During a sport workout your body builds lactic acid which is then removed by your tissues. At a certain amount of stress your body is no longer able to process all of the lactic acid it produces, thus accumulating more and more of it. The point where more acid is produced than removed is called “lactate threshold”.
The lactate threshold marks our starting point to derive your training heart rate zones from, so you should update it frequently. It’s also important to note that the value is specific to each sport, so it has to be determined separately for biking and running.
There are two ways to determine your lactate threshold: