Heart Rate Drift Calculator
First Half of Workout
Second Half of Workout
Your Heart Rate Drift:
0%
What is Heart Rate Drift (Aerobic Decoupling)?
Heart rate drift, also known as aerobic decoupling or Pa:Hr (Pace to Heart Rate ratio), is a physiological phenomenon where your heart rate increases over time despite maintaining a constant power output or running pace. In a perfectly efficient aerobic system, your heart rate should stay stable if the intensity remains steady.
How to Use This Calculator
To get an accurate measurement of your aerobic fitness, follow these steps during a steady-state workout (typically Zone 2):
- Perform a steady-state workout of at least 60 minutes at a constant intensity.
- Split the "work" portion of the file (excluding warm-up and cool-down) into two equal halves.
- Input the average heart rate and average power (or speed) for the first half.
- Input the average heart rate and average power (or speed) for the second half.
Interpreting Your Results
The resulting percentage tells you how much your efficiency "decoupled" during the session:
- ✅ 0% to 5%: This indicates a high level of aerobic fitness. Your cardiovascular system is well-conditioned for the duration and intensity of the test.
- ⚠️ 5% to 10%: This suggests moderate aerobic decoupling. You may need more base mileage or better hydration/cooling strategies.
- ❌ Above 10%: This indicates significant drift. Your aerobic base may not be sufficient for this duration/intensity, or external factors like heat or fatigue are significantly impacting your performance.
The Mathematical Formula
The calculator uses the standard industry formula for decoupling:
Drift % = ( (Ratio 2 – Ratio 1) / Ratio 1 ) × 100
*Where Ratio = Average Heart Rate / Average Power (or Speed).
Practical Example
Imagine you go for a 90-minute steady run:
- 1st 45 mins: Avg HR 140 BPM, Avg Power 200W (Ratio = 0.70)
- 2nd 45 mins: Avg HR 150 BPM, Avg Power 200W (Ratio = 0.75)
- Calculation: ((0.75 – 0.70) / 0.70) * 100 = 7.14% Drift