Aerobic Decoupling Calculator (Pa:Hr Cardiac Drift)
How much your pace-to-heart-rate efficiency fell from the first half of a steady run or ride to the second, from the average speed or power and heart rate of each half.
Results
What this tool does
On a steady aerobic effort your heart rate should stay level while pace or power holds. If heart rate creeps up, or pace drops for the same heart rate, the efficiency factor (speed or power divided by heart rate) falls, and that percentage drop is called decoupling or cardiac drift. Coach Joe Friel popularised it as Pa:Hr and suggests that under about 5 % over a long, steady session points to a well-developed aerobic base. Use a flat or evenly paced effort of at least an hour, because hills, heat, dehydration and caffeine all push heart rate up, and use power for cycling where you can, as it is steadier than speed.
Formula
EF = speed (or power) ÷ heart rate · decoupling = (EF₁ − EF₂) ÷ EF₁ × 100
Variables
| Symbol | Meaning | Unit |
|---|---|---|
o1 | First half: average speed (or power) | — |
h1 | First half: average heart rate | bpm |
o2 | Second half: average speed (or power) | — |
h2 | Second half: average heart rate | bpm |
DC | Aerobic decoupling (Pa:Hr) | % |
E1 | Efficiency factor, first half | — |
E2 | Efficiency factor, second half | — |
CL | How to read it | — |
Worked example
- First half: average speed (or power)10
- First half: average heart rate140 bpm
- Second half: average speed (or power)9.8
- Second half: average heart rate147 bpm
- Aerobic decoupling (Pa:Hr)6.7 %
- Efficiency factor, first half0.0714
- Efficiency factor, second half0.0667
- How to read it5 % or more — your heart rate drifted; endurance at this effort has room to improve
Limitations
- This tool is informational only. It does not diagnose, treat or replace a qualified health professional. Speak to a doctor before making decisions about your health.
- The default values are typical reference figures, not measurements of your situation. Replace them with your own data whenever you have it.