Join Date: Dec 2010
Location: Bend, Oregon
Bikes: Motobecane Fantom Cross Pro; Motobecane Nemesis Pro
The facts about calorie calculation and Garmin
I found about how Garmin devices calculate calories.
Garmin device coupled with HR monitor
Without the use of a HR monitor
2) Firstbeat Algorithm (Current – 2nd Generation): The Firstbeat algorithm is the most accurate Garmin device calorie measurement that can be done without external testing. But it’s actually not developed natively by Garmin. It’s developed by a Finish company (Firstbeat Technologies) that has its roots in calculations around Olympic athletes, specifically Nordic skiing. Their calculation uses user inputted variables including gender, height, weight and fitness class. It then combines this data with heart rate information from the ANT+ heart rate strap. Specifically, it evaluates the time between heart beats (beat to beat) to determine estimated MET (Metabolic Equivalent), which in turn is used determine actual work expenditure.
This makes the system one of the more accurate non-invasive options (read: doesn’t require a laboratory), within about 10% accuracy. Firstbeat has published a fascinating white paper detailing the technology and accuracy rates. This little snippet below though helps to show where the technology lies accuracy-wise – with it being right in the upper-middle compared to full-board lab operations on one end, and ‘distance/time’ calculations on the other end (click below to expand picture).
Finally, this metric also ‘learns’ you as an athlete on a given device. Meaning, over time it has a weighted algorithm to note changes in your fitness level and adjust calorie burn accordingly. I asked how ‘friends and family’ using a device might impact this. They noted that a single one-time use wasn’t weighted heavily enough to make a difference, but that obviously a couple sharing a single device would see less accurate results (both due to the profile information being incorrect 50% of the time, as well as the ‘learning’ aspect being off). It also should be noted that the second-generation of the Firstbeat algorithm is only applicable to running currently, and isn’t used in the cycling products yet.
5) Speed/Distance Algorithm: This is the most basic method of determining calories, as it is only used when a heart rate strap is not enabled/used (default). Given the lack of heart rate data, the unit will simply use speed/distance, as well as the weight you entered in the device setup. The reason this is less accurate (65-80% accurate) is that it can’t differentiate how much effort you’re expending to travel a given distance – which while less important for running, is quite important for cycling. For example, if you’re coasting down a 7 mile descent, you’ll burn virtually no calories compared to ascending the same mountain. This speed/distance algorithm does not consider or evaluate the impact of elevation change – primarily due to concerns the team had about relying on GPS-based elevation to determine calories. They also reasoned that while the Edge units had barometric altimeters, it was better to focus on heart-rate based calorie burn, as opposed to simply expanding the ‘guesstimate’ that the speed/distance algorithm is. Finally, note that if you wear a heart-rate monitor/strap – speed/distance are ignored, and instead one of the other above (more accurate) methods are used.
The highlighted section in the image is the method used when using a HR monitor.
Seems there is A LOT of misinformation about the calorie function on Garmin devices so hopefully this will help a little.