Is FTP “Dead”? What Critical Power Research Reveals

Is FTP “Dead”? What Critical Power Research Actually Reveals

If you train with power, one number quietly runs your entire season: Functional Threshold Power, or FTP. It sets your Zwift zones, your TrainingPeaks targets, and the pacing plan you carry into your next 70.3 bike leg. Over the past year or so, a genuinely interesting debate has spread from physiology podcasts into r/triathlon and the TrainerRoad forums: is FTP actually a flawed, oversimplified number, and should age-group athletes be paying attention to a different metric — Critical Power (CP), paired with a companion value called W’ (“W-prime”) — instead?

The honest answer sits between the hype and the backlash. FTP is not “dead,” and you don’t need to throw out your current zones. But the physiological critique of FTP is well-supported by research, and understanding what Critical Power actually measures can make you a smarter, more realistic pacer on race day — particularly on the bike leg, where blowing your matches early is one of the most common ways age-groupers wreck their run.

Where FTP Came From, and Why It Became the Default

FTP was popularized as a training-zone shortcut, not as a term from exercise physiology textbooks. In practice, it’s usually estimated from a 20-minute maximal time trial (take the average power, multiply by roughly 0.95) or an 8-minute maximal effort (multiply by roughly 0.90). Both protocols are fast, repeatable, and don’t require a lab — which is exactly why every major platform, from Zwift to Garmin Connect to TrainingPeaks, adopted some version of it as the default zone-setting metric.

The problem, according to sport-science reviewers, is that this convenience comes at a cost of precision. A comprehensive narrative review by Chorley and Lamb describes FTP as “de facto arbitrarily defined” — a one-hour power estimate backed into from a much shorter test, using a fixed percentage that was chosen for convenience rather than derived from an individual athlete’s physiology.

That same review found FTP correlates strongly, at a group level, with other recognized endurance markers — lactate threshold, maximal lactate steady state (MLSS), and Critical Power. Strong correlation across a population sounds reassuring, but it hides a more important detail: several of the underlying studies found FTP significantly over- or under-estimates an individual’s true physiological threshold depending on the exact protocol used, and the individual limits of agreement were large even when the group-level correlation looked tight. In plain terms: FTP might describe “athletes in general” reasonably well while still being noticeably wrong for you, specifically.

What Critical Power Actually Measures

Critical Power comes from a different, older, and more rigorously defined tradition in exercise physiology: the two-parameter power-duration relationship. Instead of estimating a single number from one test, CP modeling uses several maximal efforts of different durations to map how sustainable power output declines as effort duration increases. According to the Chorley and Lamb review, this marks a genuine physiological boundary between the “heavy” and “severe” exercise intensity domains — below CP, the body can approach a metabolic steady state; above it, fatigue accumulates on a clock that never stops running.

The companion value, W’, represents a finite reserve of work capacity available above Critical Power — sometimes described informally as your “matches.” Every surge, hill, or hard bridge effort above CP burns through this reserve, and once it’s gone, power output drops sharply no matter how much you want to keep pushing. This is directly relevant to triathlon pacing: a hard attack up a hill in the first 20km of an Ironman bike leg can spend matches you needed for the final climb — or for the run.

So Is FTP “Dead”? What the Evidence Actually Supports

The physiological critique of FTP is well-evidenced by the Chorley and Lamb narrative review: it is a useful, practical proxy, not a precise measurement of any single underlying physiological threshold. It correlates reasonably well with lactate threshold, MLSS, and CP at a group level, but is not statistically interchangeable with any of them for a given individual, and the exact protocol used to estimate it (20-minute vs 8-minute test) changes the answer.

Where the evidence gets more mixed is on whether Critical Power is a practically better everyday training tool for the average age-group triathlete. CP is conceptually superior — it’s grounded in an established model with a real physiological boundary, and CP plus W’ together let you estimate how long you can sustain an effort above threshold, which is directly useful for pacing race-day surges. But testing it properly is a burden: traditional CP protocols require multiple exhausting, maximal time-trial-style sessions on separate days, which is a lot to ask of a time-crunched athlete already balancing swim, bike, run, and life.

Newer single-session alternatives — the 3-minute all-out test and the ramp all-out test — trade some of that burden away, but they do so at the cost of some precision, and W’ reconstitution (how quickly you recover “matches” burned above threshold during a race) varies substantially between individuals and remains an active area of research rather than a fully solved problem. In short: the case against treating FTP as a precise physiological number is strong; the case for CP/W’ as a clearly superior everyday tool for most age-groupers is real but still developing, and depends on how much testing burden you’re willing to accept.

This debate has moved well beyond academic journals — it’s been argued out on physiology-focused shows like Fast Talk Laboratories, and in long-running threads on r/triathlon and the TrainerRoad forum, where age-groupers compare their own testing experiences and question whether their zones actually reflect their physiology.

Why This Matters Specifically for Triathletes

Pure cyclists can afford to think about FTP and CP purely in terms of bike performance. Triathletes can’t — every watt spent above threshold on the bike has a downstream cost on the run. This is exactly why the CP/W’ framing is so relevant to age-groupers, even if you never run a formal CP test: the practical question isn’t just “how much power can I hold,” it’s “how much of my limited above-threshold reserve am I willing to spend before I still need to run a half or full marathon off the bike.” Framing pacing this way — as a finite budget rather than a simple ceiling — is a more physiologically honest mental model than treating FTP as a single hard line you either stay under or don’t.

Consider two athletes with an identical FTP of 250W racing a hilly half-Ironman. One rides every climb steadily at 90% of FTP and holds a smooth, even effort. The other repeatedly surges to 320–350W on the same climbs to hold contact with a group, then eases off on the descents to “recover.” Their average power for the ride might look similar, and both might report they “stayed close to FTP” — but the second athlete has spent considerably more of their W’ reserve on repeated above-threshold surges, and Critical Power research suggests that reserve doesn’t come back quickly during easy descents. That is very often the athlete who reports “dead legs” in the opening kilometers of the run, even though their bike power data looks unremarkable on average.

Practical Application: Using FTP and CP Without Overcomplicating Your Training

You don’t need to abandon FTP-based zones to benefit from this research — you need to use FTP with appropriate humility about what it can and can’t tell you. A few practical adjustments:

• Treat your FTP number as a training-zone anchor, not a race-day contract. Because individual limits of agreement between FTP and true threshold can be large, don’t assume your 20-minute-test-derived number perfectly predicts what you can sustain for 90–180 minutes on race day.
• If you want more insight into your durability above threshold, consider a Critical Power estimate using two or three maximal efforts of different durations (for example 3–5 minutes and 12–20 minutes) rather than relying purely on a single 20-minute test. This starts to approximate the CP/W’ relationship without requiring a full laboratory protocol.
• Think in terms of “matches” on race day. Every effort meaningfully above your threshold power — a hill surge, a bridge to a group, fighting a headwind out of the saddle — spends part of a finite reserve. Long-course athletes in particular should treat early-race surges as a withdrawal from a limited account, not a free action.
• Retest sparingly and consistently. Retesting FTP every couple of weeks chasing a bigger number turns a training-zone tool into a source of anxiety and can distort session pacing around “beating last time” rather than building fitness.

A Note on Safety Before Any Maximal Test

Both FTP tests (20-minute or 8-minute all-out efforts) and Critical Power protocols (multiple maximal time trials, 3-minute all-out tests, or ramp tests) are, by design, maximal or near-maximal cardiovascular efforts. They carry the same exertion risks as any all-out exercise test. Athletes should be medically cleared for vigorous exercise, warm up properly beforehand, and stop immediately if they experience chest pain, unusual breathlessness, dizziness, or other concerning symptoms. Anyone with cardiac risk factors, a relevant family history, or who is new to structured training should consult a physician before attempting a maximal power test, and should not treat online testing protocols as a substitute for medical judgment.

Common Mistakes Age-Groupers Make With FTP and CP

• Chasing a bigger FTP number as a goal in itself, rather than as a byproduct of well-structured training — this can push athletes toward retesting too frequently and skewing intensity distribution toward too much threshold-adjacent work.
• Assuming a single 20-minute indoor test number applies identically to long-course race pacing 90+ minutes on the bike, ignoring that fatigue resistance and durability over several hours are a different physiological question than a 20-minute maximal effort.
• Ignoring pacing above threshold entirely because “I stayed under my FTP average,” when in reality repeated short surges above threshold can still burn meaningful W’ reserve even if the overall average power looks conservative.
• Attempting a maximal CP or FTP test without adequate warm-up, hydration, or a recent health check — particularly relevant for returning athletes or those with any cardiovascular risk factors.
• Overhauling training zones dramatically based on one new test result, rather than treating any single test as one data point in a longer trend.

How to Apply This Week

• Review how your FTP number was actually generated — 20-minute test, 8-minute test, ramp test, or platform estimate — and treat any number derived from a single short test as an approximation rather than a fixed truth.
• In your next hard group ride or key workout, notice how many “surges” above threshold you make and how you feel afterward — this builds intuition for your own W’ reserve without needing formal lab testing.
• If you have access to recent maximal efforts of two different durations (for example a recent 5-minute max and a recent 20-minute max), you can start to see how your own power-duration curve behaves, which is more informative than a single FTP number alone.
• Before your next race, plan where you are and are not willing to spend matches — identify the one or two hills or moves worth a deliberate surge, and commit to riding the rest closer to a sustainable, threshold-respecting pace.
• If you’re planning any maximal test, book it when you’re rested, properly warmed up, and — if you have any cardiovascular risk factors or are new to structured training — after checking in with a physician.

Closing Summary

FTP isn’t dead, but it also isn’t the precise physiological truth many training platforms imply it is. The research is clear that FTP is a convenient, imperfect proxy for underlying thresholds like lactate threshold and Critical Power — useful for setting practical training zones, but not something to treat as gospel or chase upward as an end in itself. Critical Power and W’ offer a more physiologically grounded way to think about pacing, especially for the surges and hills that define real race-day bike legs, but the practical testing burden means most age-groupers will get more value from applying CP concepts qualitatively — thinking in terms of a limited “match” reserve — than from chasing a perfectly precise CP number. Keep your FTP-based zones, hold them loosely, and always put safety first around any maximal effort.

References

• Chorley and Lamb, “The Application of Critical Power, the Work Capacity above Critical Power, and its Reconstitution: A Narrative Review,” Sports (MDPI), 2020 — PMC/NIH
• “Is FTP Dead? Exploring the Relevance of Functional Threshold Power in Modern Training” — Fast Talk Laboratories (YouTube)
• “Is FTP Dead? Is Critical Power the Cyclist’s Next Great Training Metric?” (YouTube)
• “Are FTP Tests Pointless?” — Tri To Disagree! (YouTube)
• Cycling FTP discussion — r/triathlon (Reddit)
• The Triathlon/Ironman Training Thread 2025 — TrainerRoad Forum