Determining How Many Calories You Burned

Everything Else
1

Following an interesting conversation in South Carolina, I wanted to find out what is the best method of determining how many calories are burned during exercise. In order of accuracy:

  1. Indirect Calorimetry

Based on the work of Weir (1949), energy expenditure can be reliably estimated by a measure of your oxygen consumption rate and carbon dioxide production rate. Making these measurements requires wearing a portable gas analyser, which is only really possible in a lab test.

  1. Output Power

Using an ergometer, it is possible to measure the work performed during your workout; that is the energy transferred to your pedals. Since humans are not 100% efficient in converting chemical energy to mechanical energy, the uncertainty in this method lies in the estimation of your efficiency. Reading around on the web, this number seems to be between 20-25%, so to first order you can trust your calories burned based on power to within 5%. This method really only applies to cycling, though (maybe rowing?).

  1. Heart Rate

Heart rate can be used to estimate calories burned since heart rate linearly correlates with oxygen consumption (see the paragraph on indirect calorimetry). The problem here is that heart rate can vary depending on a lot of factors like emotion, posture, environment, and fitness level. Keytel et al (2005) show that you can get a better estimate of calories burned based on heart rate if you include your VO2max, if you know it. Uncertainty with this method can be as large as 20%. The advantage to this method is that you can easily measure heart rate by wearing an HR monitor, so you can estimate energy expenditure for a variety of activities (not just cycling).

2

Before anyone comments, what I meant to say was in order of precision :wink:

3

Well of course power meters also normally only guarantee errors of <1-2% depending on the product, and that when they’ve been properly calibrated and are in a normal temperature window. So that would factor in as well.

Overall I’m surprised that calorie burn from power is that accurate though.

4

Good point, Eric.
Haakonssen et al (2013) found that if you measured your gross efficiency, power meters can give you your energy expenditure to within 2% (basically the uncertainty of the power meter). Using a group averaged gross efficiency of 19%, individual errors of energy expenditure were as large as 11%.

By the way, if anyone wants to read the papers I’m citing, let me know and I’ll send you a copy.

5

I just eat iceberg lettuce and don’t worry about it

6

so do I but it is usually next to a meat patty and cheese and some condiments. I don’t think it retains it’s low cal features that way…