Chest Strap vs Smartwatch Heart Rate: Do You Still Need a Strap?
The Two Numbers That Disagree Two devices on the same body, one workout, and two different heart rates. Runners meet this contradiction the first time they wear a strap alongside a watch during intervals. The watch is not broken. It measures a different physical signal, and that signal behaves badly in exactly the moments when precise numbers matter most. Here is the short version. Keep the watch alone if your training is mostly steady, and add a chest strap if you run intervals, chase narrow zones, lift weights, or train in the cold. An optical armband is the middle path. It measures on the forearm or upper arm, where movement interferes less, and it skips the chest band that many people dislike. Our Garmin vs Apple Watch for running comparison covers the watch half of this setup. Why The Wrist Lies During Intervals Wrist sensors shine light into the skin and read the pulse of blood beneath it. Chest straps read the electrical activity that triggers each beat, which is a cle...