This tool calculates heart rate drift to help determine your Aerobic Threshold (AeT), following the Uphill Athlete methodology. After a warmup, run on flat ground for 1 hour at a pace you think is close to your upper aerobic limit and record the workout with a GPS watch. Download the TCX file from your fitness tracking website (Garmin, Fitbit...) and upload it here. Zoom on the plot to the interval where you ran at steady pace. The table will show your calculated Pa:Hr drift, pace, heartrate, and other metrics for that interval.
You ran close to your AeT if your Pa:Hr drifted by 5% over an hour. The Pa:Hr drift compares the Pace-to-hear-rate ratio (pace in km/h) of the first half of the selected interval to the second half. A value of 5% means that you ran on average 5% slower at constant bpm during the second half, or your heart rate was 5% higher at constant pace. This metric is sometimes referred to as Cardiac Drift or Aerobic Decoupling.
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Built by Douglas Watson, 2020. Source code on github. MIT License.