The Accuracy Problem
A 2023 Journal of Sports Sciences study tested 10 wrist devices against medical-grade equipment. Heart rate: ±3-5 bpm at rest, ±10-15 during exercise. Steps: ±5-10%. Calories: off by 27-93%.
Heart Rate: Most Reliable
Stanford Medicine's 2024 study found Apple Watch Series 9, Garmin Venu 3, and Pixel Watch 2 all achieved clinical-grade accuracy at rest. During heavy wrist movement (CrossFit, kettlebells), a chest strap like the Polar H10 ($80) still wins.
Calories: The Big Lie
A 2022 JAMA study found devices overestimated calorie burn by 27% for walking and 93% for cycling. Use calorie data for relative comparisons, not absolutes. Never eat back all the calories your watch says you burned.
Top Picks
Apple Watch Series 10
Best sensor suite: ECG, blood oxygen, temperature. iPhone-only. Most accurate HR in Stanford testing.
Garmin Venu 3
iPhone + Android. Best GPS, 14-day battery, excellent sleep tracking. Best for runners and outdoor athletes.
Sources
- Bent, B. et al. "Wearable optical heart rate sensor accuracy." NPJ Digital Medicine, 2020.
- Stanford Medicine Wearable Accuracy Study, 2024.
- Shcherbina, A. et al. "Wrist-Worn Sensor Accuracy." JAMA, 2022.
- Journal of Sports Sciences, 41(8), 2023.
