It is fairly well accepted that extremes of temperature have a negative impact on physical and mental performance. What is perhaps surprising, if not entirely alarming, is just what qualifies as 'extreme'. In 2002, Pilcher and others conducted a meta-analysis of the various high-quality, scientific studies that had been undertaken on mental performance in extremes of temperature. They found that the worst cognitive performance occurred at anything below 10oC and anything above 32.2oC. In the U.K., we would tend to regard 10oC as mild for winter, and 32.2oC as a good day to telephone work sick and head down to Brighton. We would tend not to consider these temperatures as negatively affecting the mental faculties.
The extent to which temperature affects performance in a cognitive test depends very much on the nature of the task. Pilcher et al. (2002), reported that cold exposure below 18.3oC resulted in a substantial negative affect on reasoning, learning and memory tasks. Conversely, attentional, perceptual and mathematical tasks, along with reaction times, tend to decline more with heat than with cold.
Variations in the level of protective clothing, combined with sleep deprivation, windchill, and much lower ambient temperatures, would need to be assessed to give a fuller picture of the consequences of cold exposure. However, based on the findings mentioned above, navigation, discipline to eat, drink and rest, and self-awareness to recognise when it is time to wrap up a bit warmer, or else to climb into a sleeping bag or get a fire going, all require reasoning skills.
Learning and memory are, for example, key to knowing where items of equipment are kept, how to use them, and what sort of survival skills need to be employed in given situations. It is fair to say that the mental faculties would be ticking over at their slowest rate when racers are at their coldest, and when those faculties are needed the most.
A final, positive finding of the meta-analysis, was that subjects involved in long-term exposure seemed to manage better than those given a single, short blast of cold for an hour or two. This suggests a level of adaptation to the cold, whereby an individual's cognitive performance improves during the course of exposure. So, for those preparing to face the cold, it would appear that as we become more accustomed to the environment, so our ability to cope mentally should improve as well.
One issue that confounds many researchers of adaptation to the cold, particularly when investigating populations indigenous to higher latitudes, is that there really is not very much adaptation to investigate. This is mostly thanks to behavioural changes. In other words, if one ventures to sub-Arctic or Arctic populaces, what one invariably finds are people dressed up in very warm clothing.
Their cars are heated, their homes and offices are heated, and they are very experienced in how to protect themselves from the cold. If one takes a basking Brighton beach-dweller, clad in shorts, socks and sandals, and we drop them into the northern reaches of Scandinavia, even the most mentally sluggish of vocational truants will realise pretty swiftly that a warm refuge, pending an overhaul of their personal attire, is the order of the day.
In other words, there is little point in getting people standing naked in a cold room to see what happens, because it is so unlikely that anybody ever finds themselves naked and exposed for long in real life. Hence, science is unlikely to be discovering very much of real use. But then, how does a researcher decide what sort of level of protective clothing is appropriate, and what sort of weather conditions their subjects should be tested in? It makes investigation a fairly challenging task, if one desires that the findings of a study should actually be applied in some way.
Mäkinen (2007), found that circumpolar people did not demonstrate any sort of acclimatisation to cold, and that this was most probably due to how they wore adequate protective clothing, enjoyed high temperatures in their homes, and only permitted themselves the briefest of exposures to the outside world.
What Mäkinen did find was that cold affected cognitive performance, by increasing levels of distraction and vigilance. Whilst distraction is a negative consequence, increased vigilance could be either positive or negative, depending on the circumstances. Distraction and increased vigilance could be negative if it means a racer's pace is slowed whilst the gears of the mind are whirring away on anything else. Conversely, increased vigilance might be useful if directed at awareness of the land and signs of danger, such as avalanche risk, hazardous ground conditions, and an advancing moose.
One particularly interesting finding of Mäkinen's study, was that simple tasks suffered the most, whereas more complex tasks could actually improve in mild or moderate cold conditions. Mild and moderate cold are relative terms, of course, as they depend upon both external conditions and the effectiveness of clothing and so on. Whether or not setting up a bivvy or getting a fire going is simple or complex, is probably a matter of training and experience, amongst other things. Irritatingly, although Mäkinen found that there were some signs of habituation to the cold following repeated exposures, these did not have any positive effect on the signs of cognitive performance that were being measured.
In a study by Bishop et al. (2001), two men participating in a Greenland expedition were monitored and assessed for changes in physiological, psychological and behavioural data. Although behaviour was fairly consistent, due to the nature of the expedition, it was found that physiological and psychological functioning were very closely related, and followed the degree of challenge of the activity. Changes were evaluated both through levels of stress-related hormones and psychological assessments. The more they suffered physically, the more that caused them to suffer psychologically, and vice versa.
Ozaki et al. (2001), investigated the physiological and psychological effects of repeated cold exposure in night-shift workers. The researchers found that circadian variations permitted a marked decrease in core temperature at night compared with during the day. The circadian rhythms are normally responsible for a rise in core temperature during the day and a fall at night, regardless of levels of physical activity. Put another way, a set amount of physical activity during the night will induce a core temperature rise that is much lower than it would be for the same amount of activity during the day (Ozaki et al., 2001).
Conversely, the investigators reported that skin temperature was actually higher during the night, despite a cooler core temperature, and suggested that this may have been due to circulatory (thermoregulatory) inefficiencies. It was also noted that manual performance decreased at night, and that this must have reflected an overall cooling of the body. The main conclusion of the study was that night workers are more susceptible to hypothermia when exposed to cold at night, than day workers going about their duties in the day, even for the same environmental temperatures. This is predominantly due to the natural variations in circadian rhythms (Ozaki et al., 2001).
This finding also has direct relevance to endurance athletes that are racing during the night, as they will be more susceptible to the cold then, even if maintaining the same exercise intensity as during the day. However, it is most likely that exercise intensity will actually decrease at night, when the core temperature is already predisposed to being lower, and when in fact environmental temperatures will also be lower than during the day. Thus, a number of factors converge to increase the risk of exercising in the cold at night.
A study by Cheuvront et al. (2005), found that hypohydration (i.e. dehydration) affected cycle performance in temperate, but not cold environments. These investigators found no direct effect of cold on submaximal or maximal exercise tests, in difference to the findings of the study by Patton et al. (1984). However, in the study by Cheuvront et al. (2005), subjects were only exposed to the cold for one hour, as opposed to the thirty hours in the other study.
Further, some subjects suggested that they may have curtailed exercise in the cold due to motivational factors, thus making it difficult to ascertain a difference between euhydrated (normally hydrated) and hypohydrated (less than normally hydrated) states. One physiological possibility for why hypohydration affected performance in temperate but not cold environments relates to circulatory changes associated with cold exposure.
Readers of The Jungle Marathon may recall that, as a result of hypohydration, there is a decrease in the blood's plasma volume, which means that the heart must beat faster to shift the remaining blood around the body. This means that for a given exercise workload the heart rate is higher (or for a given heart rate the workload is lower), and overall an individual reaches exhaustion sooner due to that hypohydrated state.
In the cold the body does tend to reduce its blood volume, to keep blood centralised to the core and away from the periphery where it would be cooled by circulating close to the outside air. However, it would seem that if hypohydration is induced, there is still sufficient blood moving around the core to preserve stroke volume (the amount of blood pumped by the heart in each beat) and therefore heart rate is not affected.
A study by Kenefick et al. (2004), found that subjects exposed to the cold, whether euhydrated or hypohydrated, were less thirsty in either condition compared to when in a temperate environment. Importantly, despite increasing osmolarity of the blood in the hypohydrated state, thirst mechanisms were only effective in the temperate conditions, suggesting that in the cold the body's normal mechanisms to correct hyperosmolarity were impaired.
The kidneys are responsible for maintaining blood volume and osmolarity. If volume is too low, or osmolarity too high, then less water is excreted in urine, causing the urine to be more concentrated as the body still has to eliminate waste products. This occurs partly due to antidiuretic hormone (ADH), and as its levels rise, so the kidneys return more water to the blood. Kenefick et al. (2004), reported that levels of this hormone were not increased due to rising osmolarity as they would be in temperate conditions.
Thus, not only is the body less thirsty when exercising in the cold, compared with temperate conditions, but the internal mechanisms for maintaining blood homeostasis are inhibited as well. Whilst a single study can seldom be used to infer real-life consequences of similar conditions in the field, this certainly warrants further investigation. Kenefick's study involved exposure to the cold for a total of two and a half hours, so it is difficult to know what might occur following several hours, or even days, of continued exposure.
What we can take, however, is that exercise performance is likely to be reduced following several hours of exposure to the cold, and individuals are less likely to be aware of increasing hypohydration. Furthermore, it is possible that the body is less likely to correct hyperosmolarity, meaning that a more conscious control of electrolyte balance is vitally important.
If an individual is urinating frequently, and that urine is clear, then this would normally be a good indication of being euhydrated. However, in the cold it is possible that blood electrolyte levels might actually be going awry, despite typical indications that all is well. Because of this, it might be preferable to limit electrolyte intake to less than would be consumed in warmer climates. This conclusion, however, is tenuous and the matter requires further investigation.
It may be that electrolytes contained in foods are sufficient to maintain adequate levels, provided the individual is consuming sufficient quantities of water. The correct balance of water and electrolytes required for optimal hydration and health will no doubt be affected by the intensity of activity, the duration of exposure to the cold, and general dietary electrolyte intakes.
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