How this calculator works
Heart rate reserve is the gap between maximum and resting heart rate. Each zone is a percentage of that reserve added back to the resting rate, which is the Karvonen method. Five zones cover recovery, aerobic endurance, tempo, threshold and VO2 max. In a triathlon, the same zone feels different in each sport: swimming heart rate is often lower at a given effort because the body is horizontal and the water cools it, while cycling and running track more closely with land-based zones. The table gives the beats per minute for each zone and a typical triathlon use.
Formula
Heart rate reserve = maximum heart rate - resting heart rate. Zone lower bpm = resting + reserve x lower share. Zone upper bpm = resting + reserve x upper share. Shares are 50 to 60 percent for zone 1, 60 to 70 for zone 2, 70 to 80 for zone 3, 80 to 90 for zone 4 and 90 to 100 for zone 5.
Worked example
A maximum of 185 and a resting rate of 60 give a reserve of 125. Zone 2 runs from 60 + 125 x 0.60 = 135 bpm to 60 + 125 x 0.70 = 147.5 bpm. Zone 4 runs from 60 + 125 x 0.80 = 160 bpm to 60 + 125 x 0.90 = 172.5 bpm. Zone 5 reaches the maximum at 185 bpm.
Advertisement
Frequently asked questions
Should I use heart rate or pace and power?
Heart rate lags behind effort, especially at the start of a race, and is affected by heat, caffeine and fatigue. Power on the bike and pace in the pool and on the run are more immediate. Heart rate is still useful as a check on overall stress and recovery.
Why is my swim heart rate lower than my run heart rate?
In the water the body is horizontal and cooled by water, and the pressure changes how blood returns to the heart. Most swimmers see a lower maximum in the pool, so pool zones should be set from a pool test rather than a treadmill test.
How do I find my true maximum heart rate?
A supervised field test or a hard race is better than an age formula. Warm up thoroughly, run several minutes hard up a hill, then sprint to the top. Repeat after recovery and take the highest reliable reading. Stop if you feel unwell.
Do the zones change with fitness?
Resting heart rate usually falls as fitness improves, and maximum heart rate may stay the same or drift down slightly with age. Recheck resting rate every few weeks and update the table when it changes.