Changes

Some notes on If you're travelling to higher altitude or using [[Altitude Training]] and to improve performance, it's worth understanding the science of how altitude effects athletes. The key takeaways are that acclimation takes about two weeks and most people will benefit from iron supplements, ideally starting weeks or months before altitude exposure. =The Effects of altitudeAltitude=

* Altitude is generally considered High altitude as 1500 to 3500m (5,000' to 11,500'), Very high altitude as 3500 to 5500m (11,500' to 18,000'), and Extreme altitude as above 5500m (18,000')<ref name="ParalikarParalikar2010"/>.* Rapid ascent from near sea level to above 2500m/8,000' can result in problems ranging from mild sickness to life-threatening Acute Mountain Sickness (AMS), but with gradual acclimation extreme altitudes can be tolerated<ref name="ParalikarParalikar2010"/>. * One "rule of thumb" is that above 3000m/10,000', you shouldn't sleep more than 300m/1,000' higher than the previous night<ref name="ParalikarParalikar2010"/>. * A key feature of acclimation to altitudes up to 5,000m/16,000' is an increase in breathing<ref name="West2006"/>. Other changes include an increase in heart rate, increase in blood pressure, increase in red blood cells, reduction in blood volume (increased urine output), increase in capillary density, and an increase in mitochondria and oxidative enzymes<ref name="Goldfarb-RumyantzevAlper2013"/>. However, the increase in capillary density might be at least partly due to a reduction in muscle fiber size<ref name="MizunoSavard2008"/>.* The human body adjusts to lower blood oxygen saturation in many ways. One adaption , and one key adaptation that is of interest to athletes is an increase in red blood cells, but the performance improvements from [[Altitude Training]] may come from other additional sources<ref name="Nonhematological"/><ref name="CounterpointGoreHopkins2005"/>. * The effects of altitude are non-linear. From sea level to Leadville (10,170 ft), your blood oxygen levels may drop 6% from 96% to 90%. Going up another 4,000 ft to Pike's Peak (14,110), blood oxygen levels may drop a further 8% to 82%. Running is harder at altitude as seen by the [[VO2max]] drop. At Leadville your [[VO2max]] may drop by ~15% (range 4-30%)* [[SpO2|SpO₂]] at altitude may be slightly misleading as the oxygen deliver to the muscles may be modified by O₂ dissociation curve shifts caused by changes in pH, PCO₂, and blood temperature<ref name="DempseyWagner1999"/>. However, [[SpO2|SpO₂]] is cheap and easy to monitor and should not be ignored. * There is great individual variability in the response to altitude<ref name="ChapmanStray-Gundersen1998"/>. Some studies have classified subjects as 'responders' and 'non-responders' due to the significance of this variability. This variability can change over time within an individual. I met someone in Tanzania who had been a porter on Kilimanjaro (19,334 ft) until he lost his ability to cope with the altitude.* Some variability may be due to differences in iron intake/availability. Low blood iron (serum ferritin < 20 ng/ml female, < 30 ng/ml male) may limit the body's ability to generate new red blood cells, which is part of the altitude adaptation. Studies in the USSR and CIS have shown genetic factors as well. * The effects of altitude are non-linear. From sea level to Leadville (10,170 ft), your blood oxygen levels drop 6% from 96% to 90%. Going up another 4,000 ft to Pike's Peak (14,110), blood oxygen levels drop a further 8% to 82%. * Running is harder at altitude as seen by the [[VO2max]] drop. At Leadville your [[VO2max]] will drop by ~15% (range 4-30%)* Athletes' performance may drop noticeably even at relatively low altitudes. At 1,900 ft, a 5 minute maximal exertion test was 6% (male) and 4% (female) lower than at sea level. * Athletes may suffer See below for more at altitude than sedentary people, and men more than womendetails. * Generally , 'live high, train low' seems to work better than 'live high, train high'. [[Intermittent Hypoxic Exposure]] may have additional benefits over other [[Altitude Training Approaches]].* Altitude acclimatization generally takes 1-time, with 2 weeksbeing a point of diminishing returns. This is based on a study of athletes traveling to 2340m/7,766' that showed a performance decrease of 26% on arrival, with they recovered by 6.0% after 7 days, another 5.7% after 14 days, but only another 1.4 weeks as the recommended minimum to achieve benefits% after 21 days<ref name="Schuler-2007"/>. These findings seem broadly similar for those sleeping in an altitude tent (normobaric hypoxia) <ref name="Townsend-2002"/>.

* Altitude acclimatization generally seems to last several weeks.* It is a myth that if you can't arrive at altitude with time to acclimate, it's best to arrive near within a day of your event. This is based on the idea that performance at altitude declines for a period before improving. However, research shows that the reduction in performance occurs immediately and improves gradually over time<ref name="SchulerThomsen2007"/>. At moderate altitudes (1700m/5,600') performance was better after just 18 hours compared with 6 hours<ref name="Weston-2001"/>.=Nutrition and Altitude=There's good evidence that nutrition is important for altitude acclimation, at least as far as iron goes. For other nutrients, the evidence is a little less clear. ==Iron==For adaptation to altitude, probably the most critical nutrient is Iron. Low iron stores can result in reduced adaptation to altitude<ref name="Stray-GundersenAlexander1992"/> and altitude training will reduce the body's stores of iron<ref name="Roberts-1992"/>. It's been suggested that iron supplementation may need to be started some months prior to the needed altitude acclimation due to the time taken for iron store to accumulate<ref name="Askew1995"/>, and six weeks may be insufficient time<ref name="ChapmanStray-Gundersen1998"/>. One study found that in a group of 178 athletes, iron stores (serum ferritin) reduced by 33% without supplementation, reduced by 14% with 105mg/day of iron and increased by 37% with 210 mg/day of iron<ref name="ConnorGovus2015"/>. Further, the non-supplemented athletes only increased hemoglobin mass by 1.1%, those on 105mg/day by 3.3% and those on 210 mg/day by 4.0%. The supplements were started one week before, and during, altitude exposure. The supplements were not given randomly but based on serum ferritin status. Those with levels above 100 ug/L were not supplemented, those with 30-100 ug/L were given 105 mg/day and those below 30 ug/L were given 210 mg/day. This suggests that even those with good iron status may need supplementation. However, that's a lot of iron, considering the RDA for men is only 8 mg/day and women 18 mg/day, and the tolerable upper intake is only 45 mg/day. Taking more than four times the tolerable upper intake is a little worrying, and the study made no mention of reported side effects. The study used a prolonged release supplement that included 105 mg iron with 1,000 mg Vitamin C (which can increase absorption of Iron) in a product called "Ferro Grad C."==Antioxidants==There's some indications that "live high, train low" may increase the need for antioxidants<ref name="PialouxMounier2008"/>. However, while some studies suggest that antioxidant supplementation might be beneficial<ref name="Tauler-2006"/><ref name="Goldfarb-2007"/>, it seems the preponderance of evidence is that antioxidant supplements may hinder recovery and adaptation to training stress<ref name="Gomez-Cabrera-2008"/><ref name="Peternelj-2011"/><ref name="Teixeira-2009"/>. ==Carbohydrate==It's unclear if the macronutrient mix of carbohydrate/protein/fat should be different at altitude, as most claims of the need for a high carbohydrate diet at altitude are based on sea level studies rather than any change due to altitude<ref name="MichalczykCzuba2016"/>. ==Vitamin D==There's no evidence for Vitamin D supplementation at altitude specifically, though there is the suggestion<ref name="MichalczykCzuba2016"/> that Vitamin D benefits might be particularly valuable as it may act as a vasodilator<ref name="Li-2004"/><ref name="Wacker-2013"/>. There's also the possibility that longer you have term (months) exposure to extreme altitude could result in bone loss<ref name="TanakaMinowa1992"/>. =Hydration and Altitude=Within 90 minutes of exposure to acclimatehigher altitudes, urine output increases<ref name="HildebrandtOttenbacher2000"/><ref name="Swenson-1995"/>, resulting in the betterloss of water and sodium<ref name="SwensonDuncan1995"/>.The diuretic effects of low pressure at altitude may be exacerbated by the temperature, as cold conditions can result in "cold diuresis"<ref name="ssScott-2004"/><ref name="crowtherHynynenIlmarinen1993"/>. One study suggests that hydration could exacerbate performance problems at altitude, but the study was short term (1 hour) and used dehydration that was not related to the altitude<ref name="CastellaniMuza2010"/>* . While there is a net loss of water as a response to altitude, it's unclear if increased fluid intake would help or hinder performance. There is an argument that this loss of fluid is an important adaptation to altitude that concentrates the blood and reduces the demand on the heart<ref name="Grover-1986"/>. There is some evidence that increased hydration does not increase the blood volume and may exacerbate fluid retention<ref name="Bärtsch-1991"/>. (Fluid retention is the build up of fluid between or inside the cells rather than in the blood.) There is further risk of [[Hyponatremia]] with excessive drinking, so caution is needed, and the advice to suggest "drink to thirst" would seem to remain valid. (Note that humans can adapt while people with kidney problems may be able to tolerate short durations at modest altitudes, the risks are unclear<ref name="LuksJohnson2008"/>.)=Assessing Altitude Impact=The Lake Louise Scoring System (LLSS) is used to assess the severity of AMS (Acute Mountain Sickness, or altitude sickness). The 2018 version of the LLSS scores headache, Gastrointestinal symptoms, fatigue, dizziness, and functional disruption to provide an overall assessment of AMS severity<ref name="RoachHackett2018"/>. (Sleep disruption was removed as it does not appear to survive be well corelated with AMS<ref name="SchulzHall2014"/>.) However, analysis has shown that a single question is just as effective as the LLSS<ref name="MeierCollet2017"/>. This is the Clinical Functional Score, which asks "overall if you had any symptoms, how did they affect your activity?", with possible answers of # "Not at all."# "Symptoms present but did not force any change in activity or itinerary."# "My symptoms forced me to stop the ascent or to go down on my own power."# "I had to be evacuated to a lower altitude ."=Effects of hypoxia=Low levels of SpO₂ effect brain functioning as shown in the following table<ref name="Anesthesia"/>.{| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"! style="background-color: #F2F2F2;" |SpO₂! style="background-color: #F2F2F2;" |Description! style="background-color: #F2F2F2;" |Effect! style="background-color: #F2F2F2;" |Notes|-| style="background-color: #F9F9F9;" |100-80%| style="background-color: #F9F9F9;" |Mild Hypoxia| style="background-color: #F9F9F9;" |Normal brain functioning| style="background-color: #F9F9F9;" |This mild level of hypoxia does not affect the functioning of the brain, but some people can be sensitive enough to detect changes.|-| style="background-color: #F9F9F9;" |80-60%| style="background-color: #F9F9F9;" |Moderate Hypoxia| style="background-color: #F9F9F9;" |Decreasing brain function| style="background-color: #F9F9F9;" |Vision can be altered, including tunnel vision. Coordination is impaired in things like handwriting will deteriorate. Below 80% the skin may become blue (cyanosis). Mental functioning is impaired, sometimes creating euphoria or tranquility, including indifference to everything including pain. At this level some people become fixated on whatever they were doing when the hypoxia began, which can be dangerous. Memory and speech can also be impaired. There may be older treat visual hallucinations, feelings of depersonalization and even out of Everestbody experiences.|-| style="background-color: #F9F9F9;" |60-40%| style="background-color: #F9F9F9;" |Severe hypoxia| style="background-color: #F9F9F9;" |[[Muscle]] paralysis| style="background-color: #F9F9F9;" |Apparent unconsciousness.|-| style="background-color: #F9F9F9;" |<40%| style="background-color: #F9F9F9;" |Extreme hypoxia| style="background-color: #F9F9F9;" |Unconsciousness and eventually death| style="background-color: #F9F9F9;" ||}=Hypoxia and Altitude=The following table<ref name="EverestMehler1981"/>gives an idea of different [[SpO2|SpO₂]]levels at different altitudes. Intermittent Hypoxic Exposure can increase [[SpO2|SpO₂]]levels at a given altitude<ref name="HetzlerStickley2009"/>, which are specified in the table below for some altitudes. However, the actual [[SpO2|SpO₂]] value at a given altitude will vary on many factors, so use this as a rough guide only. {| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"! style="background-color: #F2F2F2;" |'''Altitude(feet)'''! style="background-color: #F2F2F2;" |'''Altitude(meters)'''! style="background-color: #F2F2F2;" |'''Air Pressure(mmHg)'''! style="background-color: #F2F2F2;" |'''Oxygen Pressure(mmHg)'''! style="background-color: #F2F2F2;" |''' % of sea level Oxygen'''! style="background-color: #F2F2F2;" |'''Equivalent O2 partialpressure at sea level'''! style="background-color: #F2F2F2;" |'''SpO₂Unconditioned'''! style="background-color: #F2F2F2;" |'''SpO₂Conditioned'''|-| style="background-color: #F9F9F9;" |0| style="background-color: #F9F9F9;" |0| style="background-color: #F9F9F9;" |760| style="background-color: #F9F9F9;" |159| style="background-color: #F9F9F9;" |100| style="background-color: #F9F9F9;" |20.9| style="background-color: #F9F9F9;" |98%| style="background-color: #F9F9F9;" ||-| style="background-color: #F9F9F9;" |5,000| style="background-color: #F9F9F9;" |1,524| style="background-color: #F9F9F9;" |639| style="background-color: #F9F9F9;" |134| style="background-color: #F9F9F9;" |84| style="background-color: #F9F9F9;" |17.6| style="background-color: #F9F9F9;" |95%| style="background-color: #F9F9F9;" ||-| style="background-color: #F9F9F9;" |7,500| style="background-color: #F9F9F9;" |2,286| style="background-color: #F9F9F9;" |584| style="background-color: #F9F9F9;" |122| style="background-color: #F9F9F9;" |77| style="background-color: #F9F9F9;" |16.1| style="background-color: #F9F9F9;" |93%| style="background-color: #F9F9F9;" ||-| style="background-color: #F9F9F9;" |9,000| style="background-color: #F9F9F9;" |2,740| style="background-color: #F9F9F9;" |554| style="background-color: #F9F9F9;" |116| style="background-color: #F9F9F9;" |73| style="background-color: #F9F9F9;" |15.3| style="background-color: #F9F9F9;" |90.3% (+/-3.4%)| style="background-color: #F9F9F9;" |93.8% (+/-2%)|-| style="background-color: #F9F9F9;" |10,000| style="background-color: #F9F9F9;" |3,048| style="background-color: #F9F9F9;" |534| style="background-color: #F9F9F9;" |112| style="background-color: #F9F9F9;" |70| style="background-color: #F9F9F9;" |14.6| style="background-color: #F9F9F9;" |89%| style="background-color: #F9F9F9;" ||-| style="background-color: #F9F9F9;" |11,000| style="background-color: #F9F9F9;" |3,360| style="background-color: #F9F9F9;" |514| style="background-color: #F9F9F9;" |107| style="background-color: #F9F9F9;" |68| style="background-color: #F9F9F9;" |14.2| style="background-color: #F9F9F9;" |86.4 % (+/- 4.8%)| style="background-color: #F9F9F9;" |90.2% (+/-2.7%)|-| style="background-color: #F9F9F9;" |12,500| style="background-color: #F9F9F9;" |3,810| style="background-color: #F9F9F9;" |487| style="background-color: #F9F9F9;" |102| style="background-color: #F9F9F9;" |64| style="background-color: #F9F9F9;" |13.4| style="background-color: #F9F9F9;" |87%| style="background-color: #F9F9F9;" ||-| style="background-color: #F9F9F9;" |14,000| style="background-color: #F9F9F9;" |4,267| style="background-color: #F9F9F9;" |460| style="background-color: #F9F9F9;" |96| style="background-color: #F9F9F9;" |61| style="background-color: #F9F9F9;" |12.7| style="background-color: #F9F9F9;" |83%| style="background-color: #F9F9F9;" ||-| style="background-color: #F9F9F9;" |15,000| style="background-color: #F9F9F9;" |4,570| style="background-color: #F9F9F9;" |443| style="background-color: #F9F9F9;" |93| style="background-color: #F9F9F9;" |58| style="background-color: #F9F9F9;" |12.1| style="background-color: #F9F9F9;" |81.7% (+/-6%)| style="background-color: #F9F9F9;" |89.1% (+/-3%)|-| style="background-color: #F9F9F9;" |16,500| style="background-color: #F9F9F9;" |5,029| style="background-color: #F9F9F9;" |418| style="background-color: #F9F9F9;" |87| style="background-color: #F9F9F9;" |55| style="background-color: #F9F9F9;" |11.5| style="background-color: #F9F9F9;" |77%| style="background-color: #F9F9F9;" ||-| style="background-color: #F9F9F9;" |18,000| style="background-color: #F9F9F9;" |5,490| style="background-color: #F9F9F9;" |395| style="background-color: #F9F9F9;" |83| style="background-color: #F9F9F9;" |52| style="background-color: #F9F9F9;" |10.9| style="background-color: #F9F9F9;" || style="background-color: #F9F9F9;" |84.9% (+/-4%)|-| style="background-color: #F9F9F9;" |20,000| style="background-color: #F9F9F9;" |6,096| style="background-color: #F9F9F9;" |365| style="background-color: #F9F9F9;" |76| style="background-color: #F9F9F9;" |48| style="background-color: #F9F9F9;" |10.0| style="background-color: #F9F9F9;" |65%| style="background-color: #F9F9F9;" ||-| style="background-color: #F9F9F9;" |21,000| style="background-color: #F9F9F9;" |6,400| style="background-color: #F9F9F9;" |351| style="background-color: #F9F9F9;" |73| style="background-color: #F9F9F9;" |46| style="background-color: #F9F9F9;" |9.6| style="background-color: #F9F9F9;" || style="background-color: #F9F9F9;" |79.2% (+/-6%)|-| style="background-color: #F9F9F9;" |25,000| style="background-color: #F9F9F9;" |7,620| style="background-color: #F9F9F9;" |299| style="background-color: #F9F9F9;" |62| style="background-color: #F9F9F9;" |39| style="background-color: #F9F9F9;" |8.2| style="background-color: #F9F9F9;" |<60%| style="background-color: #F9F9F9;" ||}=See Also==

 ==References==

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