Heart rate zones for triathlon: practical guide

Why 220 – age isn't enough

The 220 – age formula gives a theoretical max HR. The problem? For two triathletes of the same age, real-world difference can hit 30 bpm. Training at 75% of a wrong max HR means missing your zone every time.

The only serious way to set zones is a per-discipline field test: a 20-minute max effort for HR threshold, or an FTP test on the bike. Once threshold is known, zones are calculated as a percentage of that threshold, not max HR.

The 5 zones and what they're for

The 5 HR zones map to 5 distinct physiological intensities. Each drives a different adaptation: aerobic endurance, economy, aerobic capacity, threshold, VO2 max. Mixing zones means missing the targeted adaptation.

• Z1 (50-60% threshold): Active recovery, day after hard sessions
• Z2 (60-75% threshold): Aerobic endurance, 70-80% of total volume
• Z3 (75-85% threshold): Tempo, gray zone, use sparingly
• Z4 (85-95% threshold): Threshold, intensity of half-marathon and 10K bike
• Z5 (95-105%+ threshold): VO2 max, short reps 30 sec to 5 min

Zones change by discipline

Classic mistake: applying running zones to the bike. Your cycling threshold HR is typically 5 to 10 bpm below running threshold, and lower still in swimming (position, hydrostatic pressure).

Concretely: one 20-min test per discipline. The output is three HR zone sets used in parallel. A triathlon watch manages them automatically.

HR or power?

On the bike, power (FTP) is more precise than HR, which drifts with heat and fatigue. In running, pace or running power take over. HR remains an excellent guardrail in endurance and a unique tool in swimming where power isn't accessible.

TriCoach AI prescribes every session with HR AND power/pace, and lets you pick your primary metric based on the gear you actually own.