In one sentence
The calories-burned figure your watch or band reports, which VT keeps as the device's number and does not use for anything that involves food.
Why it is kept
It is a series people have followed for years, and as a trend on one device it says something about how much you moved. It is also the figure that sits beside the energy-sources split on the activity sheet, where it carries the device's error.
Why it is not used
Because it is not a measurement. A wrist device estimates energy from heart rate, movement and your profile through a model it does not publish, and when seven wrist devices were tested against laboratory calorimetry in 60 volunteers, their heart rate came within 5 percent but their energy-expenditure error ran from 27 to 93 percent, and no device came within 20 percent (Shcherbina 2017). An error of that size is larger than any deficit a weight-loss plan would set, which is why the TDEE engine excludes device calories entirely and builds its estimate from your weight and your log instead.
What moves it
Movement and heart rate, through the maker's model; also the maker's firmware updates, a change of wrist, a loose strap and a cold day, none of which change what you burned.
How Vitality Tracker uses it
Stored as one daily total from the source you chose and charted as a trend; on the activity sheet, each session's figure is labeled with the device that recorded it. It does not enter the TDEE engine, the Vitality Score, Capacity or the Weight Loss Plan.
How far to trust the number
Estimate, with a measured error of tens of percent. Its direction over weeks on one device is usable; its level is not, and it is not a food budget.
Sources
- Shcherbina A, Mattsson CM, Waggott D, et al. Accuracy in wrist-worn, sensor-based measurements of heart rate and energy expenditure in a diverse cohort. J Pers Med 2017;7:3. doi:10.3390/jpm7020003
- Vitality Tracker, How Vitality Tracker estimates your energy expenditure, method note v1.0.