At Working Triathlete, we’ve moved away from traditional methods of estimating functional threshold power (FTP) and instead prioritize more insightful and individualized approaches. For athletes seeking the most comprehensive data, we use INSCYD testing. For those looking for a simpler or more cost-effective option, we often prescribe critical power (CP) testing—typically through two maximal efforts, such as a 3-minute and a 12-minute test.
While CP and FTP are often similar, CP is a more precise and physiologically grounded metric. It reflects your unique power-duration relationship and allows us to define more individualized training zones. More importantly, it offers deeper insight into your rider profile—highlighting whether your current fitness resembles that of a crit specialist, climber, time trialist, or long-course triathlete. This helps guide not just how hard to train, but how to train, aligning your workouts with your physiology and goals.
What is Functional Threshold Power (FTP)?
At the risk of oversimplifying, FTP is the maximum power you can put out for 60 minutes. Most athletes/coaches use it to calculate intensity zones. In the traditional five-zone intensity model, FTP falls in Zone 4, and your other intensity zones are calculated in relation to it. Because riding all-out for an hour is brutal, FTP is commonly calculated via tests in training wherein you ride as hard as you can for a shorter period and then calculate a percentage of that average power output to estimate your FTP. The most common protocol is doing a 5-min blast and then riding as hard as you can for 20 minutes, multiplying your average power over the 20-min effort by 95%. Ramp tests are another way of estimating your FTP.
Traditional FTP testing is a practical way to estimate your anaerobic threshold—also referred to as LT2 or VT2—which represents the intensity at which lactate begins to accumulate rapidly in the blood. However, it’s important to recognize that FTP is typically defined as the maximum power you can sustain for 60 minutes. In reality, your true anaerobic threshold might correspond more closely to your 35-, 45-, or 65-minute max power, depending on your physiology and fatigue profile.
In other words, FTP testing offers a useful approximation but doesn’t directly account for your individual power-duration curve or empirically pinpoint the physiological breakpoint where lactate accumulation accelerates. To do that, you'd need a formal lactate or ventilatory threshold test. While FTP gets you in the ballpark, we can get closer to the real picture. That’s where Critical Power (CP) testing comes in—it’s a more individualized, data-driven approach that offers deeper insight into your true metabolic profile.
What is Critical Power (CP)?
Critical Power (CP) represents the highest power output you can sustain while maintaining a physiological steady state. Below CP, key markers like blood lactate concentration, oxygen uptake, and hydrogen ion accumulation remain relatively stable. Above CP, these variables begin to rise rapidly, indicating a shift into a non-steady state where fatigue builds progressively. Once you're working above CP, you're operating on finite energy reserves and can only sustain that intensity for a limited duration.
The amount of work you can do above CP is called W′ (pronounced “W prime”). It reflects your anaerobic work capacity—the finite energy reservoir available for efforts exceeding CP. By performing multiple maximal efforts of different durations (commonly 3- and 12-minute tests), we can model your power-duration curve, calculate your CP, and quantify your W′.
This modeling approach was further refined through the work of Dr. Philip Skiba, who developed the W′ Balance Model—a tool that helps predict how W′ depletes and recovers during intermittent efforts. His research provides valuable insight into the dynamics of high-intensity performance and pacing.
Is critical power really better than FTP?
In practice, Critical Power (CP) is usually quite close to FTP—typically around 4–5% higher than an athlete’s 60-minute max power, based on our testing. While CP is generally considered a more precise and physiologically grounded metric, the difference between CP and FTP is often minimal for athletes with a typical power-duration curve. In those cases, using either metric to guide training and define intensity zones usually yields similar results.
That said, we always encourage athletes to think of CP, FTP, or their anaerobic threshold not as a single fixed number, but as a range of power. Physiological thresholds fluctuate slightly depending on fatigue, fueling, and environmental conditions, so treating threshold power as a flexible zone—rather than a rigid value—is a more accurate and productive approach to training.
However, for athletes with unusually high or low W′—or an atypical power curve influenced by factors like muscle fiber composition—the difference between calculated CP or FTP becomes more meaningful. These athletes may have disproportionately strong short-duration power or, conversely, excel in steady-state efforts with limited anaerobic contribution. In such cases, CP offers a clearer picture of their physiological capabilities and helps tailor training more effectively.
To capture these nuances, we perform multiple maximal efforts across different durations. This allows us to map how short-duration power outputs relate to longer ones, enabling a more individualized and accurate estimation of CP and W′—and ultimately, more effective training guidance.
How do you calculate CP?
The formula to calculate CP with two tests is:
((duration of longer test * avg power)-(duration of shorter test *average power))/(duration of longer test-duration of shorter test)
For example, if an athlete put out 350 watts for a 12-min test and 435 watts for a 3-min test, the formula would be:
((720 seconds * 350 watts)-(180 seconds * 435))/(720-180)= 322 watts. Meaning: the athlete’s CP is 322 watts.
Perhaps counterintuitively, if this athlete put out MORE power during the 3-min test, their CP would be LOWER, as it would represent a steeper decline from 3-min to 12-min power, and therefore the assumption would be that this relative decline would continue down the power curve to CP (you can confirm this directly with tests of varying duration). An athlete with a high 3-min vs. 12-min power output would have a higher W’, which may be useful for crits or any race that requires time spent above CP. It could also be the case that this athlete needs to develop “aerobically”/build endurance/enhance mitochondrial health and function (especially if they are a new athlete). Alternatively, if an athlete has a low 3-min vs. 12-min power output, it may be worthwhile focusing on developing higher-end fitness or tweaking high-intensity workouts to accommodate the athlete’s lower max power or W’.
What is the Deal with W’?
As mentioned above, W’ is the amount of energy (measured in kilojoules) you have to burn above CP before you’re toast. The athlete who put out 350 watts for a 12-min test and 435 watts for a 3-min test would have a W’of around 20, meaning they have 20 kilojoules (or 20,000 joules) before their battery is depleted. In this way, if you know your W’, you know exactly how hard you can go in training or racing before exhaustion. I talk about W’ more in-depth in this podcast where Miguel Mattox and I discuss the results of his CP test. Again, if you want to really dive in, check out the work done by Dr. Philip Skiba (linked further above), who did his Ph.D. on the concept.
Racing/Training Intensity Zones
Once you know your critical power, you can use it like you’ve used FTP. Because CP is typically slightly higher than FTP, feel free to drop each intensity zone by a percentage point or two. In reality, most people would be fine replacing it directly (especially if you’ve done shorter tests to establish your FTP, which we’ve found tend to overestimate 1-hour max power), but you need to confirm this in training. Especially in the race-specific training phase, you should dial in power targets by experimenting and confirming what your fitness allows you to do.
Race power targets as a percentage of Critical Power
If you’re a beginner or slower athlete, err toward the lower end of the range. If you’re elite, target the higher end:
Sprint Triathlon: 90-100%+ of CP
Olympic Distance Triathlon: 85-95% of CP
70.3 Triathlons: 75-90% of CP (mid-pack athletes should target around 80-83%)
Ironman Triathlons: 65-80% of CP (mid-pack athletes should target around 70-72%)
Conrad Goeringer is an Ironman Certified Coach based out of Nashville, TN. He is the founder of Working Triathlete and author of the book The Working Triathlete. His passion is helping athletes of all levels and with all schedules achieve their endurance goals. Reach out to learn more about Working Triathlete coaching packages and for a free consultation with a WT coach.