Overview
- The Florida International University study, published Tuesday, had 58 adults pedal a recumbent bike while researchers compared Apple, Garmin, Samsung and Fitbit calorie estimates with a metabolic analyzer.
- Across devices typical errors ran about 15 to 25 percent versus the lab measurements and for some people with higher body fat the watches were off by 50 to 100 percent or more.
- The magnitude of error rose as body fat increased and estimates were least accurate above roughly 35 percent body fat, suggesting bias tied to wearer physiology.
- Brand performance varied: Apple showed the smallest average error, Garmin and Samsung tended to overestimate more, and Fitbit produced inconsistent outliers including implausible readings far above the lab values.
- Researchers advise treating smartwatch calorie counts as rough upper‑bound estimates, relying instead on heart‑rate, duration and trend data, and call for broader studies and more transparency about proprietary algorithms.