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[[File:Running In The Heat M.jpg|right|thumb|500px|Running in the heat is far more stressful and can be dangerous.]]__NOTOC__Running in the heat is much harder than running in cooler temperatures, reducing performance and creating serious health risks. Moderate exercise The simple guidelines are to slow up and avoid pushing the pace, drink to thirst, and to dress for the conditions. =Guidelines for Running in the Heat=# '''Don't die'''. Running is generally a pretty safe sport, but there are some serious hazards to running in mild temperatureshot conditions. #*''' Heat stroke. '''If your core temperature gets too high, you can suffer from heat stroke. Runners who get heat stroke typically ignore the warning signs, and push on until they collapse. Risk is higher with shorter distances and faster paces, such as 60f5K where the rise in core temperature can be extremely rapid, but can happen at the marathon distance as well. The key to avoiding heat stroke is to take it easy and don't push hard (see below on "go slower"), especially if you're new to running. You should watch out for the warning signs of overheated listed below. Note that some antidepressant medications have been linked to heatstroke.#*''' Dehydration. '''Contrary to expectations, it's really tough to die from dehydration unless you're running in a remote location. A runner died from dehydration in 2004, but they were running in the Grand Canyon in July where the temperatures can hit 120f in the sun. If you have access to drinks, dehydration is self-limiting. Contrary to popular belief, which has been promoted by the sports drink industry, the evidence is that mild dehydration (<=4%) doesn't impact performance<ref name="Goulet2012"/><ref name="Goulet2011"/15c>. See [[The Science Of Hydration]] for details. #*''' Hyponatremia. ''' Unlike dehydration, drinking too much is far more likely to be fatal. This condition, called [[Hyponatremia]], has killed a number of runners over the years. Drink to thirst and keep your salt intake high. Adding 1/4 teaspoon of salt to each quart/liter of drink helps offset the electrolyte loss (most sports drinks don't contain enough salt to be noticeable.) Be careful about drinking cold drinks to lower your body temperature, as this can lead to overdrinking. See [[Practical Hydration]] for details. #*''' Sunburn. ''' Not only does sunburn cause long-term health issues, it can also cause more immediate problems with your body's temperature control. Burned skin doesn't sweat so well in the heat, and in colder conditions burned skin can't contract the capillaries to reduce heat loss. # '''Adapt'''. There are various changes you can make to your running that will reduce performancemake summer running easier. #*''' Go slower. '''With increased heat stress, you'll be slower. In fact, but the perception optimum temperature for performance is generally about 40f/5c, and temperatures above this are likely to be fatigue slow you down. With mild temperatures (40-70f/5-20c) you're more likely to feel tired rather than hot as your mind shuts down muscle recruitment to prevent overheating. More extreme exercise or At higher temperatures , the impact becomes steadily greater. See [[Impact of Heat on Marathon Performance]] for some guidelines on how much heat changes pace.#*''' Acclimate'''.''' '''With acclimation, you will do better in the heat, though you'll never do as well as you will in cool conditions. Heat acclimation produces many benefits, including increased blood volume, more rapid onset of sweating, reduced electrolyte levels at moderate sweat rates, and more. See [[Heat Acclimation Training]] for more details#*''' Take breaks'''.''' '''Taking [[Walking Breaks]] can provide time to cool off, allowing you to maintain your training distance. Running a short route repeatedly can give you access to drinks and ice, as well as providing a natural break. You can check for [[Blister Prevention| blisters]] which can create be more of a problem in hot conditions. If you're looking to do speedwork, [[Interval Training]] is far better than tempo runs as the rest period between intervals allows you to cool off. However, be cautious with faster paced intervals like [[Tabata High Intensity Interval Training| Tabata HIIT]], as the faster pace can cause your core temperature to spike dangerously high. #*''' Avoid the heat'''.''' '''Run in the cooler parts of the day such as early morning and later in the evening, avoiding late afternoon. Also aim to avoid the sun both by running shady routes and choosing the risk right time of day. (Remember sunburn not only has long term health risks, it also reduces your ability to control your core temperature.) # '''Dress for the conditions'''. What you wear can make a big difference to your performance, comfort, and even safety. However, you have to dress for the conditions, as the humidity and sun change things. Running in high and low humidity conditions is rather different. Evaporation will help keep you cool in low humidity, but it's quite ineffective when the humidity is higher. (In the notes below, low heat illnesses is roughly <85f/30c, moderate is 85-100f/30c-40c, extreme is >100f/40c, though details will depend on your height and weight, as noted in [[Running Heat Model]].)#*''' Moderate heat with low humidity'''.''' '''When the humidity is low, evaporation will help keep you cool. Thin, form fitting clothing like [[Under Armor Heat Gear Top| UA's heat gear]] can spread out sweat over a greater area and keep you cooler than bare skin. #*''' Extreme heat with low humidity'''.''' '''When the heat becomes more extreme your sweat rate may not be sufficient to keep you cool. Under these conditions it becomes worthwhile to wear thicker clothing that will hold more water and spray yourself off. At [[2014 Badwater 135| Badwater]] I wore a loose long sleeved shirt that I kept soaked, which made a huge difference. When the heat is above core body temperature, air movement over dry skin will heat rather than cool your body, so it's only when you're wet that wind will help. #*''' Low heat with high humidity'''.''' '''These conditions can be dangerousdeceiving, as the overall heat stress is much higher than you might expect. When the humidity is close to 100%, even small changes of temperature have a big impact on the fastest pace you can maintain without overheating. Cooling in these conditions comes predominantly from air movement across your skin (convection), not evaporation. Your best option is to wear as little as possible in order to expose your skin to the air, and clothing can easily act as an insulator. If you need to cover up because of the sunlight, then wearing very loose fitting clothes that don't interfere with air movement may be an option. Ideally this loose clothing may act as a radiator for the heat, though in practice this is hard to achieve. Consider thin, form fitting clothes as another approach, but it needs to be as thin as possible. Consider applying ice to provide direct cooling (see below). Wind will help cool you off. #*''' Moderate heat with moderate humidity'''.''' '''The combination of the heat and humidity can be both brutal and intractable. The humidity limits the cooling from evaporation and the warm air limits the cooling from convection. In these conditions, applying ice is one of the few ways of cooling off, and without it running can become impractical. Clothing should be selected to spread out the meltwater from the ice, so thin, form fitting clothing is ideal. #*''' Extreme heat with high humidity'''.''' '''These conditions are relatively rare, but there comes a point where running becomes impractical and ill advised. #*''' Daytime'''.''' '''As you probably know, white clothing reflects heat where black absorbs heat. If you're in direct sunlight, then wearing white is critical, and even in partially shady conditions white clothing is an advantage. A white hat should be used, and consider a 'legionaries cap' to help protect your neck and face. See [[Running Hats]] for more details.#*''' Nighttime'''.''' '''After dark it may be better to wear dark clothing to help radiate more heat.
=Heat and Fatigue=
It is generally accepted that exercise at a constant effort will be voluntarily terminated once the core body temperature reaches about 40c/104f<ref name="Tucker-2008"/>. However, if subjects are allowed to vary their pace freely, they will preemptively reduce their exercise intensity to prevent their core temperature form reaching the critical point<ref name="Tucker-2008"/>. One mechanism for this reduction is that fewer [[Muscle|muscle fibers]] are recruited in hot conditions, even before the core body temperature starts to rise<ref name="Tucker-2004"/>. Elevated core temperature reduces the voluntary maximum force generated, though it is unimpaired when electrical stimulation is used, indicating the central nervous system is responsible<ref name="Nybo-2008"/> . When exercising at a constant [[Rating of Perceived Exertion]], subjects steadily reduced their power output at 59f/15c, 77f/25c or 95f/35c even though their perception of their temperature comfort remained constant<ref name="Tucker2006"/>.
==Mechanisms==
Exercise in the heat burns more carbohydrate than in cool conditions<ref name="Mündel-2008"/> . However, it is not clear to me if this is because of a direct change in the use of carbohydrate, or if the hot conditions reduce [[VO2max|V̇O<sub>2</sub>max]] and therefore the exercise intensity is effectively increased. Exercise in the heat also burns more muscle [[Protein]]<ref name="Snow-1993"/><ref name="Marino-2001"/>, and the waste products from this [[Protein]] metabolism could result in mental fatigue due to a rise in [http://en.wikipedia.org/wiki/Gamma-Aminobutyric_acid GABA]<ref name="Mündel-2008"/>.
=Hyperthermia - Heat can killStroke=Running in the heat can kill, as the body's protective mechanisms that normally cause us to slow down can be ineffective. There are a number of risk factors for serious heat injury stroke.
# Being overweight, as fat can act as an insulator.
# Being untrained, as fitness gives some heat adaptation over the unfit.
# Having suffered from heat illness before.
# Ignoring warning signs (see below).
Being overweight, unfit and attempting to run hard can be a catastrophic combination. Intense exercise can spike your core temperature and this rise can continue even after collapse as the heat from the muscles warms the blood while the fat reduces the cooling effect. =Staying Alive in the Heat - The Warning Signsof Overheating=
The best advice seems to be to take things cautiously if you are not used to running in the heat. Pushing yourself harder than normal in familiar heat, or attempting to run normally in heat you are not used to is dangerous. Traveling to a warmer area for a race is especially risky. Look out for the following warning signs, and if you have any doubts, slow down or stop and cool off.
* Nausea or vomiting. These symptoms can occur before true heatstroke, as running makes digestion harder. * Weakness. An unusual muscular weakness could be due to low blood sugar, but elevated core temperature also creates weakness. * Headache. This can also be caused by dehydration, or low blood sugar. Having had headaches from each of the three causes, I have found the type of headache is different. My limited experience is that a headache cased by heat is particularly painful and intense. * Dizziness or confusion. This is a serious symptom that suggests either extremely low blood sugar or heatstroke.
* Flushed/Hot Skin. I've found that an early warning sign is the feeling that my skin is burning, especially my face.
* Panting. Another symptom I've found of overheating is that my [[Breathing]] becomes labored beyond what is reasonable for the exercise intensity. * Core Temperature. The only sure test is to check your core temperature using something like an in-ear thermometer. Using a mouth thermometer may not be accurate if you've been [[Breathing]] hard.
If you have any doubts, stop and check your temperature. Avoid [[High Intensity Interval Training]] in the heat; the intense work can spike your core temperature too high too quickly for you to recover. It's possible that a runner that suffers heat stroke may exhibit none, or only one of these warning signs.
=Tips for Running in the HeatUsing Ice=* Get used to running in the heat slowly. See [[Heat Acclimation Training]] for more details* Check the temperature and humidity before you run. Knowing what to expect Ice can help you adjust your pace. Remember that humidity has be a big impact on your ability to cool off.* Run in the cooler parts of the day. Early morning and later in the evening work well, late afternoon is often the worst. * Stay Hydrated. The entry on [[Practical Hydration]] covers hydration and electrolytes. Remember that electrolytes are as important as water for staying hydrated. [[Hyponatremia]] can kill!* Cold drinks can also huge help lower your body temperature, but don't drink too much without electrolytes (see above tip on hydration)* Wear white. It may not be your favorite color, but it is the coolest (see below).* [[Under Armor Heat Gear Top]] in white can keep you cooler than bare skin* Wear a (white) hat. In very hot, sunny humid conditions, a . I'legionaries cap' can help protect your neck and face. See [[Running Hats]] for more details. * Adjust your pace for the heat. See [[Impact of Heat on Marathon Performance]] for some guidelines. * Protect yourself from the UV. Either wear sunscreen, or cover up. Remember that skin cancer is a nasty way to die. * Wear [[Sunglasses]] with UV protection. They not only protect you from the sunlight, but also help prevent your eyes drying out. * Wearing d recommend trying a [[Jimbo Bandana]] works wonders and it can be used while running (as well as for [[Precooling]].* Pouring water over yourself can help slightly* Watch out for [[Blister Prevention|blisters]] as your feet are more likely to be wet than in cooler conditions. * Run in the shade of possible. * Plan ahead; carry more drink with you than you expect to need. * For speed work, prefer shorter intervals and be very cautious. * Take [[Walking Breaks]] to cool off if you are having problems* Watch out for the warning signs listed above. I find nausea is the first sign I have of overheating and headache is my first sign of dehydration. * Carry a cell phone. If you get it wrong, you can call for help. (This is true in many situations.)* Changing your running route so that you are doing several shorter loops or out-and-backs. You can then cache some drinks for each section rather than carrying enough for the whole run.* Ice bandanas can also be used around the wrists. (Jim P)* Ice put ice under the a hat. (Jim P)* If you are doing loops, keep a spare shirt in a cooler full of ice, and switch every loopthough this can be quite painful when the cold hits your scalp. (Jim P)* Even holding some ice in your hand, or holding a cold water bottle can help<ref name="Hsu-2005"/>.* Some antidepressant medications have been linked Pouring water over your head, neck and body is an alternative, but watch out for the shock of the temperature differential. It's important to heatstroke'''never use gel packs''', only frozen water! Gel packs start off too cold, causing frostbite and skin damage, then warm up too quickly. If you use ice, it will start off just below freezing and then maintain that temperature until it's melted.
=The effect of clothing color=
A study<ref name="ShkolnikTaylor1980"/> comparing clothing color in hot conditions (38C) and strong sun showed that black clothes result in 2.5x the gain heat from the sun compared with white clothes. Tan clothing of a military uniform gained 1.7x more than white clothes and just shorts (semi-nude) gained 2.2x more. Therefore, it's important to wear white clothes in hot sunny conditions.
<ref name="Tucker-2004"> R. Tucker, L. Rauch, YX. Harley, TD. Noakes, Impaired exercise performance in the heat is associated with an anticipatory reduction in skeletal muscle recruitment., Pflugers Arch, volume 448, issue 4, pages 422-30, Jul 2004, doi [http://dx.doi.org/10.1007/s00424-004-1267-4 10.1007/s00424-004-1267-4], PMID [http://www.ncbi.nlm.nih.gov/pubmed/15138825 15138825]</ref>
<ref name="Hsu-2005"> AR. Hsu, TA. Hagobian, KA. Jacobs, H. Attallah, AL. Friedlander, Effects of heat removal through the hand on metabolism and performance during cycling exercise in the heat., Can J Appl Physiol, volume 30, issue 1, pages 87-104, Feb 2005, PMID [http://www.ncbi.nlm.nih.gov/pubmed/15855685 15855685]</ref>
<ref name="Goulet2012">E. D. B. Goulet, Effect of exercise-induced dehydration on endurance performance: evaluating the impact of exercise protocols on outcomes using a meta-analytic procedure, British Journal of Sports Medicine, volume 47, issue 11, 2012, pages 679–686, ISSN [http://www.worldcat.org/issn/0306-3674 0306-3674], doi [http://dx.doi.org/10.1136/bjsports-2012-090958 10.1136/bjsports-2012-090958]</ref>
<ref name="Goulet2011">E. D. B. Goulet, Effect of exercise-induced dehydration on time-trial exercise performance: a meta-analysis, British Journal of Sports Medicine, volume 45, issue 14, 2011, pages 1149–1156, ISSN [http://www.worldcat.org/issn/0306-3674 0306-3674], doi [http://dx.doi.org/10.1136/bjsm.2010.077966 10.1136/bjsm.2010.077966]</ref>
</references>
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