Why Am I Gaining Weight Doing HIIT: Here’s How Too Much Exercise Throws Your System Off-Kilter

HIIT exercises have gained popularity in recent years and they are famed for their incredible role in helping many lose weight. However, as much as many are shedding off those unwanted pounds, you may realize that in your case, the scale keeps going up. If this is so and you’re wondering ‘Why am I gaining weight doing HIIT?’ read on to find out why this is happening to you.

Does Working Out Make You Gain Weight?

In a way, yes, but before you start freaking out, allow us to explain how and why this may be happening. Losing weight is the reason why a chunk of the population starts working out and seeing the scale go up instead of down can be rather frustrating and demoralizing. 

However, it’s important to realize that what you’re going through isn’t a rare/isolated incident and gaining weight after working out is actually quite common. 

Why You May Be Gaining Weight After Working Out

Here are some reasons behind it (11):

• More Muscle Equals More Weight

While people often associate HIIT workouts with fat and weight loss, these exercises are in fact a great way to build muscle. In one study published in the Frontiers in Physiology journal, researchers found that doing HIIT workouts on a stationary bicycle can help promote increases in lean mass, maximal strength, and lower-limb muscle power in both healthy older and young individuals (1).

Now, unlike fat, muscle isn’t easily seen, particularly at the start of your weight loss journey. While muscle and fat weigh the same, the former is more dense, which means that it occupies a much smaller space in the body. This means that you may look smaller but the scale shows a much higher number than you’d like to see. 

Due to this, you need to remember that bathroom scales do not differentiate fat from muscle, bones, blood, and other fat-free mass in the body. So, if you have been doing everything right but the number is a little high, try investing in a body fat scale or finding a location to get a body composition analysis instead as it just might help put your mind at ease. There are many professional devices that can be used to give you an accurate reading of your body fat percentage, skeletal muscle mass, water weight, and any muscular imbalances. These are referred to as body composition analysis tools and they can be very accurate. 

• Water Weight

As seen above, fat is not the only thing that can make the scale go up. In addition to extra muscle, having extra water trapped in the body can also make the number on the scale increase. 

Also known as edema, this condition is caused by multiple factors, including your hormones, a high sodium and carbohydrate intake, dehydration, illnesses such as kidney or heart disease, certain medications, and instances of physical inactivity (2). 

Thankfully, for the most part, having excess water in the body isn’t a complicated or life threatening issue and it can be fixed with just a few changes to your diet and lifestyle. In addition, your muscles store water and your body will sweat it out through exercise and throughout the day. 

Reducing your sodium or carbohydrate intake, exercising, and even drinking more water can help flush up the excess water. For those with underlying illnesses or who are taking medication that can make the body hold on to water, speaking to your doctor can help you manage this.

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• Post-Workout Inflammation

As mentioned above, doing HIIT workouts, or any type of exercise in general, builds muscle. However, in order for these muscles to be built, they need to be broken down first. The stress put on the muscles during a workout session damages your muscle fibers and after rest (and a healthy high protein diet) you’re able to repair and rebuild the muscles, making them bigger and stronger (3).

However, when you damage these muscles via exercise, they are inflamed, which causes your white blood cells to come to these fibers to try and fix them. Sometimes, these white blood cells can end up building up within the damaged cells (4). This build-up of cells and the aforementioned inflammation can register as weight gain on the scale. Thankfully, this is only temporary and usually disappears on its own.

• Post-Workout Supplements

Post-workout supplements are quite popular in the fitness community as they can help reduce the effects of exercise-induced muscle damage (i.e. muscle weakness and pain), which can reduce an individual’s ability to exercise.

One study published in Nutrients stated that some of the ingredients used in these supplements help with post-workout recovery (5). An important point to note is that a lot of these supplements, especially the beverages, are higher in carbs. 

While carbs are good for muscle growth (they are turned into glucose and then stored in the muscle as glycogen for later use), they can lead to water retention.

One study published in the European Journal of Applied Physiology stated that for each gram of glycogen stored, the body retains three grams of water (6). As previously mentioned, water retention can show up as weight gain on the bathroom scale.

Read more: 10 Upper-Body Mobility Exercises You Can Do at Home

• Your Diet

It’s not enough to just do a HIIT workout every day and assume that the pounds will start falling off. Your diet is just as important, if not more so, to your weight and fat loss as working out (7). Drop all the unhealthy foods and sugars, then replace them with leafy greens, oily fish, fruits, legumes and lentils, and whole grains. 

Remember to also track your calorie intake to ensure that you’re not under- or overeating for your goals and level of physical activity. Without a proper diet, the question ‘why am I gaining weight doing HIIT?’ will continue to haunt you.

So can exercise cause weight gain?

Yes, it can, but the weight is likely not due to an increase in fat but rather through an increase in muscle or water retention. Water retention is super easy to get rid of and more muscle gain is better for you as it improves both your physical and mental health (8).

Check out our article on beach body HIIT workouts to learn more about the best workouts to help you build the beach body of your dreams.

What Are Some Benefits of HIIT Training?

Here are some ways in which engaging in HIIT exercises could improve your health and quality of life

• Weight And Fat Loss

HIIT training is fantastic for anyone who wants to reduce weight and the amount of fat in their body. In 2012, a controlled study found that people who did 20 minutes of HIIT exercises for 12 weeks reduced their weight by 1.5 kg. They also lost 2 kg of total fat mass during this time (9). Another thing is that HIIT workouts also keep your metabolic rate running fast long after the workout session is done. This also helps with calorie burning, which can help with your fat and weight loss goals (10).

• Improves Cardiovascular and Respiratory Health

Studies over the years have shown that HIIT workouts can help protect the heart health of healthy patients. In patients dealing with cardiovascular problems (e.g. chronic congestive heart failure), studies have also shown that participating in interval training helps improve their cardiac function and physical performance (11).

HIIT workouts also help improve your cardiorespiratory fitness, i.e. the ability of the circulatory and respiratory systems to supply oxygen to skeletal muscles during sustained physical activity. This effect is good for healthy individuals as it can help them perform physical activity better without getting winded quicker, and it’s also essential for patients who suffer from pulmonary illnesses (12, 13).

• It’s Not Time-Consuming

Ordinarily, a normal workout session can take anywhere from 45 minutes to an hour from start to finish. On the other hand, HIIT takes 20 to 30 minutes, including warm-ups and cooling down. This makes it the perfect routine for anyone with a busy schedule or someone who just doesn’t want to spend an eternity at the gym.

• It Increases Your Vo2 Max

Also known as maximal oxygen consumption, this refers to the maximum amount of oxygen an individual can utilize during intense or maximal exercise. Studies have shown that doing HIIT exercises can improve your VO2 max, which boosts your athletic performance (14, 15, 16).

• It’s Good for Your Mental Health

Generally, exercising is good for mental health issues ranging from anxiety and stress to more complex and chronic illnesses such as depression and schizophrenia. 

Multiple studies have shown that this kind of exercise can be used for the treatment and management of common mental health issues such as depression and anxiety to severe mental illnesses such as chronic schizophrenia (17, 18, 19, 20).

• Boosts Your Metabolism for Hours After the Workout

In 2012, a published study showed that a 2-minute sprint can boost your metabolism for up to 24 hours. This is the same boost that you would likely get after doing endurance training for about 30 minutes (21). In 2014, a comparative study also showed that despite the short amount of time spent doing HIIT, the amount of oxygen energy consumed in the following 24 hours was similar to that consumed after performing traditional endurance exercises (22).

• Muscle Growth

HIIT exercises are said to place the same amount of stress on the muscles as resistance exercises (23), which explains why studies continue to show that this workout is great for increasing muscle size and strength (1, 24, 25).

Are HIIT Workouts Good for Weight Loss?

Yes, they are. A great HIIT workout routine will burn calories during the workout and keep your metabolism high enough for you to continue expending energy hours after the routine is done. Below is a sample HIIT routine you could try for weight loss.

Sample of a HIIT Cardio Workout at Home: No Equipment

While no equipment is necessary for this HIIT cardio workout for beginners, you’ll need a timer, a clear area around you, and a comfortable surface, e.g. a gym or your home with an exercise/yoga mat. With this form of exercise, you’re meant to move fast and have minimal rest periods. If you’re new to exercise, please be cautious when performing this circuit as it’s going to be difficult to do if you’re not in the best cardiovascular shape. As always, remember to consult a doctor before you attempt any form of exercise, particularly if you have a chronic illness.

Step 1 – Warm-up

Each of the following exercises should be done for 30 seconds.

• Swinging Arms Jumping Jacks

Instead of bringing your arms up and down, swing your arms outwards and sideways as you jump and spread your legs, then bring them together and forward as you bring your legs together.

• Front Kicks with Reaching Arms

Pull your arms up and down as you kick forward with each leg.

• Standing Alternating Toe Touches

Standing with your feet hip-distance apart, swing your right leg up and touch your left hand to your right toes. Return to the starting position and repeat with your left leg, touching your right hand to your left toes. Remember to keep your chest up.

• Leg Swings

Lift one straight leg and swing it straight forward and then backward in a controlled pendulum-like fashion. You can hold onto a wall or the back of a chair for balance. Do 30 seconds on the right leg before switching and repeating the movement on the left side.

• Butt Kicks

Stand with your feet hip-width apart, core engaged, and your hands placed on your hips. Jog in place, kicking your heels high to try to tap your butt.

Step 2 – Working Sets

Each of these exercises should be done for 45 seconds.

• Tap and Clap Jump Squats

1. Stand with your feet wider than hip-width apart and your hands by your side. Squat down, tapping the floor.
2. Rise from the squat, jumping with your feet together while clapping your hands behind your back (or just in front of you).
3. Repeat, immediately jumping back to the squat and tapping the floor.

Remember to keep your core engaged and breathe through the workout. A good rule of thumb is to breathe in when you are lowering yourself in a squat and then breathe out as you push yourself back up from the squat.

• Twisting Hops/ Jumping Oblique Twists

1. Stand with your feet together and bend your elbows, bringing your arms to your waist.
2. Jump up 3 to 4 inches off the ground and rotate your lower body to the right.
3. As soon as you land, jump up again and rotate your lower to the left this time.

• Mountain Climbers

1. Begin in a traditional plank position with your shoulders directly over your hands and wrists.
2. Make sure to keep your back flat and your butt down, maintaining a neutral spine. Don’t curve your back or sag your hips.
3. Engage your core and lift your right knee, bringing it toward your elbow (or as far as you can). Return the right knee to the starting position as you simultaneously drive your left knee up toward your left elbow.
4. Return to the starting position and continue switching legs as you pick up the pace. It should feel as if you’re running in place in a plank position.

Take a 30-second active break (i.e. move around a little) before repeating all the workouts on step 2 once more.

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Step 3 – Working Sets

As with step 2, all these workouts should be done on a 45-second timer. Remember to pace yourself and take it slower if you need to. It’s better to safely get through the exercises than to rush with bad form. 

1. Burpees

• Start in a standing position with your feet shoulder-width apart.
• Squat down with your back straight and your hands on the floor between your feet.
• With your weight on your hands, kick your feet back, so you’re on your hands and toes and in a push-up position.
• Do one push-up before jumping your feet back to the starting position.
• Push strongly from this position and jump, reaching your arms over your head.

Beginners should omit the push-up (or do a knee push-up) if they find this variation too difficult.

2. Curtsy Lunges

1. Start by standing with your feet hip-width apart and place your hands on your hips.
2. Take a big step back with your right leg, crossing it behind your left. Bend your knees and lower your hips until your left thigh is nearly parallel to the floor.
3. Keep your torso upright and your hips and shoulders as square as possible to the wall in front of you.
4. Return to the start position and repeat the movement on the other side.

3. Arm Reaching Crunches

Instead of tucking your arms behind your head or crossing them over your chest as you normally would during crunches, push them up and reach to the ceiling as you come up and fold them as you lower yourself to the ground.

Take a 30-second active rest and repeat all exercises listed in step 3. 

Step 4

• Backward Lunge with High Knees

Do 4 reverse/backward lunges (2 on each leg). Once you come back up, jump straight into 8 high knees (4 on each leg).

• Bicycle Crunches

This is a great variation of the arm reaching crunches above. In this workout, place your arms behind your neck and pedal your legs as if you are riding a bicycle. Bring your right elbow toward your left knee and extend your right leg and vice versa.

• Jump Squats

1. Start by standing tall with your feet shoulder-width apart.
2. Keeping your chest up, core engaged, and back flat, push your hips back and lower your body until your thighs are parallel to the floor.
3. Push yourself back up explosively, jumping straight up.
4. Land softly, lowering yourself immediately into your next rep.

• Frog Jumps

This is a simple exercise that’s reminiscent of something many of us did when we were younger. Pretend you’re a frog and try to jump around. There are no specific instructions for this one. Just repeat what you did in your childhood for 45 seconds. This will help your body stay in a deep squat while also continuously moving around to keep your heart rate elevated.

Take a 30-second break before repeating all the workouts outlined in this step.

Step 5 – Active Cool-Down

• 1 minute of alternating front kicks and squats. Kick once on each side, then squat. 
• 1 minute of forward lunges.
• For both of these cool-down exercises, focus on doing them slowly and trying to control every part of the movement. The goal is to get your body to relax after the vigorous workout you just completed.

For more exercise examples and plans, check out this article on HIIT for beginners.

HIIT Calories Burned vs. Typical Workouts: How Many Calories Are Burned in 30 Minutes of HIIT? 

Many factors influence the amount of calories a person will burn through a given exercise. However, the main difference between calories burned during HIIT sessions and those burned in typical workouts is that the former typically burns a larger number of calories in a shorter time period than the latter. Regarding the number of calories you’re likely to burn in either session, calorie burning is individual and based on several factors, so it would be difficult to give an accurate number. 

If you’re looking for exercise plans that burn a lot of calories, check out the article on workouts that burn 1,000 calories.

Read more: Why Isn’t Intermittent Fasting Working for Me?

Why Am I Gaining Weight While Dieting and Exercising?

Here are some potential reasons why you could be gaining weight despite dieting and exercising:

• A High Sodium Intake

Even while making healthier choices, it’s good to realize that these foods can have more sodium than you realize. Sodium can increase the amount of water that the body retains. In addition, research has shown that diets higher in salt can lead to weight gain and obesity in both children and adults (26, 27).

• You’re Not Eating Enough

Cutting your daily caloric intake is the first step in losing weight. Research has suggested that eating in a calorie deficit of  500 to 1,000 calories a day can be effective for fat and weight loss. Reducing more than this causes your body to believe that you’re starving, which makes it hold on to fat to protect you from this assumed starvation. 

• You’re Over-Exercising

If you’re spending up to an hour or more doing HIIT exercise, you might have the answer to ‘why am I gaining weight doing HIIT?’ Yes, this kind of workout does mean high-intensity, but that doesn’t mean you should over-exert yourself for the sake of an increased calorie burn.  Working out too much leads to overtraining. Increased fat and weight gain are among some of the other side effects of too much HIIT training with little to no rest (28).

Frequently Asked Questions

• What are the disadvantages of HIIT training?

HIIT workouts are generally safe for people to do. However, overdoing them can lead to the above-mentioned overtraining syndrome, which in addition to weight gain, can also lead to excess fatigue, mood swings, muscle loss, depression, hypertension, anxiety, and concentration issues (29).

In addition, this style of training can get your heart rate up very high for an extended period of time. This may be dangerous for individuals with heart conditions, so please contact your healthcare provider before getting started on this form of exercise.

• Why does HIIT make me puffy?

This could likely be due to water retention or perhaps due to some post workout inflammation. As we’ve discussed, sodium can play a role in water retention and too much of it can give you a puffy appearance. 

• Does HIIT make you bulk?

As explained above, HIIT exercises can help with muscle growth, so they may help you bulk, particularly if you do weighted HIIT workouts combined with an appropriate calorie intake that puts you in a calorie surplus rather than a deficit.

• Can intense exercise cause weight gain?

Yes, it can. However, the weight gain is rarely due to increased fat but due to muscle gain, water retention, or overtraining symptoms. 

The Bottom Line

Yes, you can still gain weight while doing high-intensity interval training, but as explained above, this kind of weight gain is likely not something to worry about. Most of this gain is temporary as it’s due to having excess water in the body. It can also be due to muscle gain, which is definitely not a bad thing.

If you’re unsure of what is causing weight gain after a workout, it’s best to consult a doctor to try and find the root cause of the issue. Also, make sure you speak to a doctor before you attempt any of the above exercises as they’ll have your heart rate up for an extended period of time.