Did I ever tell you that I’m a massive fan of heart rate training? No? Well I am. But there is one thing that really bugs me when it comes to heart rate training and it’s the ‘fat burning zone’. Not that the zone itself bugs me, but it’s when people big it up and get you to believe that you are going to lose weight quicker if you train in the ‘fat burning zone’. Just for the record, in my opinion….THAT IS SO WRONG!
When you train at a lower intensity the body is more likely to utilise fat as the energy source rather than glycogen (carbs). This is due to the respiratory exchange rate – the ratio of oxygen consumed to carbon dioxide produced during training. If the respiratory exchange rate is less than 1 (more oxygen than carbon dioxide) your body will utilise fat as the primary energy source. If the respiratory exchange rate is equal to or more than 1 (more carbon dioxide produced than oxygen consumed) the body will use glycogen as the primary energy source. It must be understood that either way, you are not soley using fat or glycogen alone as the energy source.
When you train at a lower work rate, the percentage of fat utilisation is greater than glycogen. At higher work rates this is switched so that glycogen is the primary energy source. When you train at lower intensities (around 50% of your max) the fat/glycogen energy ratio is approximately 60/40. However, when you increase your workout intensity this ratio changes and your body will use glycogen over fat. However at higher intesity training you still burn fat and have the potential to burn more fat than at lower intensity training.
The below is taken from an article from builtlean.com. Hopefully this will show what I am trying to say from a numbers perspective:
So here’s what the breakdown looks like assuming 30 minutes of exercise for a low vs. high intensity group. The high intensity group will likely burn double the calories as the lower intensity group, or 200 vs. 400 calories:
30 Minutes of Exercise Fat Calories Burned Glycogen Calories Burned Total Calories Burned Low Intensity Group (50%) 120 80 200 High Intensity Group (75%) 140 260 400
I train in the fat burning zone but I’m not doing this because I want to lose weight. I’m doing this because I want my body to get used to using fat as an energy source. As I am going to be racing for extensive periods of time I am training my body to use fat so that, when my glycogen stores become depleted (and I know that they will) my body will be able to make a quicker transition to using fat rather than having that ‘bonking’ feeling when my body switches over. If I wanted to lose weight I would work on buring calories not just fat. I would be pushing for higher levels of training ensuring that I burned as many calories as I could within the training time that I had.
I hope this little article makes sense to you and you get to understand that if you want to lose weight, you don’t have to get too hung up on the ‘fat burning zone’. If you want to lose weight hit that HIIT. Get the calories burned and understand that even if you are working at a higher intensity, you will still be burning that fat.
Have a fit and healthy day