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.

What is the Triathlon Multi-Sport Training Zones?

Input your swim CSS pace, bike FTP, and running threshold pace to generate aligned 5-zone training ranges across all three triathlon disciplines, using the percentage models that coaches apply for pace and power. It runs free in your browser on Gera Tools, with nothing uploaded.

Triathlon Multi-Sport Training Zones

Name: Triathlon Multi-Sport Training Zones
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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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.

Worked example

With a CSS of 1:40/100 m, an FTP of 250 W, and a run threshold of 4:30/km:

Zone	Bike (watts)	Swim (per 100 m)	Run (per km)
Z1 Recovery	below 140	slower than 2:05	slower than 5:21
Z2 Endurance	140–188	1:46–2:05	4:47–5:21
Z3 Tempo	188–213	1:43–1:46	4:38–4:47
Z4 Threshold	213–238	1:40–1:43	4:30–4:38
Z5 VO2	238+	faster than 1:40	faster than 4:30

Illustrative only — your numbers will differ.

How to find your thresholds

Swim CSS (Critical Swim Speed): swim a time-trial 400 m, rest, then swim a time-trial 200 m. CSS per 100 m = (400 m distance − 200 m distance) ÷ (400 m time − 200 m time) × 100, converted to a per-100 m pace.

Cycling FTP: the gold standard is a 60-minute maximal effort. A commonly used shortcut is a 20-minute test, taking 95% of average power as an FTP estimate. An hour is a tough effort to properly pace, so a structured ramp test is another valid approach.

Run threshold pace: run at the fastest pace you could hold for a one-hour race. An accurate approach is a 30-minute time trial at maximum effort; the average pace is a close proxy for threshold.

Zone training in practice

Zone 1 and 2 (recovery and endurance) should account for about 75–85% of weekly training volume in a polarised approach. These sessions build aerobic base without accumulating fatigue.
Zone 3 (tempo) sits in an awkward middle ground — hard enough to be tiring but not hard enough to drive the adaptations that zones 4 and 5 produce. Most coaches use it sparingly.
Zone 4 (threshold) is the most important zone for improving race pace, particularly over Olympic and sprint distances. Intervals here drive lactate tolerance.
Zone 5 (VO2 and above) builds peak aerobic capacity. Short, intense swim, bike, or run intervals typically 2–5 minutes long.

Retest thresholds every 4–8 weeks of focused training, or when easy paces start feeling too easy. Stale anchors leave you under-training as fitness improves.