Is HIIT (High-Intensity Interval Training) Bad for You?

The popularity of High-Intensity Interval Training (HIIT) is on the rise. It is a training regime that consists of short, acute sessions of high-intensity cardio and strength training. This regime can be followed on all common exercise modes, including cycling, walking, swimming, elliptical cross-training, and in many group exercise classes. 

HIIT is often marketed as an efficient workout program for weight loss. Many people learn about the benefits of HIIT and have a question: Will HIIT work for me, what is the downside? Though HIIT brings multiple benefits, it has some potential drawbacks, too. 

This blog will help you understand what happens when you overdo HIIT, when you should quit doing it, and some safety precautions you must follow. 

What is HIIT?

HIIT is an acronym for High-Intensity Interval Training. It is a type of interval training exercise consisting of alternate, short sessions of high-intensity movements (increasing the heart rate to at least 80% of the maximum rate) and low-intensity movements. 

The primary focus of HIIT during the exercise is the varying intensity level. It implies going from low to medium or medium to high and then dropping back before increasing it again. You can think of it as a series of short challenges. Initially, you push yourself harder for a few minutes and then slow down for an equal or slightly longer time period for recovery. 

Initially, HIIT was used only by athletes to improve their capacity for cycling, running, swimming, and other forms of cardio. Today, it is used by anyone, especially by people who are looking to lose weight or increase their cardiovascular fitness. 

You can do HIIT workouts at home, as they do not consume much space. Besides, they fit perfectly with aerobic exercises, such as running, dancing, climbing, cycling, brisk walking, and rowing on a machine. Body weight can serve as the primary source of resistance without requiring extra tools and equipment. 

How HIIT Works?

One of the reasons for HIIT’s popularity is the post-exercise calorie burn, which makes it more efficient than traditional steady-state exercise. 

The post-exercise period is called “EPOC,” which stands for Excess Post-exercise Oxygen Consumption. This is generally about a 2-hour period after an exercise where the body restores itself to pre-exercise levels and thus uses more energy. The vigorous contractile nature of HIIT workouts makes the EPOC modestly greater, adding about 5-15% more calories to the overall workout energy expenditure.

Besides its efficiency, studies have shown that HIIT results in increased metabolism, improved cardiovascular fitness and muscle tone, and weight loss. It can be done anywhere in a short period, without equipment, and in a group, and can be seriously challenging. It produces amazing results, as it targets a lot of muscles and burns calories in a large number. 

With so many benefits, more and more people are incorporating it into their exercise regimen. Although it is beneficial for everyone to indulge in HIIT, there are some cases where HIIT can do more harm than good.

When to Avoid HIIT?

I have seen people who exercise regularly feeling run down, losing muscle mass, gaining fat, and under constant exhaustion, which is completely contrary to their fitness goals. People often ask me, “I train hard to achieve my fitness goals. How and why am I not progressing?”.

First, every individual’s body is different and responds to exercise differently. People with rather sedentary lifestyles or periods of physical inactivity may have an increased risk of coronary disease due to high-intensity exercise. Family history, cigarette smoking, hypertension, diabetes (or pre-diabetes), abnormal cholesterol levels, and obesity will also increase this risk.

Is HIIT Bad for You? Effects of Overdoing HIIT

Many studies suggest that overdoing HIIT can backfire. While HIIT can improve your health and fitness, doing it excessively can overstress your body and reduce metabolism. Overdoing HIIT can be either in the form of duration or frequency of exercise.

One study published in 2021 suggests that prolonged high-intensity workouts may harm mitochondria, the powerhouse of energy found in cells. 

HIIT can wreck your body in following ways: 

1. Spike in Cortisol Levels

For those who suffer from high stress or adrenal fatigue, HIIT could cause serious harm to health. Intense exercise may place additional stress on adrenal functions. 

Cortisol is the body’s primary catabolic hormone, which is released by the adrenal glands under high mental and physical stress conditions. HIIT may stimulate significantly acute cortisol response. Chronically high levels of this hormone can increase the risk of a number of health issues, including weight gain, depression, digestive issues, chronic fatigue, sleep problems, and brain fog. Studies have found that excess cortisol can stimulate fat gain and cause poor-quality sleep. 


Both too much and too little cortisol can affect thyroid function. Elevated levels of cortisol can suppress the release of active thyroid hormone in various ways. For example, high cortisol may suppress the release of thyroid-stimulating hormones in the HPA axis. 

On the other hand, cortisol (required to convert T4 to T3, an active thyroid) is depleted in adrenal fatigue, which may lead to conditions such as hypothyroidism. This can cause depression, weight gain, and digestive dysfunction, along with a variety of other symptoms. In other words, a person might gain weight, which is counterintuitive and opposite to the desired objective of strength training.

Some symptoms of hypothyroidism are fatigue, lack of energy, sluggishness in the morning, poor concentration and memory, muscle pain, weakness or cramps, low sex drive, high cholesterol, and even low-grade depression.

Low-Carb Diet 

People often combine high-intensity exercise with low-carb diets; this is an additional factor in cortisol rise. Blood sugar level drops with low-carb meals, and the body needs cortisol to take glucose from muscles and the liver. This results in a rise in cortisol, which can, in turn, result in poor sleep and stimulate fat storage enzymes.

2. Difficulty in Replenishing Glycogen Stores 

During exercise, the body uses readily available energy sources. Initially, it uses free circulating sugar in the bloodstream. As the intensity of exercise increases, the body requires more energy, and this is where the role of glycogen, a form of carbohydrate, comes into play. 

Glycogen is a more powerful energy source than blood sugar. However, prolonged workouts without enough breaks between sessions can make it challenging to replenish glycogen stores. The depletion of glycogen stores can lead to fatigue, making you feel low and weak during workouts. 

The process of refilling glycogen starts after the workout session, and proper rest and enough nutrition are essential. Foods rich in carbohydrates post-exercise can help restore the energy required for the next workout session. 

3. Lack of Sleep 

HIIT, when done correctly, improves sleep. However, doing it close to bedtime can significantly disrupt sleep, making it tough to fall asleep. This does not apply to everyone, as every individual’s body responds differently to nighttime workouts.  

Intense exercise enforces stress on adrenal glands, releasing high levels of cortisol. Maintaining high cortisol levels all the time without natural ups and downs can cause disturbance in the sleep-wake cycle. 

4. Disrupted Metabolism

Excessive frequency and intensity of HIIT can have negative consequences on metabolism. 

The findings of one study conducted in 2021 state that excessive exercise training causes mitochondrial functional impairment and decreases glucose tolerance. 

In this study, health volunteers initially experienced improved health and performance during workout sessions. As they increased the frequency of HIIT to five times a week, their mitochondria were not able to produce enough energy to power cells. This also caused major disturbances in blood sugar levels and insulin secretion. 

5. Risk of Pain and Injury in Joints

During HIIT workouts, improper exercise techniques can lead to joint issues. An inconsistent form of exercise can make joints misaligned, which can put a lot of strain on the different parts of the body. This, in turn, can lead to injuries. This is especially true for plyometrics or high-impact movements.  

People with sensitive joints, especially those with arthritis or osteoporosis, should take proper care and limit high-impact movements during workouts. Box jumps, burpees, and jumping lunges can lead to a greater risk of joint pain and injuries. 

Should you Quit HIIT?

Done correctly, HIIT provides numerous health benefits for many people. It must be done in moderation while following proper exercise techniques to maximize its benefits. Compounding an already high-stress work or general life stress with the excess stress from exercise can actually make a person sick.

Many experts advise one rest or low-intensity day between HIIT workouts. Keep in mind your goals and accompany HIIT with other low-intensity exercise formats, such as yoga, aerobic workouts, pilates, etc. They are effective forms of exercise that provide powerful results. 

If you feel symptoms of overtraining, you can completely take off from HIIT workouts for a few months. As you recover, introduce short intervals of HIIT into your workouts. 

Symptoms of Overdoing HIIT

Overdoing HIIT can lead to many potential health conditions. Hence, it is essential to recognize body signals and signs of overtraining to avoid burnout before it leads to serious health issues. 

Here are the major symptoms of overdoing HIIT: 

An Example of a Beginner HIIT Workout 

Considering the effects of prolonged HIIT on health, it is important to be very careful while introducing it into the workout regime. 

Here is an example of a beginner HIIT workout: 

Safety Precautions for HIIT 

Here are some essential safety tips one must consider before incorporating HIIT into the workout plan:

  1. Do not skip warmup: A 5-minute warm-up before starting the actual exercise is essential to prepare the body for the main workout. It helps gradually raise the heart rate and increases blood flow to muscles. 
  2. Maintain correct posture: Doing an exercise with the correct posture not only helps maximize the benefits of the workout but also reduces the risk of injuries and joint pain. 
  3. Do not overdo: Overdoing HIIT can lead to many health issues, as discussed above. It is advised to limit your HIIT workouts to 2 to 3 times a week with a proper rest period. 
  4. Maintain a balanced diet: A nutrient-dense, protein-rich diet helps strengthen muscles post-workout. Also, it is not advised to start HIIT workouts on an empty stomach. 

How to Recover from HIIT?

Compounding an already high-stress work or general life stress with the excess stress from exercise can actually make a person sick. Adequate recovery from HIIT is vital in balancing hormones and avoiding adrenal burnout. 

Here is how you can recover from HIIT: 


A combination of high-intensity training, other stressors, and low-carb diets can raise cortisol levels and create weight loss resistance.

Do HIIT Workouts Correctly to Maximize Benefits 

The bottom line is that there is no one-size-fits-all approach to exercise, and the same applies to HIIT. If you make HIIT a part of your exercise regimen, ensure adequate rest and nutrition. Always use your best judgment and listen to your body. Avoid it and consider professional help if you have any of the symptoms mentioned above.

If you exercise regularly, I would like to hear about your experiences and know what kind of formats helped you achieve your goal. Do you feel that a particular kind of exercise affects your health negatively or does not have the desired impact? Feel free to comment below or reach out to us.

PS: Do you want to understand the underlying cause of your weight gain and follow a step-by-step program to lose weight and feel amazing? Contact us

If you are concerned about adrenal stress, you can start by checking your hormones with the Dutch test

Leave a Reply

Your email address will not be published. Required fields are marked *