- The initial phase of learning and adapting to any cardio activity requires more energy and burns more calories but ultimately when you master it, doing the same cardio activity will not burnt as much calories.
- High-Intensity Interval Training (HIIT) is more effective in burning a noticeable amount of calories in an individual’s body during and post-workout.
- The “interference effect” of cardio with resistance training depends on the frequency of cardio sessions as well as the gap between cardio and resistance training.
- Studies have shown, a combination of cardio and resistance training is appropriate.
Whenever fitness is discussed, we end up hearing how cardio can be the mystical tool for your weight loss journey.
As a beginner, you wouldn’t be expected to lift a 20 kg dumbbell or perform a deadlift with impeccable form, but simply doing cardio is like a one-size fits all solution. It’s a no-brainer and the easiest form of exercise to kickstart your weight loss journey. However, it is crucial to understand how to effectively utilise cardio as a tool to maximise your results.
You will find several definitions of cardio on the net, while what it essentially means is, a form of exercise to get your heart rate up. One interesting definition on a blog said, “Cardio exercise simply means that you’re doing a rhythmic activity that raises your heart rate into your target heart rate zone, the zone where you’ll burn the most fat and calories” . Here, while the first part of the definition is neutral, the second part makes a huge claim. And that is exactly our focus. This is a common misconception that doing cardio everyday is essential to lose weight or only doing cardio will be sufficient to help in your fat loss journey.
Here, the term exercise economy, coined by Barnes and Kilding (Biolayne), is of help. It basically means the amount of energy you consume while working out. The concept is based on the belief that the initial phase of learning a certain workout requires more energy and burns more calories but ultimately when you master it, doing the same workout will not consume as much energy and the calories burnt will also reduce . This means that after a point, you would stop seeing any results. That’s exactly what happens with cardio.
Moreover, there is an interesting fact about cardio and calories. Whatever additional calories you lose through your cardio, over and above your basal metabolic rate (BMR) (say 300 calories in one treadmill session), is something that you can easily substitute with an equivalent reduction in your daily macronutrient intake, say a few grams of carbohydrates per day .
Also, if you think that you lose fat only during a workout, then you are mistaken. You might have heard your trainers often referring to something known as an after burn or EPOC (Excess Post-exercise Oxygen Consumption). In this, the body starts to consume more amount of oxygen post a workout session, which expends several calories during the process. However, you do not burn the same amount of calories with every cardio activity. An exercise physiologist was quoted in an article by NY Times wherein he said that the effects of low-intensity cardio like walking or jogging is not as much, in terms of calories. He suggested High-Intensity Interval Training (HIIT) which generally consists of 30-45 minutes of high-intensity workout, as being more effective in burning a noticeable amount of calories in an individual’s body during and post-workout .
In the hurry to reach a goal faster, individuals tend to find a shortcut to everything. Without proper research or any professional guidance, they begin doing such intense HIIT workouts and are motivated by the results they see in their body. Despite all the positive effects of HIIT workout and its ability to help you lose weight quickly, what they miss out on is the lack of muscle or strength. This is not to say that you wouldn’t gain any muscle or strength but the frequent and extreme energy-consuming bouts slow down the whole process. Dr. Eric Helms calls it the “interference effect” since doing lifts immediately after a high-intensity cardio is going to interfere with your ability to do so.  In an interview, he advises a combination of cardio and resistance training. Along with that, he also says that it depends on the frequency of cardio sessions as well as the gap between cardio and resistance training. A few times, like 2-3 sessions a week and on separate days from strength training and weight lifting is going to minimize the interference effect.
This resonates with a study conducted by Duke University wherein 3 groups of students were taken and one was assigned resistance training, the other aerobic training and lastly, a combination of the two for the third group. At the end of eight months, students of Group 3 had lost the maximum weight and gained muscle at the same time. Group two (aerobic training), was found to have lost the most muscle. 
All of this discussion brings us back to the point where we started i.e. the exercise economy. Doing only cardio or only one type of activity makes your body accustomed to that routine and it increases energy efficiency. Overtime, you’ll burn less calories and start over eating due to this calorie deficit. And finally, this won’t help you reach your goal. Instead, it’ll take you far, far away from it. Nonetheless, it is vital to be well-informed about your goals and plan your workout schedule accordingly. 
So, let’s assume that your aim is to lose fat. The first and foremost question to ask is that will devoting several hours to cardio in a week help me reach my goal.
- Matthews, M. (2017). “Dr. Eric Helms Answers: What’s the Best Way to Combine Cardio and Weightlifting?”. Legion Athletics. Retrieved August 28. https://legionathletics.com/eric-helms-interview-cardio-weightlifting/
- Matthews, M. (2017). “Is weightlifting or cardio best for weightloss?”. Retrieved August 28. Legion Athletics. https://legionathletics.com/weightlifting-or-cardio-for-weight-loss/
- Pardue, A. A. (2017). Kill the cardio? Biolayne. , 2020. Retrieved August 28. https://www.biolayne.com/articles/training/kill-the-cardio/
- Schoenfeld, B. (2011). “Maximizing Fat Loss from Cardio”.Look Great Naked. , 2020. Retrieved August 28. http://www.lookgreatnaked.com/blog/maximizing-fat-loss-from-cardio/
- Trexler, A. E. (2018). “You might be burning less calories during cardio”. Biolayne. , 2020. Retrieved August 28. https://www.biolayne.com/articles/contest-prep/might-burning-less-calories-cardio/
- Waehner, P. (2019). “Why You Should Add Cardio to Your Workout Routine”. Retrieved August 28, 2020. https://www.verywellfit.com/everything-you-need-to-know-about-cardio-1229553