FREE RUNNING TOOLS
Aerobic decoupling calculator
See how the pace-to-heart-rate relationship changes between two comparable halves.
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Example result
- Aerobic decoupling
- 4.76%
- Heart-rate drift
- 5%
- First half · Distance per heartbeat
- 1.429 m
- Second half · Distance per heartbeat
- 1.361 m
How it works
For each half, efficiency is speed ÷ heart rate. Decoupling is 100 × (first efficiency − second efficiency) ÷ first efficiency. Positive means the ratio decreased; negative means it increased. Heart-rate drift is 100 × (second heart rate − first heart rate) ÷ first heart rate. It does not account for changing pace.
Choose equal-duration, steady segments after warming up. Hills, stops, weather changes and sensor gaps can dominate this comparison. A percentage alone does not establish an aerobic threshold.
Worked example
At 5:00 min/km in both halves, with heart rate rising from 140 to 147 bpm, heart-rate drift is 5%. Decoupling is 100 × (1 − 140 ÷ 147) = 4.76%. The two percentages answer different questions.