Does Cardio Burn Fat: How Much and How Long?

Cardio exercise[1] or cardiovascular exercise aims to improve cardiovascular health and mitigate the risk of the development of cardiovascular diseases. Cardiovascular exercises mediate an improvement in myocardial calcium sensitivity and myocardial contractility following cardio workouts.

Aerobic exercise utilizes large muscle groups and is rhythmic. The major muscle groups stimulated in aerobic exercise are dependent on aerobic metabolism for the production of energy. Examples of aerobic exercise constitute dancing, long-distance running, jogging, cycling, hiking, walking, and swimming. The aerobic exercises are evaluated using the aerobic capacity of the body.

On the contrary, cardiovascular exercises, also called anaerobic exercises, do not depend on the utilization of inhaled oxygen as a source of energy for the contracting muscles. These intense exercises of short duration are dependent on energy sources present in the contracting muscles. The muscle cells produce energy from fermentation and glycolysis, which produces relatively less energy compared to aerobic exercises. Anaerobic exercises are related to the production and accumulation of lactic acid.

Anaerobic exercise is dependent on carbohydrate metabolism using the muscle glycogen stores. These exercises involve the fast twitch muscles. Examples of anaerobic exercises include power-lifting, sprinting, and high-intensity interval training.

How Much Cardio for Weight Loss? 

Cardio burns fat at a different rate depending on the volume and intensity of physical activity. Exercise training[2] at moderate training only allows significant weight loss and energy expenditure when there is a high volume of physical activity. According to the guidelines, the minimum of moderate-intensity continuous training of 225-240 minutes is associated with significant weight loss of ≥ 5% without combining cardio with restriction to a healthy diet. Overweight and obese adults who consume more calories are not guaranteed weight loss with moderate-intensity training. According to the current guidelines[3], individuals should engage in vigorous-intensity exercise for 75 minutes each week or moderate-intensity exercise for 150 minutes each week.

does cardio burn fat
Cardio burns fat at a different rate depending on the volume and intensity of physical activity.

How Does Cardio Exercise Burn Fat?

Core training comprising both anaerobic and aerobic exercises promotes a significant reduction in the levels of non-esterified fatty acids. Core training also promotes a reduction in the body mass index (BMI), helping individuals lose fat by burning calories. Compared to sprint interval training and high-intensity interval training, low-intensity exercise, moderate-intensity exercise, or moderate-intensity continuous training is less effective in burning fat mass and improving insulin sensitivity and cardiorespiratory fitness.

While carbohydrates constitute the main source of energy in the case of high-intensity exercise, fat burning is the predominant source of energy in the case of low-intensity exercise. Hence, vigorous-intensity exercise such as high-intensity interval training mediates fat loss despite low levels of oxidation of fat.

Body fat is present in fat cells or adipocytes, which are deposited in different areas of the body. When individuals lose body fat and reduce body weight, there is an improvement in the dysfunction of adipose tissue. Besides improvement in metabolic health, physical activity helps lower insulin resistance and increase insulin sensitivity.

Calorie expenditure[4] in humans is a combination of energy expenditure during rest and physical activity. During high-intensity exercise, there is an increase in oxygen uptake, which results in the development of an oxygen deficit, which is larger enough to surpass the anaerobic threshold. The oxygen deficit is fulfilled by the consumption of extra oxygen for paying the oxygen debt.

Excess post-exercise oxygen consumption increases following high-intensity interval training have implications on both the adipose and the muscle tissue. High-intensity exercise increases insulin sensitivity and lipolysis. In the muscle tissue, oxygen consumption restores muscle glycogen and increases protein turnover and oxidative phosphorylation.

The loss of fat mass in high-intensity exercises is far greater than the expected amount. This is due to a greater workload in the case of moderate-intensity continuous training compared to high-intensity exercise.

Exercise training changes body composition without influencing the total body weight. The body composition remains unchanged as the muscle mass increases and fat mass decreases. The combination of resistance training and high-intensity interval training is associated with a reduction in the deposits of visceral and subcutaneous fat with a simultaneous increase in muscle mass, without resulting in weight gain or weight loss.

does cardio burn fat
Cardio workout on a treadmill.

Best Cardio Exercises to Lose Weight

The best cardio exercises that help individuals lose weight include high-intensity interval training, low-intensity, and moderate-intensity training, moderate-intensity continuous endurance training, and sprint interval training. These exercises help lose weight and burn more calories by mediating fat loss.

How Long Should You Do Cardio to Lose Weight?

The duration of cardio and strength training for promoting weight loss and burning fat for attaining a healthy weight is described in the preceding sections. Studies have demonstrated that high-intensity interval training is more effective than moderate-intensity training in promoting weight loss within a short duration of time. Simultaneous to fat burning, the addition of strength training exercises also mediates an increase in muscle mass.

Myths About Cardio for Weight Loss

One of the myths about cardio exercises for weight loss is the notion that the greater the cardio, the more calories are burned and more fat loss occurs. However, it should be noted that high-interval intensity training exercises should be performed within the recommended duration of 75 minutes each week. Excessive exercise training[5] is known to cause reduced glucose tolerance and impaired mitochondrial function in healthy individuals. This is also associated with a disturbance in the secretion of insulin.

Extreme amounts of exercise training may cause myocardial fibrosis, arrhythmia, and coronary artery calcification. While an appropriate exercise stimulus causes improvement in physical and physiological performance, too much exercise training results in a reduction and staleness of physical performance.

Another common myth that shall be addressed in the case of cardio exercises is that such exercises can help fat loss even if individuals do not consume a healthy diet. While cardio burns calories, actions such as healthy eating and lifting weights help burn more calories, which aids in losing weight. The incorporation of strength training in the exercise is also beneficial as strength training aids in increasing the metabolic rate, promoting fat metabolism in the body.

Benefits of Cardio for Weight Loss

Anaerobic exercises are implicated in an increase in the levels of catecholamines[6] including noradrenaline and adrenaline. The levels of noradrenaline increase significantly during aerobic exercises. The levels of cortisol and insulin also tend to rise during anaerobic exercises, however, the rise in the levels of insulin is not observed in the case of aerobic exercises. Both exercises involve a rise in the levels of estradiol and testosterone hormone levels in the blood.

There are relatively higher levels of sympatho-adrenal activity in the case of anaerobic exercise compared to aerobic exercise. Further, intense prolonged exercise particularly influences the levels of cortisol and growth hormone in the body. While moderate and high-intensity exercises stimulate an increase in the circulating levels of cortisol, low-intensity exercise causes a reduction in the levels of circulating cortisol[7] in the body. Individuals engaging in aerobic exercises tend to experience larger changes in their stress and well-being compared to individuals who engage in anaerobic exercises. This suggests that aerobic exercises[8] positively influence the well-being of individuals.

does cardio burn fat
Using rowing machine for weight loss.

Conclusion

In summary, cardio workouts cause different muscle groups to engage and use oxygen or the pre-existing fuel stored in the body to produce energy for muscle contraction. Cardio exercises are not only useful for promoting cardiovascular health and decreasing the risk of cardiovascular disorders, but these exercises are also useful for promoting fat loss and increase in muscle mass if combined with strength training exercises.

While high-intensity interval training is useful for promoting faster fat loss, the duration of exercise should be within the recommended limit of 75 minutes each week, so as to limit impairment in glucose tolerance and mitochondrial function.

Frequently Asked Questions

What are some examples of cardio exercises?

Examples of cardio exercises include high-intensity interval training, low-intensity, and moderate-intensity training, moderate-intensity continuous endurance training, and sprint interval training.

What is the difference between high-intensity and moderate-intensity exercise?

High-intensity interval training is associated with a short duration and greater fat compared to moderate-intensity training which has a higher workload. Furthermore, individuals who supplement moderate-intensity exercise with greater calorie consumption do not tend to reap the weight loss benefits of these cardio workouts.

What happens when an individual performs too much high-intensity exercise?

The drawbacks of excessive high-intensity training include reduced glucose tolerance and impaired mitochondrial function in healthy individuals. Extreme amounts of high-intensity training may cause myocardial fibrosis, arrhythmia, and coronary artery calcification.

How does a high-intensity workout stimulate increased muscle mass and decreased fat mass?

High-intensity workouts mediate increased muscle mass and decreased fat mass by excess post-exercise oxygen consumption and by increasing the metabolic rate of the body, which results in a greater expenditure of energy.

What is the recommended duration of moderate and high-intensity training?

According to the current guidelines, individuals should engage in vigorous-intensity exercise for 75 minutes each week or moderate-intensity exercise for 150 minutes each week.

How do anaerobic and aerobic exercises influence the hormone levels in the body?

The levels of noradrenaline increase during aerobic exercises. The levels of cortisol and insulin tend to rise during anaerobic exercises, however, the rise in the levels of insulin is not observed in the case of aerobic exercises.

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