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Chest strap or wrist-based heart rate measurement?

We shed light on another big question with the spread of wrist-based heart rate monitors: which one should we choose? Should we stick with the old-school chest strap or buy a more comfortable wrist-based device?

For most athletes, traditional heart rate monitors are a pain in the ass: despite the clean design and ample creaming, the scar formed from use in the place of the chest strap speaks for itself. Although these electrodes mounted on the chest provide valuable information for training work, the discomfort caused by wearing the chest strap discourages many athletes from using it, as accurate heart rate measurement is not worth it to them.

New wrist-worn devices have attempted to overcome this problem. Garmin was the first to solve heart rate measurement without a strap with the Forerunner 225 released in 2015, which used LED sensors on the back of the watch face. This was followed by a number of other brands, including Polar, Apple and Fitbit, who touted freedom from the chest strap. Of course, it sounded too good to be true, and the latest data backs it up. According to the results of a study conducted by the University of Wisconsin, heart rate data measured from the wrist is less reliable than that measured from the chest.

In the experiment, the subjects were measured simultaneously with an ECG and a wrist-based monitor while at rest and while moving. The researchers saw that the monitors were within 5 beats of the ECG at rest, but during exercise, the data measured on the wrist differed by up to 20-40 beats within 1 minute. At any given moment, the displayed result can be anywhere from perfectly accurate to quite a bit low or quite high, according to Lisa Cadmus-Bertram, the head of the research. For triathletes and other endurance athletes, this is important because they only occasionally glance down at their watches while racing. So if you calculate based on when the result is inaccurate, you can significantly influence the competitor's mental state in the wrong direction.

According to Dr. Michael Emery, medical director of the Center for Cardiovascular Medicine, these inaccuracies are a serious inconvenience. "For those athletes who are really trying to set up their training program based on objective testing, if the heart rate monitor doesn't help them stay in the right zones, then it's not helping them train accurately for that athlete's level," says Emery. At worst, inaccurate information can be fatal for some athletes with heart disease.

"From a medical perspective, if we tell a patient to keep their heart rate in a certain range, either empirically or based on a stress test," says Emery, "it's possible that they're working in a heart rate range that's not appropriate for their medical condition, simply because , because the monitor was inaccurate."

So what can an athlete do? It depends: for casual heart rate monitoring, the Fitbit or Apple Watch might be fine. The heart rate data provided at rest can still indicate overtraining or undertraining by showing full weekly trends. But when it's time to train, both Emery and Cadmus-Bertram recommend using a chest strap. "For those who really care about accuracy," says Cadmus-Bertram, "it's probably worth sticking with the old chest strap."

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