Functional Threshold Power (FTP)

In endurance sports, functional threshold is a practical benchmark near the boundary between steady and increasingly fatiguing work. It is widely used to set training zones, estimate training load, and track whether threshold-level performance is improving.

Two common terms are FTP for cycling and rFTP for running.

Functional Threshold Power (FTP)

FTP usually refers to cycling threshold power. It is commonly described as the highest average power you can sustain for roughly 60 minutes, though in practice it is an estimate that depends on testing method, pacing, fatigue, and recent training.

Why it matters

• Physiological anchor: FTP roughly aligns with the threshold range around Lactate Threshold (LT). Below it, many athletes can work for much longer; above it, fatigue accumulates faster.
• Relative-intensity reference: whether your FTP is 400 W or 150 W, percentages of FTP make workouts more comparable within an athlete’s own fitness context. Most power-based training plans use FTP percentages (for example, Zone 2 ≈ 55–75% FTP).

How to estimate FTP

1. 20-minute test (classic): ride all-out for 20 minutes, then take 95% of the average power.
2. Ramp test: increase load each minute to exhaustion, then use ~75% of the final minute’s power.
3. CP model estimate: Trainingload.ai can estimate from your Power Duration Curve (PDC), often using FTP ≈ 0.95 * CP.

If you want a file-based estimate, use the estimate FTP training load from an activity file. If you already have maximal efforts across durations, use the fit Critical Power and W' for training load planning to fit CP and W'.

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Running Functional Threshold Power (rFTP)

Running Functional Threshold Power (rFTP) became popular with the rise of running power meters (Stryd, Garmin, COROS, etc.).

It is commonly defined as the highest average running power you can sustain for roughly 60 minutes.

rFTP vs. FTP

Even though the definitions are similar, the numbers are usually not interchangeable:

• Different magnitude: many athletes have higher rFTP than cycling FTP. Running includes elastic energy storage/release (spring-like behavior), recruits more muscle groups, and typically yields higher heart rates.
• Test separately: don’t use cycling FTP to guide running training, and vice versa.

rFTP vs. threshold pace

• rFTP (power): measured in watts. Less affected by hills and wind (depending on the device/model), and often closer to physiological output.
• Threshold pace: measured in min/km. Strongly affected by terrain (pace slows uphill even when intensity is high).
  • Note: on flat, calm terrain, the pace corresponding to rFTP approximates threshold pace. On rolling trails, rFTP can be more stable.

How to estimate rFTP

Common running power tests (e.g. Stryd protocols):

• 3/9 test: 3 minutes all-out (then 30 minutes recovery) + 9 minutes all-out.
• CP model: fit Critical Power from maximal efforts of different durations (e.g. 30s, 2min, 10min); CP is often used directly as rFTP.

How Trainingload.ai uses FTP

Trainingload.ai uses FTP as a threshold reference for power zones, Intensity Factor, and Training Stress Score. If FTP is too low, hard workouts can look more stressful than they really were; if FTP is too high, training load and zone targets can be understated.

For plan review, FTP is most useful when it answers:

• Did the completed workout match the intended zone?
• Are TSS and IF being calculated from a current threshold?
• Has threshold fitness changed enough to update future workouts?

Summary

Trainingload.ai advice: Update your threshold settings regularly (every 4–8 weeks) so TSS calculations and training zones stay useful.

Related tools and docs

• Estimate FTP training load from an activity file
• Calculate Critical Power and W' for training load planning
• Power Zones
• Critical Power (CP)