Science has shown that runners get equally fit whether they exercise slightly above, precisely at, or slightly below the heart rate that is associated with a blood lactate concentration of 4 mmol/L in their designated moderate-intensity workouts. In other words, close is good enough when it comes to determining the lactate threshold heart rate, and it so happens that it’s possible to get close to the scientific standard for identifying the lactate threshold with do-it-yourself alternatives to lab-based testing.
