Remember when the treadmill told you that you burned 250 calories after that 20-minute run?
I hate to be the one to break it to you but the machine was totally lying to you. You most likely burned much less than that.
Cardio machines like treadmills, the elliptical and the Stair Master all keep track of calories burned during a workout, but since they cannot consistently read your heart rate for the entire duration of your cardio session, they have no way to give you an accurate account of that number.
The same goes for fitness apps that track activity like MapMyRun or RunKeeper. Unless connected to a heart rate monitor, it’s impossible for an app on your phone (or any other device) to calculate how many calories you burned.
Most of the time they end up grossly overestimating your energy expenditure, which isn't a totally detrimental problem, but can sometimes lead those who are keeping close tabs on calories burned and consumed (usually as a method to lose weight) to miscalculate their overall energy balance for the day.
In order to accurately track the energy expenditure of your workouts, you’ll need to invest in a heart rate monitor tool like the Mio Alpha Strapless Heart Rate Monitor watch or the Polar RC3 GPS (a better option for runners and cyclers).
Because energy expenditure is so different among individuals, these tools allow you to enter your age, height, weight and gender—all factors that play a role in helping to calculate an accurate estimate of how many calories you’re burning while working out.
For some, keeping track of calorie intake and expenditure can be an effective weight loss tool but it’s not the best method for everyone. Before you decide to invest in a heart rate monitor and use calorie tracking as a weight loss tool, keep a few of the following concepts in mind.
It’s important to consider that calories aren’t an exact science. As noted above, you should definitely never measure your energy expenditure based off of what a machine at the gym tells you and you should also consider the calculation of your calories consumed a rough estimate rather than an exact amount.
If you use calorie counting as a weight loss tool, think of it as a guideline that will help keep you on track rather than a strict benchmark that must be adhered to perfectly.