Half Ironman: Heart Rate (HR) Cycling Test at TrainingPeaks
Preparing for a Half Ironman (70.3) requires more than just logging miles—it's essential to understand your body and train based on reliable metrics . When you don't have access to a power meter, heart rate (HR) remains an excellent tool for measuring effort and guiding cycling training.
In this article, we explain how to perform a cycling heart rate test in TrainingPeaks, how to interpret the data, and how to apply it to your training plan leading up to the race.
Why train with heart rate?
While power is a direct output metric, heart rate provides an internal reading of the physiological response to exertion . With a simple heart rate monitor (HR monitor), you can:
- Assess the intensity of the actual effort
- Monitor accumulated fatigue
- Detect signs of overload or need for recovery
- Adapt training to your daily physical condition
What is Threshold Heart Rate (LTHR)?
Threshold Heart Rate (LTHR) represents the maximum heart rate you can maintain during prolonged exercise (typically 30 to 60 minutes) without becoming unsustainably fatigued. In cycling, this value serves as a basis for defining personalized training zones .
HR Cycling Test on TrainingPeaks
This test can be performed on the road or on a roller , as long as you have a reliable heart rate sensor and safe conditions to maintain constant effort.
Test structure (total duration: ~60 min)
-
Warm-up (15-20 min):
- 10 min easy pedaling (Z1-Z2)
- 3x1 min of moderate effort with 1 min of recovery
- 5 easy minutes
-
Main test (20 to 30 minutes):
- Pedal as hard as possible in a constant and controlled manner.
- Maintain a sustainable effort (as if it were a time trial)
- Record your average heart rate over the last 20 minutes
-
Cooling down (10-15 min):
- Easy pedaling until you return to zone 1
🧠 Important: Make sure you are well rested before the test and avoid strenuous training in the two days before.
LTHR Calculation
After the test, calculate your average heart rate for the last 20 minutes of the main session. This value will be your cycling LTHR .
Example: If the average HR over the last 20 minutes was 162 bpm , then:
📊 LTHR = 162 bpm
Heart rate training zones (Joe Friel model)
With your LTHR calculated, you can set up training zones in TrainingPeaks as follows:
| Zone | LTHR Percentage | Objective |
|---|---|---|
| Z1 | <81% | Active recovery |
| Z2 | 81–89% | Aerobic Base / Endurance |
| Z3 | 90–93% | Constant pace (Half Ironman) |
| Z4 | 94–99% | Threshold / Strong Time |
| Z5a | 100–102% | Low VO2max |
| Z5b | 103–106% | Average VO2max |
| Z5c | 106%+ | High VO2max / Anaerobic |
When and why repeat the test?
Ideally, repeat this test every 6 to 8 weeks , especially after a structured training block. This allows you to adjust your zones and ensure you're training at the right intensity for your current level.
Advantages and limitations of HR training
✅ Advantages:
- Easy to monitor with affordable equipment
- Reflects the internal state of the body (fatigue, stress, sleep)
- Useful for beginners or athletes without power meters
❌ Limitations:
- HR can be influenced by temperature, hydration, stress and caffeine
- There is a natural delay (lag) between physical exertion and cardiac response
- Does not directly measure “output” (like watts)
Conclusion
Heart rate- based training remains a valid and effective way to develop aerobic capacity for long-distance events like the Half Ironman . The HR cycling test in TrainingPeaks allows you to fine-tune your training plan, improve effort management, and avoid common mistakes like always training at the same intensity.
Remember: knowledge is power — and in triathlon, managing your effort well makes all the difference between surviving… or competing with confidence.
