That's to record and detect the heart rate. It is difficult to judge the effect of exercise with the naked eye. Only through the change of heart rate can we scientifically judge the training state of this person in the training process. Whether it is up to standard or not, keeping the heart rate between 70 and 80 is the best training interval. Too low is ineffective training, too high heart rate is harmful to health first, and then the training effect is not good, and it will also consume muscles. Therefore, many professionals rely on this to record heart rate changes, thus guiding their own training. Improve their training quality.