July 14, 2026 · 6 min read

FTP Isn't Everything — What Is FRC (Functional Reserve Capacity) and How to Train It?

FRC (Functional Reserve Capacity) is the total work in kilojoules you can do above FTP before you blow up. If FTP tells you how hard you ride "forever," FRC tells you how much you have "in the bank" for attacks, climbs and finishes above threshold. Typical values are 10–30 kJ — a sprinter has a large FRC and average FTP, a climber the opposite. They're two independent dimensions of fitness, trained differently.

FRC (in the WKO model) is the practical equivalent of W' (anaerobic work capacity). Picture a battery: FTP is the voltage you hold without draining, and FRC is that battery's capacity above threshold. Every second above FTP discharges it, every second below recharges it. When FRC hits zero, power drops sharply and you have to ease off. That's why two riders with an identical 280 W FTP can finish a race completely differently — FRC decides it.

How FRC differs from FTP

• FTP — steady power for ~40–60 min, aerobic capacity. Sets your pace in a time trial and on a long climb.
• FRC — a one-off "pool" of work above FTP, anaerobic capacity. Sets how many attacks you survive and how strong your finish is.
• Units — FTP in watts, FRC in kilojoules. You can have a high FTP and low FRC (time-trialist type) or the reverse (sprinter type).

What is FRC in simple terms?

FRC is your "fuel tank" for efforts above FTP — a reserve measured in kilojoules that you burn during an attack or sprint and rebuild by riding below threshold. The bigger your FRC, the more hard, above-threshold moves you make before power collapses. You can see it directly on your power curve in the window from a few seconds to a few minutes.

How to measure your FRC

Analytics platforms estimate FRC (by modeling W') from your power curve — they need good, maximal efforts at various durations. For the model to be accurate, supply data:

• Maximal 1 min effort — opens the top of the curve.
• Maximal 3–5 min effort — bridges the VO2max and anaerobic zones.
• A fresh FTP — without an accurate threshold, FRC computes wrong; run a Ramp Test first.

What's a typical FRC for an amateur?

For amateurs FRC usually sits in the 10–30 kJ range, with clearly sprinter-type profiles exceeding 30 kJ. The absolute value matters less than its change over time — a rising FRC at a steady FTP means you're building the "spark" above threshold, even if the threshold itself is flat.

How to train FRC

You build FRC with short, very intense efforts with full or near-full recovery — it's about quality, not volume:

• Depletion intervals — 5–8×1 min @ 130–150% FTP with full 3–4 min recovery. They teach the body to dig deeper into the reserve.
• Repeatability — micro-intervals 30/15 teach faster FRC rebuild between moves, key in a race.
• Sprints — 6–10×10–15 s maximal with long recovery, developing the top of the curve and anaerobic power.
• VO2max base — 4×8 and 5×5 intervals improve FRC recharge, because faster clearance supports reserve recovery.

Summary

FTP tells you how fast you ride at a steady pace, but FRC decides the attack, the climb and the finish. Treat it as a second, independent dimension of fitness: a kilojoule reserve of work above threshold, typically 10–30 kJ, built with short maximal efforts and micro-interval repeatability. Don't judge progress by FTP alone — also watch the top of your power curve and the FRC trend. Two riders with the same FTP are not the same rider if one has twice the reserve.

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