I hear this topic come up quite a bit, so I thought I would try and make it easier for some of you. Lactate threshold is defined as the exercise intensity at which lactate starts to accumulate in the blood stream. Without adding too much confusion with regards to what is going on at the cellular level, lets stick with how to find this necessary heart rate. We have all seen the 220- your age x the % of intensity to set that heart rate monitor of yours. This is not exact and I can give you several examples of occurences when it was off. A better , more scientific method is a lactate threshold test. This test is best done by running for 30 minutes as hard as you can. Your average heart rate for the last 20 minutes will give you this number. Now a lot of factors come into play- motivation, dehydration, fatigue,etc so you will want to attempt this test 3-4 times and you should start to see a pattern with regards to what your threshold training heart rate is. This magic training heart rate is zone 4 for all the heart rate monitor wearing fitness people out there.