INTERPRETING RESULTS
A negative decoupling result: what to check first
A negative number means the speed-to-heart-rate ratio increased under this convention. It is a starting point for reviewing the run.
Read the sign convention
The public tool calculates 100 × (first efficiency − second efficiency) ÷ first efficiency. When the second ratio is larger, the subtraction is negative. Another product may use a different sign convention, so check its definition before comparing outputs.
The formula alone does not explain why the ratio changed. It cannot distinguish a steadier effort from a downhill section, a tailwind or an unreliable heart-rate trace. There is no automatic “better than zero” interpretation built into the calculator.
Calculate a simple negative example
The numbers in this example are illustrative, not a customer training record.
| Input | First half | Second half |
|---|---|---|
| Pace | 5:00 min/km | 5:00 min/km |
| Heart rate | 150 bpm | 140 bpm |
| Distance per heartbeat | 1.333 m | 1.429 m |
Using unrounded ratios, decoupling is 100 × (1 − 150 ÷ 140), or approximately −7.14%. Heart-rate drift is 100 × (140 − 150) ÷ 150, or approximately −6.67%. Rounding the ratios to three decimals before calculating would introduce a small difference.
Review selection, pace and sensing
First, check whether the first half begins during a transition such as a fast start. Second, inspect whether the second half has easier terrain or a changed pace. Third, look at the heart-rate trace rather than relying only on its average. A lower average caused by gaps or a tracking error is not the same as a lower heart rate throughout a comparable interval.
Keep elapsed duration and pause handling consistent. A short walking or standing break can affect the relationship between average pace and average heart rate. The tool accepts the inputs; it cannot validate the underlying workout.
Keep an observation with the number
Try the example in the aerobic-decoupling calculator, then change one input at a time. Notice how faster second-half pace can also make decoupling more negative when heart rate stays the same.
Save a short observation such as “second half downhill” or “same flat loop, uninterrupted.” That context is more useful than giving every negative value the same training interpretation.