You may have heard it said over the years that if you want to lose weight and burn body fat you had better not work at an intensity that is higher than 70% of your maximum heart rate (your maximum heart rate is approximately 220 minus your age). And for years many of us have bought into that. The instant we found ourselves working at a higher intensity we backed off fearing that we might not shed unwanted pounds. The truth is that while we may burn calories from fat at a lower intensity (50 to 70% of MHR) at the time of the activity, we will burn more calories in general by working at a higher intensity (75 to 90% of MHR). What’s even better is that the longer we work out at a higher intensity the more calories we burn after the fact – the AFTERBURN!
The way it works is this: When we work hard enough that we are really huffing and puffing we create something called an oxygen deficit. That deficit is going to have to be paid back later on and that’s called Post Exercise Oxygen Consumption or PEOC.
For Example: If you exercise for 60 minutes at a moderate to vigorous intensity you will almost double the PEOC that you would achieve exercising at the same intensity for 20 to 40 minutes. That means that you will be burning calories both while exercising and after you have stopped exercising. If you don’t have 60 minutes don’t worry. If you work harder for a shorter duration of time (say an 8 or 9 out of 10 on a scale of perceived exertion) you will still create a hefty oxygen deficit.
How long does the effect last? A study at the University of Missouri showed that after vigorous exercise calorie expenditure increased for up to 48 hours! Individuals (assume they are of average weight; 150 lbs) running at about 80% of their MHR for one hour burned 600 to 700 calories at the time of the activity. They went on to burn around 15% more calories during the next 48 hours. That’s around 100 extra calories while they were doing NOTHING! So if they work out at that intensity 3 times a week they will burn 1950 calories while they are exercising and then another 300 calories doing nothing. That’s a total of 2250 calories in one week! That is slightly over 1 lb. of fat in two weeks. Of course if they include weight training in their program that will increase the amount of fat burned as well by increasing their lean muscle mass (muscle loves to snack on fat!).
What about those of us who are not quite ready to exercise at 80% of our MHR for an hour? We can do 2 shorter sessions and still get a great afterburn!
The bottom line? The higher our training heart rate, or level of exertion, the more calories burned altogether. After all, body fat is the primary source of fuel while we are sleeping but hopefully none of us would choose sleep as a viable option for either our weight loss or fitness goals.
So…Get that engine revved up nice and high and reap the benefits of the AFTERBURN!