We’ve all seen the graph on the treadmill showing where the “fat burning zone” is, but as usual things are oversimplified and lead to misunderstandings which lead to unnecessary time wasted in the gym. Let’s look at the science!
Low intensity cardio burns more fat during the Workout
It is very common for bodybuilders to choose low intensity cardio such as walking on the treadmill for 1-2 hours. The reason behind this is that you will burn proportionally more fat DURING low intensity cardio compared to high intensity cardio. For example if you burn 500 calories from low intensity cardio perhaps 250 of those will be from fat whereas if you burn 500 calories high intensity cardio perhaps 150 of those will be from fat (these numbers are just examples).
To really optimize fat loss, we need to look at the bigger picture. The body is smarter than you think. How does the body respond AFTER your workout? Studies have measured how what energy sources your body uses after various workouts and results are surprising.
Low intensity cardio burns less fat after the Workout
Your body actually COMPENSATES for the fat burnt during low intensity cardio by burning LESS fat more carbohydrate sources of energy (called glycogen) throughout the rest of the day.
Choose the Right Type of Cardio for Your Goals!
So the most important question is then, which workout burns the most calories? The answer? High intensity of course! If working out isn’t your career, you only have limited time to do so. If you have 30 minutes to spare on cardio and your goal is fat loss, spend those 30 minutes running or doing another type of high intensity cardio.
High Intensity Cardio Requires More Recovery
Keep in mind, however, that high intensity cardio generally is more taxing on the body, requiring more recovery and therefore you need to time it in a way to allow your muscles to recover if you also are hitting the weights.
So in the end the ratio of fats to carbs burnt will be the same no matter what type of cardio you do. Therefore, the common gym-goer is better off running and jogging as you don’t need to waste hours on the treadmill and you will burn the same proportion of fat anyways, and burning more calories in less time.
1. Spriet LL. Regulatory mechanisms in the interaction between carbohydrate and lipid oxidation during exercise. Acta Physiol Scand. 2003 Aug;178(4):443-52.
2. Melanson EL. Exercise improves fat metabolism in muscle but does not increase 24-h fat oxidation. Exerc Sport Sci Rev. 2009 Apr;37(2):93-101.