If you train with heart rate, your Lactate Threshold Heart Rate (LTHR) is one of the most useful numbers you can know. Use the calculator below to turn your cycling LTHR into practical training zones you can use on road rides, indoor sessions, and structured workouts.
Cycling LTHR Zone Calculator
Enter your tested cycling LTHR, or the average heart rate from the last 20 minutes of a 30-minute time trial.
Use this if you have previously tested and confirmed your cycling lactate threshold heart rate.
What is LTHR in cycling?
LTHR stands for Lactate Threshold Heart Rate. In simple terms, it is the highest heart rate you can sustain steadily for around an hour without rapidly fatiguing. In practice, most cyclists estimate it using a shorter field test, then use that value to define training zones.
Compared with generic “220 minus age” formulas, LTHR-based zones are usually much more useful because they are tied to your current fitness and your own physiology.
How to test your cycling LTHR
30-minute field test (common method)
- Warm up 15–20 minutes with a few short efforts.
- Ride a hard, steady 30-minute time trial effort.
- Record your heart rate for the full effort.
- Take the average heart rate from minutes 10–30 (last 20 minutes).
- That number is your estimated cycling LTHR.
Try to test under similar conditions each time: same bike setup, similar temperature, similar hydration, and similar caffeine routine.
Indoor vs outdoor testing
You may get slightly different values indoors and outdoors. Indoor sessions can run hotter and elevate heart rate drift, while outdoor tests may involve coasting or terrain changes. If possible, keep separate notes and use the value most relevant to your main training environment.
How to use your zones
Once you calculate zones, assign workouts by intent:
- Recovery rides: Keep heart rate low (Zone 1).
- Aerobic endurance: Build durability in Zone 2.
- Tempo and sweet spot support: Use Zone 3 for controlled sustained work.
- Threshold development: Spend intervals around Zone 4.
- High-intensity work: Use Zone 5a/5b/5c for specific race demands.
LTHR vs FTP vs max heart rate
LTHR (heart-rate based)
Best for pacing steady efforts and managing training load when power data is unavailable or unreliable.
FTP (power based)
Directly measures external work output and is usually preferred for precise interval targeting.
Max heart rate
Useful context, but not ideal as the sole basis for training zones because two riders with the same max HR can have very different threshold and endurance profiles.
Common mistakes cyclists make
- Using running LTHR for bike workouts (cycling LTHR is often lower).
- Testing when overly fatigued, sick, or dehydrated.
- Treating heart rate as instant feedback in short efforts (it lags behind power).
- Never retesting after fitness changes.
- Ignoring heat, altitude, and life stress, all of which can shift heart rate response.
When should you retest?
A good rule is every 6–10 weeks during focused training blocks, or after major changes in fitness. If your normal tempo rides feel too easy or threshold intervals feel impossible at old targets, it is probably time for a retest.