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How does cardio burn fat?

The 6 most common myths about cardiovascular exercise and losing body fat debunked by science.

Cardio exercise is one of the most efficient ways to burn fat. Regular running, cycling, and high intensity interval training (HIIT) sessions can provide visible results. Despite there being research on how exercise impacts fat loss, the process is still not fully understood. While we know that cardio exercise burns calories and fat, several other factors like genetics, nutrition, and hormone levels can impact results. These are the 6 most common myths about cardiovascular exercise and body fat loss—debunked by science to help you maximize your results.


Myth 1. Everyone must burn 3500 calories to lose 1 pound of weight.


Truth: There’s no “one size fits all” number. The body fat burning process depends on many factors, including weight, diet, and exercise habits.


The primary idea behind any fat-loss program is to burn more calories than you consume. Our body does this in different ways. First, there’s a basal metabolic rate—the amount of energy our body needs to maintain all necessary functions (breathing, heart rate, digestion, etc.). Basal metabolic rate is the number of calories we burn daily without any additional activities, and it varies significantly depending on age, sex, muscle mass, and genetics.


Then, there’s activity rate. You can opt for different kinds of activity be it cardio, strength training, or resistance training, and each will contribute to fat loss to a different extent.


Cardiovascular (aka aerobic) exercise increases heart and breathing rates, thus requiring more oxygen. These exercises (such as running or cycling), typically involve repetitive movements using large muscle groups. Conversely, anaerobic exercises (such as strength training or weight training) involve short, fast, high-intensity activities that don’t require much oxygen but do improve the body’s endurance.


Some sources say that you need to burn approximately 3500 calories to lose 1 pound. However, a mathematical model created by the National Institutes of Health challenges this belief. It shows that the correlation between calories and pounds of body weight burned varies depending on weight, diet, and exercise habits.


The takeaway? You must form your own personal training program depending on your condition and the amount of fat mass you want to burn. The U.S. Department of Health and Human Services provides a general recommendation that people should get at least 150–300 minutes of moderate-intensity exercise or 75–150 minutes of vigorous-intensity exercise each week in order to see changes.


CAROL Bike is designed to get you fittest, fastest. Science-backed Reduced Exertion HIIT (REHIT) workouts deliver double the health and fitness benefit compared with regular exercise, in 10% of the time. Find the best CAROL workouts for your health and fitness goals.

The body fat burning process depends on many factors, including weight, diet, and exercise habits.

Myth 2. When fat is burned, it is converted to energy or heat.

Truth: Fat cells are broken down into carbon dioxide and water.

The extra carbohydrates and proteins we eat are converted to triglycerides and stored as fat. During exercise, our body first uses all available energy stored in blood glucose, and then it looks to burn calories from fat mass. This starts a chemical reaction, breaking down triglycerides stored in fat mass and using the released energy for activity.


Many people believe that fat is converted to energy or heat, but research published in the British Medical Journal shows that fat mass is converted into carbon dioxide and water (as most other nutritional elements are). The water is excreted in body fluids, and carbon dioxide is primarily excreted by the lungs. This shows how cardiovascular activity helps burn fat by increasing breathing rate and oxygen use.


Myth 3. Aerobic exercise should last at least 30 minutes to produce a fat-burning effect.

Truth: Special protocols like HIIT and REHIT reduce the training time to 5–10 minutes while yielding more efficient results.


During light aerobic exercise or short workouts, our body uses glycogen (the stored form of glucose). It is only after about 20 minutes that our muscles switch to the fat-loss mode. It is true that 30–60 minutes of lower- or moderate-intensity exercise are necessary to achieve efficient fat loss.


High intensity interval training (HIIT), however, is a special training protocol that starts fat metabolism faster, thus reducing the training time to 20–30 minutes. HIIT repeatedly alternates short periods of intense exercise with brief recovery periods until the point of exhaustion.


Scientists further optimized this protocol to REHIT, the shortest, most effective way to exercise. REHIT can be done in just 5 minutes, with 2×20-second sprints interspersed with a short recovery period as well as a warm-up and cool down.


A study published in the International Journal of Environmental Research and Public Health proved that 8 weeks of a REHIT program significantly improved cardiometabolic health when compared with traditional moderate-intensity continuous training (MICT).


The primary challenge is that REHIT sessions are not easy to replicate outside of the lab. To make the most out of your aerobic training, CAROL Bike is the best way to introduce REHIT into your practice because it provides the necessary supra-maximal resistance tailored to each individual’s physiology. As a result, CAROL Bike gives you the same health and fitness benefits as a 45-minute run in just 5 minutes. Read more about the science behind CAROL Bike here.

Get the benefits of a 45 minute run in just 5—with CAROL Bike.

8 weeks of a REHIT program significantly improved cardiometabolic health when compared with regular exercise.

Myth 4. You only lose fat while training.

Truth: Post-exercise fat burn makes your training more efficient.


Cardiovascular exercise ignites a number of metabolic and hormonal function effects that last long after training, which helps you burn fat even during rest.


Once a workout is over, the body continues to increase oxygen use to restore muscle glycogen and rebuild muscle proteins damaged by exercise. This process is known as excess post-exercise oxygen consumption (EPOC)—the amount of oxygen required to return the body to its normal resting metabolic function.


High intensity interval training (HIIT) and the modified REHIT are the most efficient methods for stimulating EPOC. Research shows that these methods produce greater post-exercise resting energy expenditure and respiratory exchange ratio in women than does any other type of training.


Another useful effect of aerobic training is decreased appetite. A study of 19 female exercisers—9 runners and 10 walkers—who completed a 60-minute moderate-intensity run or walk, showed exercise-induced alterations in appetite that are likely driven by complex changes in appetite-regulating hormones.


HIIT also helps lower insulin resistance. Fat prevents the liver from responding well to insulin; therefore, the body produces more insulin, which goes on to store more body fat, creating a vicious circle. Suppressing insulin secretion and improving insulin resistance are both associated with body weight and fat loss.


Myth 5. Cardio training in a fasted condition helps you burn more fat.


Truth: Fasted cardio training doesn’t lead to increased fat burn.


Exercise and nutrition are generally used in combination to lose body fat and reduce weight. Some people believe that training in a fasted condition can enhance weight loss by stimulating lipolytic activity. Such training sessions usually happen early in the morning before breakfast, but they can also be scheduled in the afternoon if intermittent fasting is practiced.


However, research proves that training on an empty stomach doesn’t impact results. While being generally safe for your health, fasted cardio training doesn’t lead to increased fat burn.


Some also argue that being faced with a calorie deficit while performing its basic functions can cause the body to enter starvation mode, slowing down metabolic rate. This results in needing even more hours of training to lose weight.


Myth 6. The more cardio training you do, the better results you get.


Truth: Overtraining can prevent you from achieving maximum results.


Overtraining can be bad for your health and can slow your progress or even lead to weight gain. This is especially true for HIIT protocols, which require a careful approach.


In addition to increasing your risk of injury, overtraining can increase inflammation and cortisol, and it can slow your metabolism down. All of these factors can impede results.


Cortisol is known as the stress hormone. High levels of cortisol can cause stores of fat mass, especially in the abdomen. When left unchecked, this can increase weight gain even further. Research shows that moderate- to high-intensity exercise increases cortisol circulation level whereas low-intensity exercise actually reduces cortisol circulation level.


If you want to lose fat efficiently and get in better shape, it’s best to rely on science. A comprehensive fat-loss program will combine aspects like regular training, varied diet, a good amount of sleep, and a healthy lifestyle. Remember, you don’t need to overtrain and spend hours each week to lose weight. Even a 5-minute cardio REHIT workout incorporated into your exercise routine will make a significant difference.

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