A Cyclist’s Guide to Functional Threshold Power
Functional Threshold Power (FTP) has long been held as the gold standard when it comes to quantifying performance in competitive endurance athletes. With the cost of a power meter now well within reach for most cyclists, riders of all abilities now have the means to objectively see how their performance is improving – or deteriorating, over time. But is this measurement even important in what you personally do as a cyclist, and if so, how do you go about improving that number? In this article we’ll take a deep dive into all things FTP – what it represents, how to measure it, and how to improve it.
What is FTP?
Let’s start with the idea of a threshold. As exercise intensity rises, the increasing demand for energy means that the muscles’ aerobic energy production systems are supplemented and eventually taken over by a process called ‘glycolysis’ where carbohydrate in the form of glycogen is broken down, producing lactate which can supply the muscles with energy without combining with oxygen to do so. A byproduct of this reaction is the accumulation of hydrogen ions causing the blood to become more and more acidic to the point where further increases in intensity are unsustainable. A graph plotting blood lactate levels against some exercise intensity indicator – usually heart rate, shows an exponential increase in lactate where the body’s ability to clear out the byproducts of glycolysis is outpaced by the rate of accumulation. This point is referred to as the Lactate Threshold (more accurately ‘Lactate Threshold 2, LT2) or sometimes the Onset of Blood Lactate Accumulation (OBLA).
At LT2, blood lactate concentrations are rising rapidly corresponding to a threshold power of 260 Watts at a HR of about 156 bpm (red line on graph). LT1 is where blood lactate first begins to rise from baseline and marks the start of where glycolysis begins to supplement the aerobic energy system to replace ATP in the working muscles.
So the power you are able to produce at this threshold (LT2) would obviously be your ‘Threshold Power’. This is a level of power that you can just about sustain for a long period before rapidly increasing blood acidity means any further increase in power is unsustainable. The ‘Functional’ part of ‘Functional Threshold Power’ comes from making an estimation, out in the field, of where this threshold is based on functional testing outside of a lab environment. We estimate FTP basically by seeing what the maximum power an athlete can sustain is over a period of one hour.
How Accurate is FTP Testing?
Ideally we would just ride as hard as we could for one hour to get a true value of FTP. However, this kind of effort is something any sane cyclist would not want to do more than once, if at all. Therefore, various protocols have been developed to make testing easier including variations on a 20 minute effort test, as well as tests that ramp up resistance in incremental steps until the rider can no longer sustain the effort. Limitations in these protocols as well as variations in environmental factors mean that these tests can have varying degrees of accuracy. Indeed, it has been shown that most riders who have obtained a threshold power value functionally, can in actual fact only sustain that output for around 30-40 minutes rather than the full hour. Furthermore, there are measurable differences between the power that can be sustained when riding indoors on a stationary trainer and when outside on the open road or trail. This difference in power can be as much as 10-20% depending on individual setups as well as overall athlete level of fitness.
It should also be noted that the power threshold is not like an on/ off switch. It is not true to say that below threshold you can pedal indefinitely, and above that power level the lights suddenly go out. You are still dealing with a considerable amount of blood acidity. How long you can sustain that level of discomfort depends a lot on your mental fortitude and your willingness to suffer – working at 95% of FTP is still a hard place to be.
What’s a Good FTP, and How Much Improvement Can You Really Make?
Unless you ride and race exclusively on flat terrain, a high absolute FTP is relatively unimportant since gravity will take its toll on the heavier riders, and even those with a high absolute FTP value will struggle to keep pace with their lighter peers when the road tilts up. In this case Watts /Kilo is the more important metric. In a flat time trial however, those with more lean muscle mass and high absolute FTP will have the advantage, all else being equal. A good FTP then, is relative to a rider’s weight. Something like 4 W/Kg would be a good number to work with if you wanted to be competitive in an amateur cat 3 road race for example.
It is important to realize that there are genetic limitations to achieving a high power-to-weight ratio, and that just because someone you know of the same age has a particular FTP value, there are a couple of very good reasons why you may not ever be able to match that power in absolute terms. One reason is the ratio of ‘slow twitch’ (type 1) to ‘fast twitch’ (type 2) muscle fibers. All bodies are different and while it is possible to have some fiber type conversion with the right training, for the most part those born with a naturally high proportion of slower twitch muscles will have an advantage when it comes to sustained power output, while those with more type 2 fibers will have more high-end and explosive power. Type 2 fibers rely more on glycolytic energy production than the more aerobically efficient type 1 fibers, and hence tire more easily.
Additionally, there are body geometry factors that influence the ability to generate power sustainably. Contracting muscles cause movement around a hinge point or ‘fulcrum’, for example at the knee or the hip. Where your muscles attach to the bones in the leg matters, with those with bones attaching distally lower down the limb having a mechanical advantage – more movement for any given contractile force meaning less work over time, equaling less fatigue for a given amount of sustained power.
Does FTP matter?
Trying to stay motivated and keep on track toward your performance goals can be hard. Unless you are relatively new to endurance sports, progress can at times be hard to judge, and in this respect having an objective way to quantify your progress is invaluable. The gold standard for assessing an athlete’s level of fitness is by comparing how well you perform at threshold versus your performance at the intensity where your body is utilizing its absolute maximum amount of oxygen (VO2max). A high threshold heart rate as a percentage of maximum heart rate is an indication of a fit athlete. Note that this is a ratio, so no particular units are implied – in cyclists we look at power output at threshold versus power at VO2max. In runners or swimmers it is generally expressed as pace. As training progresses, it is hoped that we see an increase in this percentage value, so while many athletes have reached, or come close to their genetically limited ceiling as far as VO2max goes, there is most often room to push up threshold power /pace with the fittest among us achieving a ratio of 85-90% of VO2max.
As with all training, the more you do something, generally the better you get at it. So, training specifically at or around your threshold power will hopefully give you a better threshold power. This is very important if you are a triathlete, marathon runner, or most of your bike racing is doing longer time trials. However ,in an average mass-start road, gravel, or mountain bike race, the ability to put out a hard sustained effort for an hour plus, doesn’t always get the job done. Unless the course involves longer climbing sections, or you find yourself in a solo breakaway, other performance metrics often carry more weight. Leaving aside your ability to execute a tactically smart race, being able to hang on to very hard but short surges in pace or put down a strong sprint after many miles at zone 2 or tempo pace, is often much more important than having a high FTP.
Bike racing is very different to running marathons or competing in a triathlon. The intensity demanded can vary rapidly from one mile to the next, and so consequently you need to hone all of your energy producing systems, not just threshold power. The good news is that if you have approached training for a high threshold power in a methodical, structured manner, you have most likely made big improvements to your 5 minute power and even your 5 second power.
How to Raise FTP Through Training
To achieve adaptations to a specific body energy system, training specificity and progressive overload are the key concepts. At threshold power intensities, the body is still using a combination of oxidative and glycolytic processes to replenish ATP in the working muscles, and training right at or close to your current threshold power will elicit efficiency improvements in both of these systems. As improvements are made, the intensity needs to increase, applying just the right amount of stress so that the body continues to adapt.
At threshold, the buildup of lactate and associated byproducts in the working muscles is increasing at a rapid rate, and while it is possible to build up a tolerance, both physically and psychologically to this increasing blood acidity, a better approach is to improve the body’s ability to flush, or ‘shuttle’ these metabolites from the working muscle fibers. So-called ‘lactate shuttle’ intervals work by spiking muscle lactate concentrations with brief bursts of power above threshold before settling straight into periods at just below threshold where the work of removing the acidity takes place. As lactate shuttling efficiency improves, we progressively overload the system with incrementally more challenging intervals, pushing up threshold power further.
Lactate shuttle intervals work by first spiking lactate levels with short bursts of power above threshold, and then attempting to clear the lactate and associated byproducts during a longer effort at sub-threshold power.
While lactate shuttle style intervals have been proven to be highly effective, two additional approaches to FTP improvement are worth mentioning here. Firstly, by improving aerobic fitness with plenty of zone 2 riding, we can effectively shift the lactate level /workout intensity curve on the graph to the right. Having a highly trained aerobic system means that the contribution of glycolysis to energy production happens at a higher intensity and therefore the onset of blood lactate accumulation (OBLA) is delayed. Secondly, there are instances where athletes have a high FTP relative to their VO2max but with a low absolute FTP value. In these cases it can be that there is plenty of room for improvement in maximum oxygen uptake, and training should focus on ‘pulling up’ FTP by doing more VO2max focused intervals.
In conclusion, while FTP might not be as important to you as a cyclist than to your marathon running, or time trialing brethren, it is an important metric for gauging your own fitness level. Test for FTP at the beginning of a training block and test again at the conclusion to get an objective indication of whether your training has been effective. Specifically improve your FTP by doing lots of work at or around your threshold power, and include a lot of ‘lactate shuttle’ type intervals. Training specificity and progressive overload are key to making improvements.
