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.