A new study shows wrist-worn heart rate monitors are actually less effective when you exercise, according a research letter published by JAMA Cardiology.
The study used an electrocardiogram (ECG) — as used in hospitals where multiple sensors are attached to the skin — as a benchmark against which four commercial wrist bands and a chest strap were compared. The Fitbit Charge HR, Apple Watch, Mio Alpha, and the Basis Peak were all put to the test. It’s the first study published in a scientific journal to compare such devices with an ECG.
The accuracy of wrist-worn monitors was found to diminish with exercise and was best at rest. The degree of accuracy also changed with the intensity of exercise: running at 6 mph, the Fitbit Charge HR underestimated heart rate by over 6 beats per minute (bpm) on average, at a more moderate 2 mph the Basis Peak actually overestimated it by around 9 bpm.
Overall, Apple came out as a joint winner with a 91% “agreement” with the ECG, tying with the Mio Fuse. The Fitbit Charge HR came out at 84%, and the Basis Peak at 83%. That’s good news as Apple is marketing the Watch Series 2 — now with built-in GPS — as the “superior sports watch”, with its own “extensive” workout app. But for those who are serious about accuracy, the results of the study show that commercial fitness bands are no substitute for a chest strap-based monitor, which had a 99% accuracy score.
What’s less clear is how obesity affects the accuracy. “I bet you they will be less accurate in people who are overweight, people who have poor circulation, people with high blood pressure,” Cleveland Clinic heart surgeon Dr. Marc Gillino told Forbes. The study concluded BMI did not influence accuracy, but then again it only examined healthy adults.
Fitness tech as a coach
Personal tech for fitness is going beyond measuring the heart rate and the length of your run, with devices now so small you might forget they are there. The Financial Times this week reviewed the Lumo Run, a US$99 sensor that clips to the back of your shorts, and the Milestone Pod, a US$25 disc that you add to your trainer. The idea is to analyse your running form through core body movements and offer personalised coaching.
Between them they record a total of 15 metrics, including cadence (steps per minute) — the most common metric used to measure running form — from which the Lumo Run can then prescribe corrective exercises personalised to you. The Milestone Pod also measures ground contact (the average time your foot spends on the ground for each stride). The less time your foot spends on the ground, the better your performance.