How does the activity calculator work?

Most of the data used by calories burned calculators has been collected by measuring the amount of oxygen consumed performing each activity. A number, called a MET (Metabolic Equivalent), is assigned to each activity to indicate its level of intensity.

An activity with a MET of one corresponds to a person'sRMR (Resting Metabolic Rate), the rate at which they would burn calories resting. Other activities are assigned MET values to indicate their intensity level relative to RMR.

For example, driving a car has a MET of two and playing water polo has a MET of ten. This indicates that you would burn twice as many calories driving a car as you would sitting still, and ten times as many playing water polo.

Based on the above, it would appear that the most accurate way to calculate calories burned would be to use the number of METs assigned to the activity you select, your RMR, and the length of time you performed the activity. However, in most cases the MET data was collected using a constant based on weight alone rather than RMR. Therefore for consistency we also use a constant based on your weight rather than RMR.

Important Technical Notes

1. Because our calories burned calculations are based on your weight and a constant rather than your RMR, you will notice that when you change the parameters for your sex, age and height, your RMR and BMR calculations will change but the calories burned calculations will not be affected.
2. Calories burned calculations include the total number of calories burned during the period of time calculated. Therefore when calculating how many calories you need or burn in a day, do not add your RMR or BMR.

Intensity Level

Our calculator uses METs, body weight and duration of activity to calculate the number of calories burned. A fourth very significant parameter is the intensity level at which the activity is performed.

We base our activity listings on intensity level whenever the data is available. For example, running is very specific and is listed at various speeds; downhill skiing is listed as light, moderate, and vigorous. Activities such as attending class and bailing hay, however, are much more general with no indication of intensity.

Intensity would obviously play a greater role in determining the number calories burned bailing hay than attending class. Considering such factors will help you understand the value of our estimates.

We are frequently asked about the meaning of terms such as light, moderate, and vigorous. While we do not know the specifics of how all of our data was collected, one common method is to simply take a group of people and ask each of them to perform the activity at light, moderate, and vigorous levels of intensity and take measurements.

Using this method the measurements are based on what the participants "feel" is the correct level of intensity. While this method may not sound very scientific, if the intensity level were measured with instruments then using the data would require the same instruments. Thus using "feel" is a more practical method of making estimates.

Very Heavy and Very Light Individuals

There is the potential for inaccuracy in calculating the calories burned by very heavy individuals. While an individual's weight is used to calculate the number of calories burned, the additional energy required for a very heavy individual to bear their own weight performing weight bearing activities is not factored into the equation. Thus the actual number of calories burned may be higher than estimated.

Conversely, when performing non-weight bearing activities, the heavy weight used to calculate the number of calories burned may play too great a role in the equation. Thus the actual number of calories burned may be lower than estimated.

Just the opposite would be true for a very light individual. Performing weight bearing activities, the actual number of calories burned may be lower than estimated; performing non-weight bearing activities, the actual number of calories burned may be higher than estimated.

Very Strong and Very Weak Individuals

There is also the potential for inaccuracy in calculating the calories burned by very strong and very weak individuals. The formulas used for calculations do not take into account your body composition (percent muscle vs. fat) and are therefore less accurate if you have a non-typical amount of muscle. This is because muscle burns more calories than fat.

A person with an above average amount of muscle will burn more calories than calculated, and a person with a below average amount of muscle will burn fewer calories than calculated.

Other Factors

Other factors that are not accounted for in the equation include:

• Your height, age and sex.
• Your efficiency of movement (e.g., how well you have perfected your swim stroke)
• The environment (e.g., running into the wind)
• The geography (e.g., running uphill)