Aerobic Decoupling & Cardiac Drift Calculator - Joe Friel Base Test
Evaluate your aerobic base readiness for marathons and century rides. Determine whether cardiac frequency drift indicates fatigue, dehydration, or pacing issues.
How to Use Aerobic Decoupling in 3 Simple Steps
Step 1: Upload
Drag & drop your .FIT, .GPX, or .TCX activity file. All processing is 100% private in your browser.
Step 2: Process
FitCrop inspects telemetry streams, removes anomalies, recalibrates metrics, or fixes binary checksums.
Step 3: Export
Download your clean Strava, Garmin, and Zwift compatible file with 1 click. Zero server wait.
Frequently Asked Questions
What is a good aerobic decoupling percentage for endurance?
According to sports scientist Joe Friel, a decoupling rate under 5.0% indicates that your aerobic base is rock solid. Over 5% signifies aerobic fatigue, dehydration, or premature pacing.
How is Efficiency Factor (EF) calculated?
Efficiency Factor equals normalized power (or speed) divided by average heart rate. Decoupling is the percentage decrease in EF between the first half and second half of your workout.