We tested and recommend all of the heart rate monitors below, which do a pretty impeccable job. Heart rate zones: If someone tells you they’ve been doing 80/20 training, they’ve been doing heart rate zone-based workouts. Maximum heart rate: Some monitors can inform you of your maximum heart rate, which is the number of beats your heart can reach during exercise. Heart rate variability: Heart rate variability measures the intervals between heart beats and is measured in milliseconds. A low resting heart rate is associated with athletes, because the heart has been trained to be more efficient.