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Whichever sport you pick, the tool multiplies a single threshold anchor by a fixed set of ratios. Cycling uses the seven-zone Coggan model on FTP: Z1 up to 55%, Z2 56 to 75, Z3 76 to 90, Z4 91 to 105, Z5 106 to 120, Z6 121 to 150 and Z7 151 to 250 percent. Heart rate uses Joe Friel's bands on lactate threshold heart rate, running from Z1 through Z5a, Z5b and Z5c. Running multiplies your threshold pace by ratios from 0.85 to 1.50.
The anchor is the only number that matters, so measuring it properly is the whole job. Cycling defaults to 250 W FTP; heart rate defaults to 170 bpm and offers an HR input type dropdown so you can supply either lactate threshold HR directly or your HR max, which the tool multiplies by 0.85 to derive LTHR. Running takes a threshold pace in mm:ss format, in either min/km or min/mi, and the pace table is inverted so faster paces are lower numbers.
Deriving LTHR as 85% of HR max is a population average that can be several beats off for an individual, so a directly measured threshold is always better. The tool has no field test built in — it will not estimate FTP from a 20-minute effort or a max heart rate from your age, so an inaccurate anchor propagates straight through every zone. The running ranges are described in the code as McMillan-style ratios rather than McMillan's own published tables, and no zone model here accounts for heat, altitude or fatigue.
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What if I only know my maximum heart rate? +
Choose Heart rate as the sport and set HR input type to HR max. The tool multiplies your entry by 0.85 to estimate lactate threshold heart rate and builds the Friel zones from that. It displays the derived LTHR so you can sanity-check it.
What are the Coggan power zone percentages of FTP? +
Active recovery up to 55%, endurance 56 to 75, tempo 76 to 90, threshold 91 to 105, VO2 max 106 to 120, anaerobic 121 to 150 and neuromuscular 151 to 250 percent. Entering your FTP converts every one of those into a watt range.
Why are there seven zones rather than five? +
Both the cycling and heart rate models here run to seven bands. Coggan adds anaerobic and neuromuscular zones above VO2 max, while Friel splits the top zone into Z5a, Z5b and Z5c to separate threshold work from aerobic capacity and anaerobic capacity.
How do I enter my threshold running pace? +
As minutes and seconds separated by a colon, such as 4:30, with the unit dropdown set to min/km or min/mi. Anything not matching that pattern is rejected and the zones stay blank. The output is returned in the same unit you selected.
What power should my easy endurance rides be? +
Zone 2 on the Coggan model, which is 56 to 75 percent of FTP. At the default 250 W FTP that is a 140 to 188 W range, described in the table as long aerobic base work. Zone 1 below it is easy spinning for recovery.