During training runs, with the exception of extremely cold or hot days, maintaining body temperature is not a crucial part of the workout. The point of a workout is to stress the body. Working harder when the weather is less than ideal allows the body to acclimatize to either hot or cold weather conditions. However, On unusually warm days one should still pay a particular attention to the heat index to prevent overheating.

Being aware of your body temperature can be critical to one’s success during a race. Your body will use more energy trying to maintain its core temperature in extremely hot or cold temperature. If you actively help maintain your bodies temperature, that energy can be then applied to the effort of the race, instead of using the energy to heat or cool your body.

Studies have shown the mid-50s are the most efficient temperature to run in. There is a host of other factors, such as humidity and wind to consider. A 70 degree day with very high humidity can act and feel much hotter than a 70 degree day with no humidity and a light breeze. 

The Body.

The body generates its own heat. All exercise can raise the core body temperature. The more vigorous the exercise, the more heat that is generated. This core temperature can rise several degrees over the course of the workout.

As the core body temperature rises, the body will take steps to maintain its core temperature. The primary method is through the use of sweating. When one sweats, moisture is produced which allows for evaporation, which in turns cools the skin. If everything is working properly, as one works harder the more one will sweat which in turn allows for even more evaporation.

It is necessary to examine how evaporation works. Cooling occurs when the liquid water your body produces is turned into water vapor. There are several factors that influence this process. The most obvious one is how hot it is the air temperature. When temperatures are higher outside the rate of evaporation increases.

Related to that is the temperature of the liquid. The higher the temperature of the liquid, in this case, sweat, the higher rate of evaporation. The next vital factor is the outside relative humidity. The higher the humidity, the lower the rate of evaporation. It becomes increasingly difficult to add more water to air already containing more water moisture. It is also one of the reasons why it feels hotter on humid days.

Another factor is how much liquid your body produces. As it gets hotter, more liquid is needed for more evaporation.

If you maintain a proper ratio of liquid intake to sweating, theoretically you should be able to maintain your body temperature indefinitely.

Another factor is humidity. On extremely humid days, evaporation from the skin is more difficult. On extremely dry hot days, the opposite problem occurs. As the water evaporates quickly, it will not allow for the conduction phase of the evaporation to occur. Conduction is the cooler water transferring, the lower temperature back to the body.

Another process is called convection. This is a factor of the air blowing over the body. Ironically the faster you run, the more efficient your body becomes at cooling itself. Conversely, if one is getting too tired and hot and they come to a complete stop, then there is less air is flowing over the body. This will cause the body temperature to rise even further. This is a crucial concept. If you come to a complete stop to recover, you may increase your bodies core temperature thus pushing yourself into heat exhaustion.

Each factor plays a part in maintaining your body temperature. The first part is how much you sweat, which can vary from person to person. You will produce a greater amount of sweat the hotter your body temperature is which in turn helps maintain the core temperature at a lower level. Understanding how the body tries to regulate its temperature is noteworthy because it will influence how to prepare for both hot and cold conditions. It is necessary to understand each of above factors to help determine the best course of action.


There are multiples ways to influence your body temperature in the heat. On hot days, the first rule is to make sure you are properly hydrating yourself. Be aware the hotter the temperature, the more you will need to maintain your liquid intake. Besides evaporation, the other way to cool your body is through the use of conduction. Simply pouring water on the top of the head and down the back of the neck can help keep the body cool. For women that have longer hair, it is best to leave your hair down as the water in the hair will act as a heat sink and will not dissipate as quickly. On especially hot days bring a bandana, or other cloth that you can use as a wet a drape around your neck. 

In the early stages of the run, if you are sweating properly and it is not too hot do not dump water over the entire body. But be careful, Cold water can interfere with the evaporation process. Confine the water you pour on yourself to your head and neck area. Most of the blood will circulate through the main arteries in the neck. This is one of the reasons to keep your neck cool.

In weather, hotter than normal, slow your pace down from the onset. The amount you slow down is based on how hot the temperature will be in the latter stages of the race. Do not wait for your body to become overheated.
Waiting too long to slow down will cause you to slow down 3-4 times more than if you picked the right pace from the beginning.

The choice of clothing is also crucial. Darker clothes absorb more heat than lighter colors. Also, pay attention to the fabric. On extremely hot humid days, you want a fabric that will whisk moisture away from the body and allow for maximum convection. Consider clothing that expose more of the arms such a tank top or singlet.  On extremely hot dry days,  consider wearing more, not less coverage. Unlike hot, humid days, the rate of evaporation exceeds the body’s ability to produce water. It is counter-intuitive but examine how the Desert Bedouin dress. They cover most of their body. The fabric they wear allows for the water to remain on the skin for longer periods of time. In extremely hot and dry conditions wearing a legionnaire hat can be beneficial. This hat has a flap/neck drape that one can constantly dump cool water over to help maintain a lower body temperature.


Cold is much easier to deal with than heat. Simply wearing a heavier fabric with Long sleeves or adding another light layer of clothing is usually sufficient for most races. The body generates heat. With this added layer, there should be enough heat to trap against the body. If the race is in very cold conditions, then dressing in additional layers should be considered. Be aware that most heat is lost through the heads and hands. In very cold conditions, light gloves to protect your hands are a must. Consider bringing a Thermal hat made of fleece or wool.

When adding clothes, it is necessary to dress in a fashion that one can moderate one’s temperature as they run. For instance, if you are wearing a windbreaker make sure there is a zipper that can be opened up. Consider using a long-sleeve shirt that is loose enough to able to be pushed or rolled up to expose your arms.


A person that is coming from a winter climate will be more uncomfortable in a race conducted in 70 degree temperatures than a runner that comes from the desert that was training in high temperatures. This link documents the effect. . The general consensus is it takes about 14 days to acclimate properly. Generally this concept applies to the extreme temperatures on both end of the scale.

Most of the tips that are given here are to be used during race conditions. During the short training runs, with the exceptions of very hot or cold days, it usually is not necessary to try and mitigate the heat or your body temperature. The run is usually over before your body temp can rise too far. So in effect one can practice acclimatization with out too may adjustments.

The Race 

Hot conditions.

There is not a single approach to planning a race. There is a host of factors such as conditioning, acclimatization, race day conditions and other factors to consider. To find the best approach one needs to find the weather report and then set up a personal game plan.

These are some factors to consider.

1, Temperature prior to the race.

2 Temperature at the start of the race.

3, Temperature at the later stages of the race.

4 The heat index.

5 Wind conditions.

6. How heat affects you personally.

7. How acclimatized you are to the weather conditions

The above factors will allow you to dress properly for the race. For instance, if the heat index is high with very high humidity then wearing an outfit that allows your body to sweat is very important.On a bright, hot sunny day, then wearing a light colored top is imperative. If the morning temps are cool, then it is better to dress in layers and dispose of the top layer as the body temperature rises.

Proper Hydration is the single most crucial factor that is in your control. There is a difference between proper hydration and over-hydration. Stocking up on too much water prior to the race is not only counterproductive it can be down right dangerous and lead to Hyponatremia. Hyponatremia can be more of a factor on hot days the heat exhaustion. In fact, it is often misdiagnosed. Never stock up on water prior to a race and follow the rule drink to thirst.
Hyponatremia is invariably a condition that is self-inflicted.
Prior to a race, the adrenal glands will kick in which will in turn divert the blood to the extremities. This is  the primary reason so many people desperately need to use the restroom prior the race. A vicious cycle is now being created. By urinating more than normal before the race, can deplete the proper Salt/potassium balance. Which cause more thirst, which then causes you to drink more water, which in turn makes you even more thirsty.

Most runners will only experience premature fatigue. They just think they have an off day or weren’t trained properly. However, this can cause severe health problems and even death. In some studies, some of the deaths that have occurred in marathons were attributed to water poisoning(Hyponatremia), not heat stroke.

On potentially hot day, it is a good idea to bring a water bottle to the starting line. A few small sips in the minutes before the race can be beneficial. Avoid “stocking “up in the hours before a race.

On a very hot day, It is necessary to adjust your expectations. For example, if the temperature is over 80 degrees and you run a 9-minute mile you could reasonably expect your time to drop by a minute a mile. If you are facing a hot day, slow down before you start feeling heat. Remember, your core body temperature is also a function of how hard your body is working. If you keep the pace slower than originally planned, you can forestall the negative effects of the heat.

As a loose guideline, expect your pace to drop by 20 seconds per mile for every 5-degree rise in the heat index. This calculation is  for runners in the 4-hour range. Runners in the 3-hour range may see only 10 second drop while runners in the 5 hour plus range may see a drop of 30 seconds or more per mile.

If you can make that compensation early in the race, you will have an overall net gain in time compared to runners that ignore the effects of the heat.

Conditions can change during the race. Be aware of those conditions and be flexible enough to change. Temperatures will generally rise as the race progresses. If you are running close to your max capability early in the race, be aware that this factor alone may be enough to send you into a downward spiral.

It is possible that you may not keep up with the hydration to keep yourself sweating properly. Be aware of this. If the temperature has not dropped, and you are not sweating as much as before then you may be heading for trouble. To mitigate the effects of less sweating, when you come to an aid station dump more water over your entire body, not just your head. Instead of evaporation, the body can now be cooled through conduction. Look for spray areas and try and keep your clothing doused with cool water. Many people offer water along the course. Take advantage of this. Slow down.

Aid Stations

During the race, aid station will usually be placed at or near every mile marker. On a warm to hot day, it is essential to use these early in the race. For example, if the heat index of the race is over 70 degrees it is best to start using these stations by mile 2. Water is almost always the first drink that is offered. Grab the first cup and dump it on your head and neck. This helps with the conduction phase of cooling. The next cup you grab is the liquid you will drink. Many marathons also supply a sports drink. It is vital to find out which drink are being offered so you can sample it in advance of the race to make sure your body is OK with it. In the early stages of the race, your body may only want a sip or two. If it is exceedingly hot, it may be necessary to take more than one drink at each aid station. For some people that incorporate walk breaks, this may be the perfect opportunity to walk.

But be careful!

If your walk is significantly slower than the run, be aware that one’s body temperature may rise during the break. This is because of the convection effect. By standing or walking slowly, there is less air moving over the body. Less flowing air reduces the amount of evaporation, which in turn cause the body to heat up. One trick that does not take up too much energy is move your arms away from your body. While you are walking, slowly move your arms in large circles. By doing this, you create  air flow over your body.

As the race progresses, it is essential to monitor your condition. Finishing the race is always the goal, but your health is always more important. Heat Exhaustion and Heatstroke can be deadly. Both can occur in runners that are in excellent shape that ignored the symptoms.


Heat exhaustion

During a hard run or race, we are often pushing our bodies to the max. This effort can raise our core body temperature several degrees.

If you add high temperatures and humidity coupled with the lack of water, or host of other factors one can push their body into dangerous areas. Everyone should be aware of the signs of heat exhaustion. Not only for themselves but also for their fellow runners around them.

Below is a list of warning signs to watch out for.

  • heavy sweating
  • paleness
  • muscles Cramps
  • tiredness
  • weakness
  • dizziness
  • headache
  • nausea or vomiting
  • fainting

The skin may be cool

It is crucial to pay attention to the above symptoms. During a race, these symptoms tend to be progressive. If your symptoms progress past the point of cramping and feeling weak, it is time to stop and seek help. Pushing your body further can lead to serious consequences.

Heat Stroke

Heat stroke is a dangerous and potentially fatal condition.

The body has lost all ability to self-regulate itself. A person suffering from heat stroke is past the point of being able to self-monitor or help themselves. Any person suffering from heat stroke will need immediate medical assistance. Many of the symptoms mirror those of Heat Exhaustion. The difference is these symptoms tend to be more severe. One significant difference is the color of the skin. Instead of being cool and pale the skin may appear hot, red and dry. A person in this state needs more than a cup of water and rest. They need medical assistance. If you observe a person in this condition, then it is necessary to call 911. 

 Hyponatremia (water poisoning)

Hyponatremia is another potentially dangerous and even deadly condition. A simplistic description of hyponatremia, is overhydration. Hyponatremia while running, occurs because too much water is being consumed. Sodium,potassium and other electrolytes aren’t in proper balanced with the water in one’s system. Ironically this overabundance of water causes one to be more thirsty.

Some of the symptoms of hyponatremia are similar to Heat exhaustion such as headaches and vomiting. The one symptom that truly stands out on the onset is bloating. For example, it may be impossible to remove rings from the fingers of a person suffering from Hyponatremia. Hands and other extremities can be visibly swollen.

Hyponatremia is entirely avoidable. Do not stock up on water before a race. Normal hydration is suitable. If you are running on an unusually hot day, make sure mix your water intake with sports drinks or food that contains salt and complex carbohydrates.

Early in the race moderate your water intake. Take sips of water. Listen to your body. If you take a sip or two of water early in the race and your body does not appear to want more then don’t stock up. The rule is to drink to thirst.

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