Heat and marathon pace reference
Enter your reference marathon pace in cool conditions and the environment. You will see a marathon scenario calculated with published means, without choosing a percentage yourself. It is a limited educational model: it does not predict your individual response.
The calculation is visible
Ely and colleagues (2007) published mean time differences from the course record across four WBGT intervals for top male finishers: 1.7%, 2.5%, 3.3% and 4.5%. We compare each mean with the cool interval: factor = (1 + mean ÷ 100) ÷ 1.017.
This transformation is an educational decision by Runi. The study did not validate this form, its combination with the environmental approximation or its use for an individual.
pace = reference pace × (1 + mean ÷ 100) ÷ 1.017
How the interval is assigned
The changes are stepwise, not a continuous curve. We round WBGT to one decimal, with cut points at 10, 15 and 20 °C; 5.1 and 25 °C are the strict limits of the tool. A small measurement difference near a cut point can change the output.
In climate mode we use the Bureau of Meteorology approximation, which assumes certain wind and radiation conditions. We add no invented corrections for sun, wind or acclimatisation, and chaining it with the means has not been validated as a predictor.
The pace is rounded to the second and the time is calculated from that displayed pace. The percentage uses the unrounded factor, so it may not match the change in the displayed pace exactly.
What it does not do
- It does not distinguish sex, age, level, acclimatisation, wind, sun or duration: there are no validated data to extrapolate those differences.
- Its scope is the 42.195 km marathon. It does not convert the result to 5K, 10K or half marathon.
- It does not assign safety colours or medical risk from an approximate index.
- It does not prescribe water or sodium and does not diagnose acclimatisation.
- The form limits are tool decisions, not safety thresholds.
Sources
The published means describe top male marathon finishers. They have not been shown to apply to recreational runners.
Frequently asked questions
No. It is an illustrative scenario calculated with published means from another group of runners. It is not an equivalent-effort pace or a safety clearance.
Because the published data cover a WBGT from 5.1 to 25 °C. Outside that interval we do not extrapolate. No estimate does not mean conditions are safe.
No. The scope is the marathon. Changing distance would require other data and other validation.
This is a calculator. Runi is a coach that decides with you what each day calls for.
Tell Runi your goal and any aches, and your plan adjusts to you.
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