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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.]]
Running in the heat is much harder than running in cooler temperatures, reducing performance and creating serious health risks. Moderate exercise in mild temperatures, such as 60f/15c, will reduce performance, but the perception is likely to be fatigue rather than overheating. Without preparation More extreme exercise or temperatures can create the risk of heat illnesses which can be punishing dangerous. =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 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 dangerousthough 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"/> . The most important step However, it is not clear to realize that running 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 requires just as much care as running 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 extreme cold[http://en.wikipedia.org/wiki/Gamma-Aminobutyric_acid GABA]<ref name="Mündel-2008"/>. ==Hyperthermia - Heat can kill==Running in the heat can kill, as the bodies 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* # Being overweight, as fat can act as an insulator.* # Being untrained, as fitness gives some heat adaptation over the unfit, and also teaches the mind some of the danger signs of heat problems.* # Lack of heat acclimatization, which both as this acclimatization gives some protection from the heat and also teaches the mind to adjust the intensity based on heat. * # Thinking you can run faster than you can in the conditions. * # Having suffered from heat illness before.* # Ignoring warning signs (see below).==Staying Alive in the Heat - The Warning Signs==
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.
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.
* 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 can help you adjust your pace. Remember that humidity has a big impact on your ability to cool off.
* Ice under the hat. (Jim P)
* If you are doing loops, keep a spare shirt in a cooler full of ice, and switch every loop. (Jim P)
* Even holding some ice in your hand, or holding a cold water bottle can [http:help<ref name="Hsu-2005"//www.ncbi.nlm.nih.gov/pubmed/15855685 help]>.
* Some antidepressant medications have been linked to heatstroke.
* Running calculators
** [[Running Heat Model]]
* [[Heat Acclimation Training]]
* [[Impact of Heat on Marathon Performance]]
=References=
<references>
<ref name="Snow-1993"> RJ. Snow, MA. Febbraio, MF. Carey, M. Hargreaves, Heat stress increases ammonia accumulation during exercise in humans., Exp Physiol, volume 78, issue 6, pages 847-50, Nov 1993, PMID [http://www.ncbi.nlm.nih.gov/pubmed/8311952 8311952]</ref>
<ref name="Marino-2001"> FE. Marino, Z. Mbambo, E. Kortekaas, G. Wilson, MI. Lambert, TD. Noakes, SC. Dennis, Influence of ambient temperature on plasma ammonia and lactate accumulation during prolonged submaximal and self-paced running., Eur J Appl Physiol, volume 86, issue 1, pages 71-8, Nov 2001, PMID [http://www.ncbi.nlm.nih.gov/pubmed/11820326 11820326]</ref>
<ref name="Mündel-2008"> T. Mündel, Exercise heat stress and metabolism., Med Sport Sci, volume 53, pages 121-9, 2008, doi [http://dx.doi.org/10.1159/000151554 10.1159/000151554], PMID [http://www.ncbi.nlm.nih.gov/pubmed/19209003 19209003]</ref>
<ref name="Nybo-2008"> Nybo, Lars. "Hyperthermia and fatigue." Journal of Applied Physiology 104.3 (2008): 871-878.</ref>
<ref name="Tucker-2008"> R. Tucker, Thermoregulation, fatigue and exercise modality., Med Sport Sci, volume 53, pages 26-38, 2008, doi [http://dx.doi.org/10.1159/000151548 10.1159/000151548], PMID [http://www.ncbi.nlm.nih.gov/pubmed/19208997 19208997]</ref>
<ref name="Tucker2006">R. Tucker, The rate of heat storage mediates an anticipatory reduction in exercise intensity during cycling at a fixed rating of perceived exertion, The Journal of Physiology, volume 574, issue 3, 2006, pages 905–915, ISSN [http://www.worldcat.org/issn/0022-3751 0022-3751], doi [http://dx.doi.org/10.1113/jphysiol.2005.101733 10.1113/jphysiol.2005.101733]</ref>
<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"> {{Cite journal | last1 = Hsu | first1 = AR. | last2 = Hagobian | first2 = TA. | last3 = Jacobs | first3 = KA. | last4 = Attallah | first4 = H. | last5 = Friedlander | first5 = AL. | title = Effects of heat removal through the hand on metabolism and performance during cycling exercise in the heat. | journal = Can J Appl Physiol | volume = 30 | issue = 1 | pages = 87-104 | month = Feb | year = 2005 | doi = | PMID = 15855685 }}</ref>
</references>