rest days, stress reduction, and nutrition can support your body’s immune system and help it defend you against illness.


Sleep is essential for optimal health and wellbeing. During sleep, your body repairs and restores, including your muscles, immune system, and hormones.

Lack of sleep can cause inflammation and compromised immunity. According to MayoClinic, during sleep, your immune system releases cytokines that need to increase when you have an infection or inflammation. Sleep deprivation may decrease the production of these cytokines.

In a large study, it found that people who slept less than six hours per night or who had disrupted sleep were more likely to have colds.

Long term lack of sleep also increases your risk for obesity, diabetes, and cardiovascular disease.


Doing the same workout two or more days in a row doesn’t give your muscles time to recover and get stronger. Rest and recovery are just as important as daily movement.

According to the American Council on Exercise (ACE) you can practice active recovery between workouts including:

  • Taking a walk

  • Going for an easy bike

  • Doing a gentle yoga class

Read more about the importance of rest in between HIIT workouts: Should You Do HIIT Every Day? (5 things to Consider)


Research suggests that mindfulness meditation can help reduce specific markers of inflammation as improve cell-mediated immunity.

Since stress suppresses the immune system, managing stress through yoga, meditation, and deep breathing can help.

There isn’t a one-size-fits-all approach when it comes to stress relief. Here are some effective methods to start with. Aim to do at least one per day:

  • Meditation/mindfulness: non-judgmentally pay attention to the current moment. Focus on your surroundings, sights, sounds, smells, touch, and taste.

  • Focus on your breath: take air in through your nose and fill your lungs and belly with air. Count to three as you inhale, hold for one second, then slowly exhale.

  • Calm yoga: in the morning or evening, do a few easy yoga stretches such as corpse pose, child’s pose, or downward-facing dog. For images, check out Yoga Journal.


Food fuels our entire body system. If we support it with plenty of whole foods, fruits, and vegetables (aim for a wide variety of color) then you’ll get the immune-boosting nutrients, Vitamin C, zinc and protein.

Here’s where you can get them in food:

  • Vitamin C: citrus fruits (orange, grapefruit, lemon, lime), spinach and leafy greens, strawberries.

  • Zinc: whole grains, oysters, beans, nuts.

  • Good quality protein: fish, poultry (chicken, turkey), milk and dairy products, tofu, eggs, nuts and seeds.

Final Thoughts

Our bodies always tell us if we’re doing too much. We just have to listen. And when we don’t listen, it will slap us in the face with signs of low immunity until we do.

Regular physical activity can boost your body’s natural defense mechanisms but doing too much HIIT exercise (more than 2-3 times per week) can make you sick.

When it comes down to being healthy and feeling good in the long term, get in touch with your body, provide it with plenty of rest and recovery, support it with proper nutrition, and find trusted fitness plans.

About The Author

Lisa Booth

Lisa Booth

Lisa is a registered dietitian nutritionist (RDN) with over 15 years of experience in nutrition, fitness, and mental health coaching and education. She studied Foods and Nutrition at San Diego State University and earned a Master of Science in Holistic Nutrition at Hawthorn University.

Having certifications and experience in group exercise, intuitive eating, coaching and psychotherapy, and digestive wellness, she’s enthusiastic about the relationship between the body and mind.

She’s dedicated to helping people understand how to implement healthy habit change, while gaining a deeper understanding of what makes them feel their personal best.