AVERAGES AND UNITS
Why whole-run averages can disagree with segment efficiency
A ratio calculated from two averages is not generally the same as the average of two ratios.
Start with matching time windows
The running-efficiency tool divides speed by heart rate after converting the units. It cannot tell whether the two inputs came from the same part of the activity. Pairing moving pace with heart rate averaged over both movement and stops can produce a tidy number with an unclear meaning.
Choose a common interval and use its duration, distance and heart-rate coverage consistently. If the watch reports an average only across valid sensor samples, check whether that coverage represents the whole interval. Missing readings should not quietly stand in for a normal heartbeat count.
Follow two equal-duration segments
The numbers in this example are illustrative, not a customer training record.
| Measure | Segment A | Segment B |
|---|---|---|
| Speed | 180 m/min | 240 m/min |
| Average heart rate | 120 bpm | 180 bpm |
| Distance | 1800 m | 2400 m |
| Estimated beats from these averages | 1200 | 1800 |
| Distance per heartbeat | 1.500 m | 1.333 m |
The simple average of the two segment ratios is about 1.417 m per beat. But the combined totals are 4200 metres and 3000 beats, giving 1.400 m per beat. Equivalently, average speed is 210 m/min and average heart rate is 150 bpm: 210 ÷ 150 = 1.400.
Understand the weighting
The combined ratio gives more weight to the segment containing more heartbeats. An arithmetic average of the two ratios gives the segments equal weight. Neither operation should be hidden behind an unexplained label such as “average efficiency.”
Different-duration segments add another issue: averaging their speeds equally no longer gives the overall speed. Use total distance divided by total elapsed time for the chosen moving interval. In the example, the segments are deliberately equal in duration so that the difference comes from the ratio calculation itself.
Keep the public calculation in perspective
Use the running-efficiency calculator for a transparent summary of matching inputs. The tool works with the summary values you enter; the activity view provides additional context from your recording.
When a public result and an app summary differ, check the window, averaging method, units and exclusions before deciding that one is wrong. A numerical difference can come from a different question being asked of the same run.