Latest revision as of 18:10, 3 December 2011

This chart shows the perceived temperature while running based on a specific height, weight and pace. This calculator is based on my Running Heat Model.

1 Introduction

Normal heat indexes assume a person walking outdoors at 3 mph and generating 180 watts per square meter of skin. The original work states "higher levels of activity would increase the sensitivity to humidity… few people, however, sustain activity above the level considered here for long enough to reach a steady state". This is not very helpful to runners that are moving far quicker than 3 mph and generating a lot more heat.

2 Heat equivalent table

The table below shows an example set of equivalent temperatures for someone running 8:00 min/mile pace and is 174cm/70inches high and weighs 60Kg/132lbs. You can create a customized version of this table by filling in the form below

3 Notes

• For conditions where sweating is required to keep cool, temperatures shown are how hot it would have to be for you to sweat the same amount when walking.
  • The 'x% max' is showing what percentage of your maximum sweat evaporation is required to avoid heat build up.
• For conditions that are cool enough that sweating is required, temperatures shown are that have the same heat loss when walking.
  • The 'x Watts' show the estimated heat loss.
• Walking temperatures assume 30% humidity.
• The entries 'Too Hot' indicate that not enough sweat will evaporate to keep your internal temperature stable.
• When the conditions are too hot, the approximate time for your core temperature to rise to a critical point is given as 'Terminal in x'.
• This utility can also display sodium losses. The sweat rate shown is based on the assumption that all sweat evaporates; if sweat is dripping off you then your actual sodium losses may be far higher. For more details see Hydration 101.

4 Input Form

5 Impact of Humidity

The graph below shows how core temperature (of walkers) on the Y-axis rises with humidity on the X-axis for different air temperatures (lines). You'll notice that at 24f/75f there is no impact of humidity on core temperature. For temperatures between 33c/92f and 45c/113f, the humidity does not change core temperature until a critical point is reached and then there is a dramatic rise. By 50c/122f, even changes in very low humidity make a big impact on core temperature. It seems reasonable that a similar response would be seen in runners, but at lower temperatures.

The effect of heat and humidity on core temperature

6 Dew Point

Runners World suggested that dew point could be used in isolation, and published the simple table shown below. This seems an overly simplistic and flawed approach. For instance, at 3:51 pm 23 Jul, Phoenix, AZ was 105f with a dew point of 55f, which the table below would say is at the low end of "Comfortable, Hard efforts likely not affected". I believe that 105f, even with low humidity would not be comfortable and it would impact my performance.

7 Other Sports

This page is focused on runners, but may apply to some other sports such as soccer. It would not apply to cycling or similar sports where there is more air movement.

8 See Also

• Running calculators
  • Running Heat Model
  • Heat limited running pace
  • Optimum Running Temperature
• Running in the Heat
• Heat Acclimation Training
• Impact of Heat on Marathon Performance