What are CSS, FTP, and threshold pace?

CSS, or Critical Swim Speed, is the swim pace you can hold for a long sustained effort, found from a 400 m and 200 m test. FTP is the cycling power you can hold for about an hour. Run threshold pace is the running pace at your lactate threshold, near a one-hour race effort. All three anchor zone calculations for their sport.

Why do bike zones use power but run and swim use pace?

Cycling power meters measure output directly, so FTP percentages are the standard. Swimming and running rely on pace because power is harder to measure there. The 5-zone structure is shared, but each sport scales it from its own threshold anchor.

How do the zone percentages work?

For power, zones are percentages of FTP, for example Zone 2 endurance is 56 to 75 percent of FTP. For pace, slower than threshold means a larger time per distance, so endurance pace is found by dividing threshold pace by a fraction below one, which lengthens the time appropriately.

Should I retest my thresholds often?

Retest every four to eight weeks of focused training, or whenever your easy paces start to feel too easy. As fitness improves, thresholds rise and zones shift faster, so stale numbers lead to training that is too gentle to drive adaptation.

Are these zones the same as heart-rate zones?

No. These are pace and power zones, which respond instantly and are not affected by heat, fatigue, or caffeine the way heart rate is. Many triathletes use pace and power for the prescription and heart rate as a secondary check on internal load.

Triathlon Multi-Sport Training Zones

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This calculator builds a consistent 5-zone training framework across all three triathlon disciplines from a single set of threshold tests: swim CSS pace, cycling FTP, and running threshold pace. Aligning the zones lets you prescribe the same intensity language — recovery, endurance, tempo, threshold, VO2 — in the pool, on the bike, and on the run.

How it works

Cycling zones are percentages of FTP power. Pace zones are trickier because a slower pace means a larger time per distance, so easier zones divide threshold pace by a fraction below one:

Power Z2 endurance = FTP × 0.56 … 0.75
Pace  Z2 endurance = threshold pace ÷ 0.84 … 0.94   (slower = bigger time)
Pace  Z5 VO2       = threshold pace ÷ 1.03 … 1.06   (faster = smaller time)

The five zones used are recovery (Z1), endurance (Z2), tempo (Z3), threshold (Z4), and VO2/anaerobic (Z5), following the Coggan-style power model and common CSS/run-pace percentage bands.

Example and tips

With a CSS of 1:40/100 m, an FTP of 250 W, and a run threshold of 4:30/km, your bike endurance zone is roughly 140–188 W, your swim endurance pace is around 1:46–1:59/100 m, and your run endurance pace is about 4:47–5:21/km. Keep easy days genuinely easy — most athletes ride and run their Zone 2 work too hard. Retest every four to eight weeks, because as your thresholds rise the whole zone structure shifts and stale anchors leave you under-training.