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The runner’s paradox is that he or she always wants to run, but there are environmental or physical conditions that require precaution.
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Outdoor temperature is only one parameter; the perception of heat also depends on humidity and solar radiation.
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The WBGT index assesses several variables, but individual endurance and personal feelings are important in deciding when to run.
The paradox of the runner is that he would never stop running. It is a paradox because instead common sense would have it avoided under certain circumstances. The reasons are quickly explained: there are environmental or physical conditions that should convince even the most motivated runner or the most convinced runner that, just this once it is better to let it go. The physical ones are related to injuries, whose full recovery is often neglected because “I can’t stand still anymore.” Environmental ones, on the other hand, are more variable: one of the most conditioning situations is definitely heat. Why do I say they are variable? Because every body reacts differently to heat, especially when it is more intense.
The thermometer doesn’t tell you everything
As we have already explained, temperature provides a reference value that has to be read in relation to other parameters: an outdoor temperature of 32°C may be tolerable or intolerable depending on the percentage of moisture in the air, causing our body’s perception of heat to fluctuate greatly. In short, the absolute value is a relatively significant index and should always be cross-referenced with other parameters in order to obtain as accurate a prediction of temperature perception as possible.It should also not be overlooked that there are other parameters that influence performance in hot conditions: not only air temperature matters but also the radiation caused by the reflection of the sun on asphalt or, in general, on outdoor surfaces. You will have realized that it is not easy to establish unambiguous parameters, and it is no coincidence that this is still a much-studied topic because it does not only concern those who practice sports: one of the sectors that first became interested in it is, for example, the military, in order to understand and establish parameters within which it is considered safe to carry out exercises. https://runlovers.it/2018/fa-caldo-quando-e-come-correre/
How do we cool down?
Every body has an operating temperature, that is, a range within which it operates normally or, having exceeded minimum or maximum values, begins to go into crisis or worse. In the case of the human body, the range is 36.5° to 40°. I am well aware that now you will object: generally men with a fever of 37° are already delirious and that is VERY TRUE, however, we understand each other. By staying within these values we function “normally.” I use quotation marks because it is clear that with a fever of 102 you don’t go running. The higher the body temperature rises, the more it accelerates the exchange of heat with the outside world through sweat, which is deposited on the surface of the skin and, as it cools in contact with air, allows the body to exchange heat with the outside world and cool itself. The higher the humidity in the air, the more difficult it is for this exchange to occur, partly because sweat cannot dry and evaporate. This is why the perceived temperature is closely related to humidity: the higher this is, the hotter you will feel, even at the same temperature. Finally, consider that sweat evaporation is also affected by air temperature: above 42-43 degrees even a breeze will not allow sweat to leave and thus cool your body (but then again, who runs in those temperatures? Here). https://runlovers.it/2013/gli-effetti-del-caldo-sul-corpo/
Wet Bulb Globe Temperature
To give you an idea of how complicated the subject is, an index called Wet Bulb Globe Temperature or WBGT has been used for many years. This is a value obtained by processing several parameters such as direct irradiance, humidity, wind speed, sun angle, and the possible presence of clouds. So is it enough to consult this index to decide whether to go running in hot weather or not? Eh, if it were that easy. Even the WBGT does not give unambiguous guidance because then, in the end, it depends on the individual: each person has or does not have resistance to running in extreme conditions.
Okay, but then when can I run?
The wise thing to do is to rely on your feelings. If after you’ve been running for a while you feel heavy headed, have exhaustion or dizziness, feel like the temperature is intolerable stop running. Start walking and return to base or stop for a moment and then return home. Assuming that you protect your head (the part of your body most exposed to the sun and the part that proportionally exchanges the most heat with the outside), also consider that in hot weather your “normal temperature” performance decreases by up to 20 percent, so it is perfectly normal to go slower. The more you speed up or the more you try to maintain your normal pace, the more your metabolism speeds up to support your running, developing even more heat. By slowing down you therefore have the advantage of developing less heat. Finally: hydrate as much and more than normal (since you will lose much more fluid in the run) and favor the early hours of the day: it is true that temperatures drop in the evening, but the heat component returned from the ground to the atmosphere peaks, after having accumulated throughout the day. If the heat comes on suddenly, be aware that the body is not immediately ready to function in changed environmental conditions: in fact, acclimatization takes 7 to 14 days. Running is fun. If it becomes a pain, it is really not worth it anymore. (Photo credits ringsaroundme)