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Heat Acclimation Training

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[[File:2013 Badwater.jpg|right|thumb|500px|I've done quite a bit of [[Running in the Heat]], from North Carolina's brutal summers, to winning the [[2010 Keys 100]] or pacing Chris Moon at the [[2013 Pacing Badwater 135| Badwater 135]].]]Heat acclimation training can improve performance in hot and cold conditions. It also helps protect against heat injury and is particularly important when training for spring races. However, heat adaptation training can be dangerous, and care must be taken to avoid injury or death. ==Introduction==
Training for a spring race requires extra caution as you will have been training through the winter and be unprepared for warm conditions. While a spring race may be cool, there is also a risk of conditions that are warm enough (above 40f) to impair performance (see [Impact of Heat on Marathon Performance] for more details). Heat acclimation training, sometimes called heat adaptation training, can prepare you for these warmer conditions. This type of training is also valuable if you are traveling to a warmer climate for a race, or if you are training in the cool part of the day for a race in the warmer times. In addition, heat acclimation can improve cold weather performance. One study<ref name="performance"/> showed that heat acclimation improved performance in the cold by 6% and by 8% in heat.
==Background==Exercise becomes harder as the temperature rises, with 40 degrees Fahrenheit being close to optimal. Exercise in the heat causes blood vessels in the skin to expand to help with cooling. The demands of the extra blood for cooling creates added stress on the cardiovascular system<ref name="Caso"/>. The athlete’s athlete's body will also sweat to produce cooling; in dry conditions evaporation of sweat provides 98% of cooling and in humid conditions 80%<ref name="Caso"/>. The loss of fluids due to sweating can lead to dehydration that also impairs performance. The impact of dehydration is in addition to the impact of the heat<ref name="Caso"/>. ==Danger of Death==A dedicated athlete can push themselves hard enough to raise their core temperature to dangerous levels, leading to heatstroke, which can be fatal<ref name="Binkley"/>. Heatstroke can be the result of prolonged exercise in hot conditions, but it can also be the '''result of shorter periods of high intensity exercise, especially in the untrained or overweight'''. It is vitally important that heat acclimation training is started gradually. You must become aware of how your body is adjusting to the heat, and to learn the warning signs of elevated core temperatures. Training in heat suits (see below) is especially dangerous, as the heat will not escape even after you collapse! Generally, an athlete reaches ‘voluntary exhaustion’ 'voluntary exhaustion' when their core temperature reaches about 39c/102f<ref name="Nielsen"/>, so never push hard with heat acclimation. I would take it as a personal favor if you could avoid killing yourself. ==Symptoms of Heat Stroke==
If you have any of the following symptoms while performing heat acclimation training, you should stop and cool off. Taking your internal temperature, ideally with an in-ear thermometer will allow you to double check if this is heat stroke. Heat stroke is caused by an internal temperature of >40.6 °C (105.1 °F), is extremely dangerous and can be fatal. The following can be symptoms of heat stroke:
* [[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 caused by heat is particularly painful and intense. * Dizziness or confusion. This is a serious symptom that suggests either extremely low blood sugar or heatstroke.* Panting. My personal experience is that when my core temperature rises, I start to breathe more rapidly. The panting can occur at rest in a sauna, or during exercise where my breathing rate is far deeper and faster than would be typical for the exercise intensity. This panting may be a reflect that attempts to cool the body in the same way as a panting dog. I find this is the first warning of problems and a sign that I have to reduce the heat stress rapidly.
If you have any doubts, stop and check your temperature. Never do [[High Intensity Interval Training]] as part of heat acclimation; the intense work can spike your core temperature too high too quickly for you to recover.
==Practical Heat Training==
The following advice should be used as guidance for heat acclimation training. Please use caution and common sense.
* Like any new training routine, start off slowly and build up both duration and intensity over time. * Be Measure your core temperature, ideally with an in-ear infrared sensor<ref name="EricksonKirklin1993"/><ref name="DevrimKara2007"/><ref name="NimahBshesh2006"/>. I use a Braun ThermoScan and I've been pleased with it.* Beware a rapid rise in core temperature. Your temperature could continue to rise for a while after you stop exercising, which can be dangerous. * Aim for a core temperature of 38.5c/101.3f and do not let your core temperature go over 39.0c/102.2f. This is based on my review of heat adaptation studies shown below. * Your core temperature should rise over about 30 minutes to your target core temperature. * In addition to monitoring your core temperature, be aware of how you are feeling and avoid pushing too hard. * Build up to exercising at 50% [[VO2max]] or above<ref name="Armstron1991Armstrong-1991"/>. 50% of [[VO2max]] is about 70% of maximum [[Heart Rate]]<ref name="swain"/> or "very slow running"<ref name="brianmac"/>.
* Use gradually increasing periods from 30 to 100 minutes over 10 to 14 days<ref name="Shapiro"/>
* Acclimation is fully developed after 7 to 14 days<ref name="Armstron1991Armstrong-1991"/>, but up to 75% of acclimation is reached after 5 days <ref name="Shapiro"/>.* Reduce your training load to compensate for the added stress of the heat. The heat can make you far more tiered tired than you would expect.
* Consider alternating heat acclimation training and cooler training to preserve intensity<ref name="Noakes"/>
* Training in a warmer environment is ideal, but creating a microclimate (see Heat Suit below) by overdressing also works<ref name="Noakes"/>
* Exercise in heat produces better acclimation than passive heat<ref name="ismj"/>, but passive heat (sauna) following exercise can also be quite effective<ref name="postsauna"/>. * Maintain hydration levels, as dehydration may impair key adaptations, such as increased sweat rate<ref name="TraversNichols2020"/>.* Once gained, heat adaptation can be maintained for at least a month by training in the heat every five days<ref name="PryorPryor2019"/>. Without continued heat exposure, it's estimated that 2.5% of adaptation is lost each day<ref name="DaanenRacinais2017"/>.* Don't combine heat and altitude training as the altitude may impair heat adaptation<ref name="McCleaveSlattery2019"/>. =Fellrnr Heat Suit==This 'heat suit' will allow for heat training even in quite cool conditions. However, it <table style="margin: 0px 10%; border: 1px solid #aaa; border-left: 10px solid #a00000; background: #fbfbfb;"><tr><td class="mbox-image"> [[File:Ambox warning pn.svg|42px]]<td class="mbox-text"><div>This heat suit works by preventing the body cooling itself, so it increases the risk of heat stroke. If you overheat wearing this heat suit, you will may not cool off after you collapse. Please be careful taking this approach, and start off with very low intensity exercise. Build up the duration and intensity very gradually and monitor for warning signs. Please be careful, as I've had some close calls using this technique and it is dangerous. See "Symptoms of Heat Stroke" above. </div></table>The key to the Fellrnr Heat Suit comes from two waterproof layers. A traditional sweat suit uses a single waterproof layer to trap your sweat and preventing it from cooling your body. The problem with the single layer is that the sweat soaks through any clothing and reduces the insulation. In cooler conditions the sweat soaked clothes can become chilly even with the waterproof layer. The Fellrnr Heat Suit approach traps the sweat away from the insulation layer, preventing this cooling effect. The Fellrnr Heat Suit has the following layers over both your top and legs.{| class="wikitable" |- valign="top"|[[File:* HeatSuit1.JPG|none|thumb|x300px|A close fitting thermal layer near the skin. The purpose of this layer is to hold the sweat and keep your skin relatively comfortable. I wear a Halo hat to prevent the sweat getting in my eyes, plus a thin hat to prevent the waterproof hood sticking to my ears.]]* |[[File:HeatSuit2.JPG|none|thumb|x300px|A waterproof layer that traps the sweat in the first thermal layer.Ideally this should be a non-breathable waterproof layer.]]* |[[File:HeatSuit3.JPG|none|thumb|x300px|An insulation layer, such as fleece that prevents any heat escaping. Because it is trapped between the two waterproof layers, it never becomes wet. ]]* |[[File:HeatSuit4.JPG|none|thumb|x300px|A second waterproof or windproof layer that traps the body’s body's heat in the insulation layer. * In addition, wear hat, gloves and ideally a neck warmer or face mask. ]]|}This combination will prevent most of the majority of heat escaping your body. =Steam Shower=[[File:SteamShower.JPG|none|thumb|300px|My steam shower, with a nice mosaic and a bench to relax on.]]I have a steam shower which I also use for heat acclimation, and it's wonderful. We put in the [ Thermasol Smart Steam] system that was expensive, but well worth it. It provides rapid steam, with the initial steam after just a minute or so, and serious heat stress after about 5-10 minutes. If you turn it up, it will exceed your ability to cope quite quickly, or provide extended exposure at more moderate levels. =The Science of Heat Acclimation==
For those who want to know more details about heat acclimation, here is a summary of the scientific data.
==Core Temperature for Heat Acclimation==While most studies specified an ambient temperature and humidity, there are some that specified a target core temperature and time. This suggests that a core temperature of 38.5c/101.3f is a reasonable target and should be safe. You should keep your core temperature under 39.7c/103.4f and you should rapidly cool off if you hit that level. Your core temperature can continue to rise after you finish exercising, and if your core temperature goes too high you may be mentally impaired, so think ahead. * Target core temperature of 38.5c/101.3f for 90 minutes, with the target temperature reached over about 30 minutes<ref name="GarrettGoosens2009"/><ref name="GarrettCreasy2011"/><ref name="NealCorbett2016"/><ref name="PattersonStocks2004"/>.* Target core temperature of just over 39.0c/102.2f, for 2x 50 minutes with 10-minute recovery<ref name="KuennenGillum2011"/> or for 2 hours<ref name="KirbyConvertino1986"/>* Target core temperature of 38.5c/101.3f or 39.0/102.2f for 90 minutes <ref name="GibsonMee2015"/> (similar results.) * Passive heat exposure with core temperatures of 38.5c/101.3f to 39.0/102.2f for 2 hours<ref name="BeaudinWalsh2012"/>* One study explicitly set a core temperature limit of 39.7c/103.4f<ref name="GibsonTurner2015"/> but didn't give the rationale for that cut off. This is close to heat stroke temperatures, and it's not clear why the cutoff was chosen to be so high. * The diagnostic criteria for heat stroke is 40c/104f<ref name="Expert2016"/>/ Obviously this is a clear upper limit for core temperature. ==Changes with heat acclimation===Heat acclimation will produce a number of several benefits* Increased blood volume<ref name="NielsenHales1993"/>.* Sweating occurs at lower temperatures<ref name="Noakes"/>.* Sweat contains less electrolytes<ref name="Noakes2"/>.* Sweating is more profuse<ref name="Nielsen"/>.* Increased cardiac output in hot conditions<ref name="Nielsen"/>.* Reduced core temperature for given exercise time and intensity<ref name="Nielsen"/>.* The athlete becomes psychologically prepared for heat stress. <ref name="ismj"/>.* The ability to consume and absorb more fluids (anecdotal evidence only) .===Notes on Heat Acclimatization ===* Younger runners do better in the heat than older runners , but training can negate this<ref name="Armstron1991Armstrong-1991"/>* Acclimation is faster in fitter athletes<ref name="Armstron1991Armstrong-1991"/>* On return to a cool climate, acclimation lasts for about a week, then decays<ref name="Armstron1991Armstrong-1991"/>
* People who have always lived in hot climates are believed to have superior adaptation<ref name="Noakes"/>
* A sauna will produce similar heart rate and cardiac stress as 60-100w of exercise<ref name="KetelhutKetelhut2019"/>. My experience matches that estimate for heart rate, though my respiration tends to be much higher as my body attempts to pant to cool off. ==See Also==
* Running calculators
** [[Running Heat Model]]
* [[Running in the Heat]]
* [[Impact of Heat on Marathon Performance]]
 == references =References=
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