Five zones on the bike computer, seven in a running app, three on a coach’s chart. The labels differ, but the problem is the same everywhere: wrong thresholds make every zone wrong.
Zones tell you which effort level you are in — as percentages of your swim, bike, and run thresholds. In triathlon those thresholds are CSS (Critical Swim Speed), FTP (Functional Threshold Power), and FT (Functional Threshold pace). Set them on Threshold Testing — protocols are in how to test — or sync from a clean race in the Race Vault.
WattX uses one five-zone model (Z1–Z5) across all three sports so you are not converting between apps in your head. Zones say how hard. Workout intensity says what the session is for, from recovery to speed. The Session Generator combines both — structured warm-up, work, and recovery with targets in min/100m (swim), watts (bike), or min/km (run). With a WattX Race Plan PRO, your Plan Page feeds the same structure day by day: right intensity, right zone, right work/recovery durations.
Knowing the label for Z3 does not tell you whether today’s set belongs there — that comes from honest thresholds and a session with one clear job. When I ran weekly track sessions at the club, “tempo” meant different paces to different people until we agreed on the numbers underneath.
Physiology
What Zones Actually Are
At low intensity you rely on aerobic metabolism — fat oxidation, efficient lactate clearance. As intensity rises you cross aerobic threshold (Z2/Z3 boundary) then lactate threshold (Z3/Z4 boundary), then approach VO₂ max (maximal oxygen uptake — Z5).
Train in the wrong zone and you either don’t stress your body enough, or you pile up fatigue without getting the adaptation you wanted.
Zones come from CSS, FTP, and FT in your profile. Update on Threshold Testing or from a clean race in the Race Vault — the Session Generator and plan feed sessions with the right zone targets, work/recovery structure, and watts or pace automatically.
Overview
WattX Five-Zone Overview
The critical boundaries are Z2↔Z3 (aerobic threshold) and Z3↔Z4 (lactate threshold).
Swim zones
Swim, Bike, and Run Zones
- Z1>130%
- Z2110–130%
- Z3103–110%
- Z497–103%
- Z5<95%
Example: with a CSS of 1:45/100m, Z2 is 1:56–2:17/100m. Use Z5 in short sets only.
- Z1<55%
- Z256–75%
- Z376–90%
- Z491–105%
- Z5106%+
Long-course training is mostly Z1–Z2; sprint training swaps some of that base for Z4–Z5.
- Z1>115%
- Z2106–115%
- Z3101–105%
- Z495–100%
- Z5<90%
Example FT 5:00/km → Z4 is 4:45–5:00/km. Use RPE on hills.
High-intensity swim volume is limited by technique breakdown — Z5 appears in shorter sets, not endless repeats. How much time you spend in each zone depends on distance, phase, and session type. See race planning for how phases change the balance.
Honest thresholds
Wrong Thresholds, Wrong Training
Z2 feels like Z3; threshold work becomes VO₂ and you stall. Every “endurance” ride turns into tempo.
Hard sessions never reach the intensity they are meant to, so you arrive at race day under-prepared for race pace.
Retest on Threshold Testing — or see how to test — so Z1–Z5 stay honest.
For race day, see Race Pacing Targets. For long-course fuelling, see the nutrition guide.