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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.

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.

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 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"/>.

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' 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.

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:

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.

The following advice should be used as guidance for heat acclimation training. Please use caution and common sense.

* 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="Armstrong-1991"/>, but up to 75% of acclimation is reached after 5 days <ref name="Shapiro"/>.

* 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"/>

This 'heat suit' will allow for heat training even in quite cool conditions.

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This combination will prevent the majority of heat escaping your body.

[[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 [http://www.amazon.com/Thermasol-PRO-240-240-Cubic-ProSeries-SmartSteam/dp/B00133Y9HS 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.

For those who want to know more details about heat acclimation, here is a summary of the scientific data.

Heat acclimation will produce a number of benefits

* Younger runners do better in the heat than older runners but training can negate this<ref name="Armstrong-1991"/>

* Acclimation is faster in fitter athletes<ref name="Armstrong-1991"/>

* On return to a cool climate, acclimation lasts for about a week, then decays<ref name="Armstrong-1991"/>

* People who have always lived in hot climates are believed to have superior adaptation<ref name="Noakes"/>

* Running calculators

** [[Running Heat Model]]

* [[Running in the Heat]]

* [[Impact of Heat on Marathon Performance]]

<references>

<ref name="Armstrong-1991"> LE. Armstrong, CM. Maresh, The induction and decay of heat acclimatisation in trained athletes., Sports Med, volume 12, issue 5, pages 302-12, Nov 1991, PMID [http://www.ncbi.nlm.nih.gov/pubmed/1763248 1763248]</ref>

<ref name="postsauna"> GS. Scoon, WG. Hopkins, S. Mayhew, JD. Cotter, Effect of post-exercise sauna bathing on the endurance performance of competitive male runners., J Sci Med Sport, volume 10, issue 4, pages 259-62, Aug 2007, doi [http://dx.doi.org/10.1016/j.jsams.2006.06.009 10.1016/j.jsams.2006.06.009], PMID [http://www.ncbi.nlm.nih.gov/pubmed/16877041 16877041]</ref>

<ref name="performance"> S. Lorenzo, JR. Halliwill, MN. Sawka, CT. Minson, Heat acclimation improves exercise performance., J Appl Physiol (1985), volume 109, issue 4, pages 1140-7, Oct 2010, doi [http://dx.doi.org/10.1152/japplphysiol.00495.2010 10.1152/japplphysiol.00495.2010], PMID [http://www.ncbi.nlm.nih.gov/pubmed/20724560 20724560]</ref>

</references>