FTP Isn’t Everything: Understanding FRC, W’ and the Full Picture of Power Profiling

FTP Isn’t Everything: Understanding FRC, W’ and the Full Picture of Power Profiling

For years, FTP (Functional Threshold Power) has been treated as the golden metric in cycling. It’s a helpful anchor — the power you can sustain for about an hour — and it forms the basis for many training zones and plans. But as powerful as FTP is, it’s just one piece of the puzzle.

To truly understand an athlete’s capabilities — especially for racing, surging, sprinting, or repeated hard efforts — we need to look beyond FTP. That’s where FRC (Functional Reserve Capacity) and W’ (W prime) come in.

What Is FRC?

FRC, or Functional Reserve Capacity, is the amount of work you can do above FTP before you fatigue. Measured in kilojoules (kJ), it tells you how much “anaerobic battery” you’ve got to spend when you’re pushing beyond threshold — think breakaways, sprints out of corners, or surges over climbs.

FRC isn’t just for crit racers or sprinters. Even endurance-focused riders benefit from knowing their FRC. Why? Because many decisive race moments — especially in road races or fondos — happen above threshold.

Example:

Two riders have the same FTP of 280W.

• Rider A has an FRC of 18 kJ.

• Rider B has an FRC of 12 kJ.

In a series of short hills or surges above threshold, Rider A can repeatedly produce higher power for longer before fatiguing.

What Is W’?

W’ (pronounced “W prime”) is the same concept as FRC but used primarily in modeling by tools like GoldenCheetah or Xert. W’ also quantifies how much energy you can expend above your CP (Critical Power, another version of threshold).

Think of FRC/W’ like a battery:

Every time you ride above threshold, you’re draining it. Ride below threshold, and you’re recharging. Understanding how quickly you burn through it — and how long it takes to recharge — is crucial for pacing and planning efforts.

How to Find Your FRC / W’?

You can get your FRC in tools like WKO5, Intervals.icu, or TrainerRoad by looking at your Power Duration Curve. The software fits your curve and estimates how much anaerobic work capacity you’ve got based on your performance data over different time intervals (e.g., 30s, 1min, 2min efforts).

Want to see your real-world FRC? Do some testing:

• 30s all-out effort

• 1-min max effort

• 2-3 min hard efforts

  
  

  Then plug the data into WKO5 or Intervals.icu and look at how your curve stacks up.

How to Train FRC

To raise your FRC or W’, you need to stress that system — short, high-intensity work with incomplete recovery. Think:

• 30s–90s all-out intervals

• Tabata-style sessions (20s on / 10s off)

• Over/Unders that spend time just over threshold

But here’s the trick: you can’t do this kind of training all the time. It’s hard on the body and should be planned within a smart training block focused on anaerobic or race-specific development.

FTP, FRC, and the Big Picture

Rather than seeing FTP as the destination, think of it as one coordinate in a bigger performance map. FTP tells you what you can sustain. FRC/W’ tells you how hard you can surge — and how often — before you’re toast.

When you combine these with other metrics like VO2max, TTE (Time to Exhaustion), and sprint power, you start building a full performance profile. And that’s where coaching gets personal, precise, and powerful.

Wrap-Up

If you’re training with power and only looking at FTP, you’re leaving data — and performance — on the table. Learn your FRC. Understand your W’. And train like an athlete who sees the whole picture.

Want help building your full power profile and creating a training plan that hits your strengths and weaknesses? Get in touch and let’s work together.