Lactate Threshold - Lactate inflection point (LIP), is the exercise intensity at which the blood concentration of lactate and/or lactic acid begins to exponentially increase. Often expressed as 85% of maximum heart rate or 75% of maximum oxygen intake.
Lactate threshold is the point at which your body begins to have trouble dealing with all of the pressure of the current exercise. This level is important to know because this is an intensity that you can determine different levels of training from. You can be tested through a blood test whereby you exercise with increasing intensities until exhaustion. Every three to five minutes your blood is tested to determine the acid in the blood. However, most of us do not have the money to go and have this tested this way.
Most of the time you can determine your lactate threshold by doing an all-out exercise for several minutes, either running, biking, or swimming. You then take about 5% off of the total time or power and you have your lactate threshold to determine your training intensities. If you always exercise at your lactate threshold level you will not see as much progress in your overall fitness as if you vary your workouts to include some lower aerobic exercises combined with higher intensity workouts.
The optimal situation is to gather as much data as you can so as to improve your lactate threshold. You want to try and raise your threshold so that you can exercise longer at higher intensities. If you're looking to improve your overall triathlon races, you will want to determine your lactate threshold and then find a plan that will work with the intensities you have determined from this testing. You can look at cycling programs like "Spinervals" that will give you a test to determine your threshold for power and heart rate. You can then utilize the plans that Spinervals has to help you become an overall better cyclist.
You will want to retest for your lactate threshold every 6 to 8 weeks to determine how you are getting more fit. Therefore, you want to make sure that whatever test you use is repeatable. For cycling, I use my indoor trainer that has a power meter (power tap) in the rear wheel. There are several factors that lead me to use this type of testing. I live in a cold weather climate during the winter so for 5 months I will not ride outside. Traffic conditions can cause me to slow down during the 15 miles all out test. Wind conditions can vary from day to day where I live thus causing issues. I believe this is a very repeatable way to test for lactate threshold.
I determine my run threshold by running on the treadmill at my gym. Once again, I do not have to worry about weather or conditions to change my running patterns for this test. I know that this is not fun nor is it necessarily the best way, but it is repeatable from one day to another day 6 weeks later. Swimming, obviously, takes place in my local pool. Again, this is repeatable from one test to the next.
One caution, if you go into a day that you are to test and you feel sick, it is best to skip the test to a later date. Doing these tests while tired or sick will not lead to the best results.