Triathlon Heart Rate Training Zones Calculator

The Karvonen formula calculates target heart rates using your Heart Rate Reserve (HRR), which is your maximum heart rate minus your resting heart rate. The formula for a zone boundary at a given percentage is: Target HR = Resting HR + (% x HRR). Because HRR reflects individual fitness, two athletes with the same maximum heart rate but different resting rates will get different zone boundaries. For triathlon, where athletes range from beginners with resting HRs above 70 bpm to highly trained athletes below 40 bpm, using HRR gives meaningfully more personalised zones than simple max-HR percentage methods.

Cycling produces a lower heart rate than running at the same perceived effort, primarily because your body weight is supported by the saddle, reducing the cardiovascular cost of forward movement. Most coaches apply a sport-specific offset of around 5 bpm for cycling relative to running. Swimming uses an even larger offset of around 10 bpm due to the horizontal body position (which assists venous return to the heart), cooler water (which slows the heart slightly), and the lower muscle mass of most swimmers compared to runners. If you have tested your maximum heart rate in each sport, you can enter those tested values directly for the most accurate zones.

Measure your resting heart rate first thing in the morning before getting out of bed, sitting up, or reaching for your phone. A wrist or chest-strap heart rate monitor gives the most accurate reading. Take the measurement over three to five consecutive days and use the average. Resting HR for untrained adults is typically 60-80 bpm; well-trained endurance athletes often measure 40-55 bpm; elite triathletes may be below 40 bpm.

A widely supported guideline for triathlon is the 80/20 rule: approximately 80% of your weekly training volume (by time or distance) should be in Zones 1 and 2, with the remaining 20% in Zones 4 and 5. Zone 3 should be kept to a minimum (under 10-15% of volume) because it is fatiguing without delivering the aerobic base benefits of Zone 2 or the high-intensity adaptations of Zones 4 and 5. Zone 1 is appropriate for warm-ups, cool-downs, and active recovery between hard efforts. Zone 5 intervals are short (30 seconds to 3 minutes) and used only when peak VO2 max development is the goal, typically in the last 6-8 weeks before a sprint or Olympic-distance race.

No. Heart rate responds differently across swimming, cycling, and running, so each discipline should have its own zone set. This calculator applies the standard offsets (cycling minus 5 bpm, swimming minus 10 bpm relative to running) to your base max HR before computing zones. If you have individually tested your max HR in each sport, enter those values separately for each discipline to get the most accurate result. Using running zones for a swim session will likely have you working harder than intended, which accumulates unnecessary fatigue.

Cardiac drift is the gradual rise in heart rate that occurs during prolonged steady-state exercise even when pace or power stays constant, caused by dehydration, heat stress, and muscle fatigue. On long training sessions of two or more hours, your heart rate may drift 5-15 bpm above your intended zone without any change in effort. To account for this, many coaches recommend using perceived exertion or pace/power as the primary guide on very long sessions, treating heart rate as a secondary check rather than the sole determinant of zone compliance.