Wrist vs Chest based heart sensors: which is better?
Whilst wrist-based sensors offer convenience, does this come at the sacrifice of accuracy?
🤓Firstly, both wrist and chest straps work in different ways:
📈Chest straps use electrocardiography to measure the heart’s electrical activity.
📉Wrist sensors found in GPS & Smartwatches use optical heart rate sensors and measure the amount of light that is scattered by the blood flow of the skin & convert this to a heart rate via a process called Photoplethysmography (PPG).
Which is more accurate?
🎯A 2017 study found that a Polar H7 chest strap was 99.6% accurate when tested against an ECG. (Gillinov 2017)
🎯A 2019 study (looking at Apple Watch & FitBit Charge 2), found accuracy varied from +/- 1% to as high as +/-13.5%, with the Apple watch faring more accurate. This study also found increasing inaccuracy as exercise intensity increased, likely due to the faster arm movement that accompanies faster running speeds.
🎯Additionally, a 2020 systematic review by Zhang et al found the average difference of wrist-based sensors to be:
-1.64 to +0.83 bpm difference during sleep
-0.02 to 0.00 bpm during rest, so pretty accurate here!
-1.60 to +0.58 bpm during treadmill activities (walking & running) which is not a great difference
Larger differences were found in resistance training (-10.46 to -4.07 bpm) &cycling (-7.24 to -1.87bpm).
Unfortunately for consumers, watch brands will not release their data on the accuracy of their wrist-based sensors, and there can also be variation in the accuracy between individuals.
🔑So in conclusion, wrist-based sensors can be fairly accurate (within a few beats per minute) and will suit most runners, but if you want PRECISE readings then a chest strap is the way to go!
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Gillinov S, Etiwy M, Wang R, Blackburn G, Phelan D, Gillinov AM, Houghtaling P, Javadikasgari H, Desai MY. Variable Accuracy of Wearable Heart Rate Monitors during Aerobic Exercise. Med Sci Sports Exerc. 2017 Aug;49(8):1697-1703.
Pasadyn, S. R., et al. (2019). "Accuracy of commercially available heart rate monitors in athletes: a prospective study." Cardiovasc Diagn Ther 9(4): 379-385.
Thomson, E. A., et al. (2019). "Heart rate measures from the Apple Watch, Fitbit Charge HR 2, and electrocardiogram across different exercise intensities." J Sports Sci 37(12): 1411-1419.
Van Hooren, B., et al. (2020). "Real-time feedback by wearables in running: Current approaches, challenges and suggestions for improvements." J Sports Sci 38(2): 214-230.
Zhang, Y., et al. (2020). "Validity of Wrist-Worn photoplethysmography devices to measure heart rate: A systematic review and meta-analysis." J Sports Sci 38(17): 2021-2034.