Heart rate
Heart-Rate Drift Calculator
Use this after a steady easy run. Enter first-half and second-half pace plus average heart rate to see whether the internal cost rose.
- Compares efficiency between two halves of a steady run.
- Works best on flat, even-effort easy runs.
- Large drift can reflect heat, fatigue, dehydration, or aerobic base still developing.
Heart-rate drift shows whether the same running output became more expensive later in the run.
- Use a steady easy run, not intervals.
- Enter average pace and heart rate for each half.
- Avoid runs with long stops, big hills, or major wind changes.
Around 0-5% is usually a controlled result. Higher values can point to heat, dehydration, fatigue, or aerobic fitness that still needs more easy volume.
- Repeat the test in similar weather.
- Slow down or shorten the run when drift is high.
- Use a chest strap if the watch trace looks erratic.
Use the result as a recovery and aerobic-base clue, not as a race prediction.
Heart-rate calculators Heart-Rate Zone Calculator Estimate easy, steady, and hard running zones. Heart-Rate Drift Calculator Estimate aerobic decoupling from a steady run. Max Heart Rate Calculator Compare age estimates with observed hard-effort readings. Heart Rate Reserve Calculator Use resting and max heart rate for personalized ranges. LTHR Zone Calculator Calculate zones from lactate threshold heart rate.
Did my heart rate drift too much?
Aerobic decoupling 5.4%
Moderate drift
This compares pace-to-heart-rate efficiency between the two halves. Use it only for steady runs with similar terrain, effort, temperature, and hydration.