Overview
- The Florida International University study, published Thursday in PLOS One, compared Apple Watch Series 8, Fitbit Sense 2, Samsung Galaxy Watch 5 and Garmin Forerunner 955 against a COSMED K5 respiratory gas analyzer and found median percent errors of about 15 to 25 percent.
- Device performance varied: Garmin and Samsung tended to systematically overestimate energy expenditure, Apple tracked closest to the reference, and Fitbit produced extreme outliers that included seven readings above 450 percent of the reference.
- Higher body fat percentage was clearly linked to larger percent errors across all tested brands, meaning people with greater adiposity saw the biggest inaccuracies.
- The test used 58 predominantly Hispanic adults in a single recumbent cycling protocol with older watch models from 2022–2023 and with participants wearing multiple devices, so results may not apply to running, strength training, other populations, or newer firmware and models.
- Researchers say users should treat on‑watch calorie numbers as rough guides, follow long‑term trends or heart‑rate training zones instead, and note that small daily errors can add up to significant weekly differences that could affect weight-management decisions.