Lactate threshold (LT) and functional threshold power (FTP) are NOT the same thing, people! I feel better now that I got that off my chest :-).
What is Lactate Threshold?
Lactate threshold is determined by a blood lactate laboratory test (example in the image above) and is the point at which lactate begins to increase exponentially in the blood stream during said test. Lactate threshold can also be seen as the inflection point on a line graph where the blood lactate concentrations are plotted for an athlete undergoing said test…
As you can see from the above image, there is a clear inflection point where lactate begins to increase exponentially (11.8 mph for this runner) and does not stop increasing until the athlete fatigues and the test stops. So, when this athlete is running slower than 11.8 mph, they are said to be “below lactate threshold.” Their cells are producing lactate still, but they are able to use it efficiently and it does not build up in the blood stream. When the testers increased the treadmill speed to 13 mph, the athlete was pushed “above lactate threshold” and their bodies began to produce even more lactate to meet energy demand. Their cells are unable to clear the lactate efficiently at this intensity which causes an increase of lactate found in the blood stream. As the testers increase the treadmill speed further, more and more lactate accumulates.
Remember, when lactate is used for energy, hydrogen is produced as a byproduct. Hydrogen lowers the pH of our blood and causes acidosis (burning) in our muscles. When acidosis gets to a point, the athlete must reduce their output as the pain and fatigue is too great to push any further. This is an important number for athletes to know because it precisely tells them what point they can push to and be able to sustain it for a long time without too much risk of fatiguing early (think of an Ironman triathlon). However, blood lactate tests are expensive, invasive, and aren’t really necessary with the advent of the power meter.
What is functional threshold power?
Functional threshold power (FTP) is the maximum power output an athlete can maintain in a quasi-steady state without fatiguing for 1 hour. FTP is, in my opinion, is a better way to analyze current fitness and improvements because it is more readily available to the athlete, isn’t invasive, and can be repeated multiple times for FREE! More about FTP here.
How did FTP and LT become confused to mean the same thing? Because your maximum effort for 1 hour is commonly the same as your lactate threshold. Dr. Andy Coggan realized this so he came up with the FTP concept and simplified things for everyone (yippee!). However, your FTP is not your LT and your LT is not your FTP, got it!?
So, to recap: what is the difference between lactate threshold and functional threshold power? LT is the point at which lactate increases in the blood stream exponentially whereas FTP is the maximum effort an athlete can maintain for 1 hour without fatiguing.