I am going to attempt to keep this short and as least technical as I can but bare with me because it is impossible to explain FTP without getting into the physiological details. The idea of this article is to give you an idea of what FTP is and why it is important for you to test for it throughout the year. I also want to get this out in the open right from the start; just because someone has a higher FTP does NOT mean they are a stronger or faster rider; it just means they have a higher FTP.
Let’s start with what Functional Threshold Power (FTP) is. The textbook (Training + Racing With A Power Meter by Allen, Coggan & McGregor) definition for FTP is “The highest power that a rider can maintain in a quasi-steady state without fatiguing for approximately one hour. When power exceeds FTP, fatigue will occur much sooner, whereas power just below FTP can be maintained considerably longer.” There is a bit to unpack there so let's get to it.
Heart Rate training has been around for decades and I assume if you are an athlete reading this article you have probably dabbled in HR training or at least have read up on Lactate Threshold (LT). As a recap basically your Lactate Threshold is the point when your body is producing more lactate than it can consume leading to lactate levels building in your blood. As the lactate level in your blood begins to rise it gets to a point where you get that burning feeling in your muscles and you have no choice but to slow down (fatigue). If you are below your Lactate Threshold your body is able to clearing the lactate at a rate that is equal to or greater than its production; meaning the muscles do not get that burning feeling from increased lactate levels. So simply think of your Lactate Threshold as a line in the sand; cross it and your body will be forced to slow down very soon; stay below that line and you are free to continue for much longer.
The definition mentions “quasi-steady state.” That is because when you are going hard you don’t just sit at your threshold the whole time you will go above that LT line a little bit causing lactate to rise in the blood which will then force you to drop below the line to allow the body to clear it by consuming it for energy. So you don’t just sit at this steady line you constantly go a little above it, a little below it, back above it, below it and so on. The definition also mentions “approximately one hour”. That is because after about an hour other things come into play that may lead to fatigue such as glycogen stores, mental fortitude, increased core temperature and a long list of other things. Now depending on the athlete and the type of training/racing they do that “approximate” can typically be anywhere from 45 minutes to 75 minutes; a pretty big window.
So why am I talking about HR when we should be talking about power? The reason it is important is to understand that the power output you can maintain at your Lactate Threshold is your FTP. A major reason why you can't produce more power is because either your body is producing too much lactate OR your body is not able to consume the lactate fast enough.
So to summarize what we have talked about up to this point is that FTP is the power you can maintain for 45 minutes to 75 minutes without your body being forced to slow down due to pooling lactate. Go above that FTP number and your body is going to be forced to slow down within minutes; stay below that number and you can continue on until something else slows you down such as lack of glucose, mental fortitude, or a coffee shop.
Now lest discuss why FTP is so important. The two most important things that FTP provides us is our training zones as well as an accurate way to track TSS (previous post). If you have an inaccurate FTP you will be training in the wrong zones as well as not having a true objective understanding of your training load. Remember from my previous post regarding TSS if you do not have an accurate FTP your Intensity Factor (IF) will also be wrong which will lead to an inaccurate Training Stress Score (TSS). Without an accurate TSS you will not truly have an objective understanding of your actual training load which can increase your chances of doing too much resulting in over-training syndrome or not doing enough and limiting your improvements. If your training zones are based off of an inaccurate FTP then you are less likely to get the desired result from a structured workout because you could be calling on different energy systems than the workout is intending to target.
Let’s take a few minutes to talk about why having CORRECT training zones is so important. For this discussion we will use the Classic Power Zones which are listed below.
As a coach when I am designing a workout I am trying to target certain energy systems which should be hit in a given training zone. As an example if you are in Zone 4 (Threshold) you should be riding that very thin line of the Lactate Threshold; that your body is producing and consuming lactate at about the same rate. If you are in Zone 5 we know that your body is creating more lactate than it is capable of consuming and lactate levels are rising in the blood. If you are in Zone 2 we know that you should be producing very little lactate.
Why is this important? Because lactate is a byproduct of using your muscles to produce energy (anaerobic system); so the marker of lactate allows us to know how involved your anaerobic energy system is at that moment. If we are doing Zone 5 work I expect the anaerobic system to be much more involved in power production than if we were in Zone 2. Our aerobic system uses lactate to produce energy; which is one reason why your breathing rate increases as your effort does. If we are in Zone 2 our anaerobic system is not being used very much therefore it is not providing enough lactate to be used by our aerobic system. To make up for the lack of lactate as an energy source our aerobic system will use fat stores as an additional fuel source. See how important these zones are; they actually mean something! Let’s take a look at our zones again adding a ‘general idea’ of the energy systems.
As a coach I am asking you to work in a given training zone because I am looking for a given response from your body; so if your FTP is wrong then your training zones are wrong. If your training zones are wrong then my workout is wrong; don’t make my workout be wrong. Below is an example of how your training zones would shift if you overestimated your FTP by just 10%.
As you can see above if I gave this athlete a workout that was targeting Zone 4 (Threshold) and he overestimated his FTP he would attempt to do that workout between 238-277 watts. Since the FTP is overestimated he would be riding above his true FTP (240) causing the lactate level in his blood to continue rising until sooner or later….POP! The athlete would have no choice but to drop the power to recover and clear out that extra lactate. The workout doesn’t get done properly, the goal of the workout is not achieved and the athlete is bummed because he failed at something he thinks he should have been able to do. If he wasn’t so egotistical and had his FTP set correctly he could have successfully completed the workout by holding 216-252 rather than attempting to hold 238-277. Mentally he would have felt better about nailing the workout and more importantly he would have gained the desired physiological adaptation we were targeting leading to a higher FTP in the future.
Lose your ego and set your FTP to what it actually is not what you wish it was. You will gain more fitness by completing the workouts the way they are purposefully designed rather than trying to “outdo” it. A lot of athletes have the idea that if they workout harder than the workout is asking them to do that it is better; they couldn’t be more wrong. The purpose of a given workout is to work specific energy systems; if you go above the target then you change the energy system required to do the work; you changed the workout.
Bottom line is your FTP is not to tell you how strong or fast you are compared to another rider. It is to properly set your training zones so you can become faster than the other riders. If you have a power meter and do not have an accurate FTP set and are not testing it regularly then you are not training properly, period. I do not care if you have a higher FTP than me. I do care that my training zones are correct so my FTP will be even higher after a few months of proper training.