Lactate Threshold Heart Rate (LTHR) represents the highest heart rate you can sustain for a prolonged period without lactate building up too quickly in your blood.
It marks the point where your body shifts from aerobic to anaerobic effort, and where fatigue begins to accumulate more rapidly.
In training, LTHR is one of the most useful performance markers for setting heart rate training zones.
By training just below or around your LTHR, you can improve endurance, increase efficiency, and delay fatigue during sustained efforts.
Unlike maximum heart rate (HRmax), which is largely genetic, your LTHR can improve with consistent fitness training.
It adapts over time as your aerobic capacity and lactate clearance improve.
You can determine your LTHR through field tests — such as a 30-minute time trial where you record your average heart rate — or estimate it from data collected during hard workouts or races.
Knowing your LTHR allows you to:
- Personalize training intensity zones.
- Track fitness progress over time.
- Optimize performance when power data isn’t available.
If you don’t have your LTHR yet, you can still get started by using Max HR to calculate your cycling heart rate zones.
Setting heart rate zones from your LTHR
Once you know your LTHR, you can build personalized training zones around it. The most widely used system, developed by coach Joe Friel, defines five zones as a percentage of your lactate threshold heart rate:
| Zone | % of LTHR | Purpose |
|---|---|---|
| Zone 1 (Recovery) | Under 81% | Active recovery, very easy spinning |
| Zone 2 (Aerobic) | 81 to 89% | Endurance base, long steady rides |
| Zone 3 (Tempo) | 90 to 93% | Sustained moderate efforts |
| Zone 4 (Threshold) | 94 to 99% | Raising your sustainable pace |
| Zone 5 (Above threshold) | 100% and above | VO2 max and anaerobic work |
Because these zones are anchored to your own physiology rather than a generic maximum heart rate, they give a more accurate target for each session. Recalculate them whenever you retest your LTHR, since the number rises as your fitness improves.