Is Functional Threshold Power Interchangeable with the Maximal Lactate Steady State in Trained Cyclists?
Link to research paper
What is anaerobic/lactate threshold and why does it matter?
Anaerobic threshold, also sometimes referred to as lactate threshold (these two terms are somewhat interchangeable, but for the purposes of this discussion, they will mean the same thing), is a critical concept for an endurance athlete to understand. Before I talk about what anaerobic/lactate threshold is, let’s discuss the absolute basics of energy metabolism.
Energy is produced in the body via aerobic metabolic processes (with oxygen) and via anaerobic metabolic processes (without oxygen). Metabolic process take place that have the ultimate outcome of producing adenosine triphosphate (ATP). This ATP is used to fuel muscle contraction, which is the basis of all human movement. We have a very small amount of ATP stored in the human body, and this small amount of ATP fuels short bursts of very intense activity. We also have small amounts of Creatine Phosphate, which serves to help replenish ATP stores quickly during very short, intense activity. Beyond these two pathways, we primarily produce ATP through carbohydrate metabolism and fat metabolism. Carbohydrate metabolism is mostly anaerobic and fat metabolism is aerobic. The higher the intensity of exercise, the more one begins to shift towards carbohydrate metabolism (anaerobic processes) to fuel the activity.
Anaerobic/lactate threshold is essentially the tipping point between producing energy from predominantly aerobic metabolism and predominantly anaerobic metabolism. Go above your anaerobic threshold and fatigue follows rather quickly. Why is this tipping point referred to as the anaerobic/lactate threshold? Well, when an athlete exercises above his/her threshold, anaerobic metabolism is the primary means by which energy is produced and lactate tends to accumulate in the blood very rapidly. What is lactate you might be wondering? It is a metabolic by-product of carbohydrate (anaerobic) metabolism. Despite what you may hear about lactate, it is actually helping us fight fatigue, not causing it. Many people are under the misconception that the build-up of lactate (you may also hear the term lactic acid, which is technically not correct as lactate is what is produced in the human body) causes that “burning” sensation in the muscles when exercising hard. It is actually not lactate at all! Let me describe what really happens when you cross over the anaerobic/lactate threshold in the next paragraph.
Another by-product of energy metabolism in the body is that of hydrogen ions (H+). These hydrogen ions are acidic and cause a drop in blood/muscle pH if they accumulate too rapidly. Luckily, our body has many defense mechanisms in place to help buffer this potential drop in pH. The formation of lactate is one of these buffer mechanisms! As exercise intensity rises, more and more hydrogen ions are produced. When exercising in a very aerobic state, the body can handle the amount of hydrogen ions that are accumulating, but when exercise intensity is high enough, hydrogen ions accumulate more rapidly than they can be buffered. This rapid accumulation of hydrogen ions (lactate also rises rapidly in the blood as hydrogen ions accumulate rapidly) is what causes muscle fatigue as the hydrogen ions interfere with enzymes and binding sites that allow the muscles to contract normally. Anaerobic/lactate threshold is simply the intensity at which hydrogen ions (and lactate) accumulate too rapidly in the body, thereby inducing a rather quick onset of fatigue when crossed.
Now, why does this matter to you as an endurance athlete. First, we know through research that an athlete’s threshold is one of three major predictors of endurance performance (VO2 Max and movement economy/efficiency being the other two). As threshold improves, so does the likelihood of better performance (i.e., faster times). Second, the definition of one’s threshold states that this is the maximal exercise intensity that can be sustained for approximately one hour. A lot of endurance events take longer than an hour to complete, therefore, maximizing one’s threshold is essentially like maximizing the ceiling within which one has to exercise at in a race. For those that are familiar with VO2 Max (the maximal aerobic capacity of an athlete), think of VO2 Max as the athlete’s engine and anaerobic/lactate threshold as the highest gear that the athlete can sustain for a reasonable amount of time (in this case, 1 full hour). Think of it this way too: Two athletes racing a marathon may have the same VO2 Max, but the athlete with the higher anaerobic/lactate threshold is much more likely to be the winner as he/she can exercise for longer at a higher pace/intensity than can the other athlete with a lower threshold.
If you are still in need of more on this topic in order to wrap your mind around it, click on the following video link to see a video I share with my athletes before they embark on a test to determine their threshold fitness: https://www.screencast.com/t/l46lv1wXjBI
How does one go about testing their threshold?
It’s one thing to know about threshold, but it’s another thing entirely to be able to accurately and reliably testone’s threshold fitness. Luckily, in today’s technology-friendly world, testing one’s threshold fitness has never been easier. The advent and ease of accessibility to a power meter has also made this test even more easy to conduct amongst amateur and professional athletes. For the purposes of the rest of this discussion, I’ll refer mostly to testing one’s threshold on the bike, referred to as Functional Threshold Power (FTP), as this is where it’s most common to test for threshold power, but know that testing threshold fitness is important in swimming and cycling as well.
On the bike, testing for one’s Functional Threshold Power (FTP), is as simple as doing a short (albeit hard) test on your bike with a power meter. One of the more popular testing protocols is one developed by Hunter Allen and Andrew Coggan. It is an hour-long protocol that consists of the following:
-20-min at self-selected easy intensity
-3 x 1-min fast pedaling accelerations with 1-min recovery at self-selected easy intensity
-5-min at self-selected easy intensity
-5-min time trial (at roughly estimated 20-min time trial intensity)
-10-min at self-selected easy intensity
-20-min all-out time trial
The average power from the 20-min time trial is multiplied by 0.95, giving you an estimation of one’s 60-min threshold power. This number is then incredibly useful as it helps determine training zones and can be used as a way of tracking threshold fitness over time.
However, a good researcher, and hopefully a good coach, will tell you that two things matter when it comes to test protocols:
Validity refers to how accurate a test is in determining the TRUE value of whatever you are trying to test. In the case of an FTP test, a valid test would be one that gives you an accurate and true representation as to what your 60-min threshold is if you were to actually go as hard as you could for 60-minutes. For example, if I did an all-out 60-minute time trial and got an average power of 300 watts, I would want a valid FTP test to also calculate my threshold as pretty darn close to 300 watts without me having to do a 60-minute time trial.
Reliability refers to how good a test is at giving you the same number over and over again if you were to do the test many times in a row. In the case of FTP testing, reliability here has more to do with the consistency of the environment within which the test is done than it does with the test itself. In other words, an FTP test should be done in as close to the same environment and conditions as it was done in the past. It should be done on the same bike, on the same indoor trainer or outdoor route, and ideally in the same temperature and climate so as to increase the reliability of the test.
When developing tests, researchers usually want to establish the validity and reliability of the test before they say it “works”. In the case of the popular FTP testing protocol created by Hunter Allen and Andrew Coggan, I want to know as a coach that this test is valid and reliable. The test should be reliable if done the exact same way and under the exact same conditions every single time. But, what about its’ validity? In order to determine this, it has to be compared to a gold standard test. Lucky for you, I came across a recent research study that aimed to do just this, determine the validity of the most popular FTP testing protocol out there!
What did the researchers study?
Researchers enlisted 15 cyclists and had them perform the following tests across multiple days:
1. The Allen and Coggan FTP Test (20-min time-trial to estimate threshold power)
2. Constant load tests to determine true lactate threshold by measuring lactate in the blood
Researchers then compared the estimated threshold with the true measured lactate threshold.
What are the major findings?
Essentially, the Allen and Coggan FTP test-estimated threshold power correlated almost perfectly among the 15 cyclists when compared to true measured threshold power. The correlation between the two tests was r=0.91 (r=1.0 would be a perfect correlation). The researchers concluded that the Allen and Coggan FTP test was a “noninvasive and practical alternative” to determine threshold in cyclists.
What do these findings mean to YOU as an endurance athlete or coach?
These findings are exciting for me as a coach as it gives me a better sense of security in using this test to estimate threshold power for cyclists and triathletes on the bike! Determining threshold fitness is important for an athlete and is just as important for me as a coach when working with athletes. Ultimately, I would aim to include only tests of fitness that have been validated against their gold standard, and the research here supports the Allen and Coggan test as a valid test for determining true bike-specific threshold power.
I will say that this study conducted by the researchers was rather small (n=15 cyclists), so the results should be taken in context and consider that larger samples may show us something slightly different. However, the correlation between the two tests in this study were so close to perfect, that I would be hard-pressed to imagine that the findings would be dramatically different if this study had been done in 200 cyclists as opposed to just 15.
If you already use the Allen and Coggan test, whether as a coach or as an athlete yourself, know that this is a great test for determining threshold power! However, keep in mind that you MUST perform the test in its entirety, including the warm-up exactly as prescribed, as this was the exact protocol that was validated in this study. The researchers even discuss this in the paper and mention that when the test is used without the full warm-up, research has shown that the 20-min time trial represents closer to 90% of one’s true threshold as opposed to 95% of one’s threshold when done correctly with the full warm-up.
In conclusion, the Allen and Coggan FTP test is a valid test for determining threshold power in cyclists and triathletes, however, be sure to perform the test exactly as prescribed, including the full warm-up, in order to get the most valid estimation of you or your athletes’ threshold power outputs.
Happy training and racing!
-Ryan Eckert, MS, CSCS
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