About

Generic heart rate zones are insufficient for competitive athletes. This advanced tool implements the Joe Friel 7-Zone system, the gold standard for cycling and triathlon training. Unlike simple Max HR percentages, this system anchors zones to the Lactate Threshold Heart Rate (LTHR) - the precise intensity where lactate accumulation begins to exceed clearance. This accounts for individual metabolic variance that Max HR formulas ignore. The tool also supports the Karvonen (Heart Rate Reserve) method for those prioritizing cardiovascular range over metabolic breakpoints.

Formulas

The Joe Friel Method calculates zones relative to LTHR:

ZoneHigh = LTHR × Factor

The Karvonen Method utilizes resting heart rate:

Target = ((Max - Rest) × %) + Rest

Reference Data

Friel Zone	Name	% of LTHR	Physiological Adaptation
1	Recovery	< 81%	Active recovery
2	Aerobic	81% - 89%	Mitochondrial enzymes, capillaries
3	Tempo	90% - 93%	Glycogen storage, muscle endurance
4	SubThreshold	94% - 99%	Raise lactate threshold
5a	SuperThreshold	100% - 102%	Acidosis tolerance
5b	Aerobic Cap	103% - 106%	VO2 Max
5c	Anaerobic	> 106%	Neuromuscular power

Frequently Asked Questions

Perform a 30-minute time trial at the maximum sustainable pace. Your average heart rate for the *last 20 minutes* of this effort is a close approximation of your LTHR.

The standard Zone 4 and 5 are too broad for elite training. Friel splits high intensity into SubThreshold (sweet spot), SuperThreshold (time trial pace), and Aerobic Capacity (VO2 Max intervals) to target specific energy systems.

The Friel LTHR method. Cycling is highly dependent on functional threshold power (FTP), which correlates strongly with LTHR. Max HR is less relevant for pacing time trials.