Threshold is Not a Number: Why FTP Fluctuates More Than You Think

You are not defined by your FTP!

Threshold Is Not a Number

For years, FTP (Functional Threshold Power) has been sold as a fixed metric — the single number that defines your cycling ability. It’s used to set zones, plan intervals, and compare riders. But here’s the truth: FTP is not fixed. It fluctuates — daily, weekly, seasonally.

So if you’ve been frustrated because your “FTP feels off,” or your legs don’t match the numbers on screen… you’re not alone. And you’re not wrong.

What FTP Really Measures

Let’s start here: FTP is a modelled estimate of the power you can sustain at lactate steady state, often defined as ~60 minutes of max sustainable output. It’s a useful benchmark — but not absolute.

Your actual threshold varies based on:

• Training load and accumulated fatigue

• Nutrition and fueling (especially carb availability)

• Sleep and recovery quality

• Time of day and testing method

• Environmental factors (heat, altitude, even hydration)

One week it might be 305W. Another? 290W. The number itself is just a snapshot — the context around it matters more.

Testing vs. Reality

FTP tests — whether a 20-minute test, ramp test, or modeled FTP from WKO5 — are estimates.

They’re useful for benchmarking trends, but they don’t always reflect how strong you feel on the day or what you can do in a race scenario.

That’s where fatigue resistance, Time to Exhaustion (TTE), and work capacity above threshold (like FRC or W’) start to matter more.

Why It Matters for Your Training

Treating FTP as gospel can cause a few problems:

• You might over- or under-train, depending on how accurate your current number is.

• You could get discouraged if you don’t hit prescribed intervals, even though you’re progressing.

• You might ignore more powerful metrics like TTE, Stamina, and short-duration power, which paint a clearer performance picture.

Instead of obsessing over hitting an FTP test result, try this:

• Use FTP to set ballpark training zones, but listen to your body.

• Track trends over time, not just individual tests.

How I Approach It with My Athletes

I use FTP as a starting point — never an endpoint. We adjust zones if needed, based on:

• Recent race performance

• Daily readiness and recovery (sleep, HRV, RHR)

• Subjective effort and ride feel

• Power curve changes over time

I also encourage riders to fuel for the work required — low-carb endurance rides are fine, but if you’re doing threshold or VO2max efforts, you need carbs in the tank or you’ll underperform. That affects how “accurate” your FTP feels, too.

Bottom Line: Threshold Is a System, Not a Single Number

Your threshold is always adapting. It’s not static, and that’s a good thing — it means your body is responding to training, recovery, and life. Don’t chase a perfect FTP number. Build your performance ecosystem instead.

Want a smarter way to train?

Book a free consult and I’ll show you how to build a power profile that goes way beyond FTP.

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