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Health and performance challenges during sports training and competition in cold weather

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  • United States Army Research Institute of Environmental Medicine

Abstract and Figures

Olympic athletes compete and train in diverse cold-weather environments, generally without adverse effects. However, the nature of some sports may increase the risk of cold injuries. This paper provides guidance to enable competition organisers and officials, coaches and athletes to avoid cold-weather injuries. This paper will (1) define potential cold-weather injuries during training and competition and (2) provide risk management guidance to mitigate susceptibility to cold-weather injuries.
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Health and performance challenges during sports
training and competition in cold weather
John William Castellani,
1
Andrew John Young
2
1
Thermal and Mountain
Medicine Division, US Army
Research Institute of
Environmental Medicine, Natick,
Massachusetts, USA
2
Military Nutrition Division, US
Army Research Institute of
Environmental Medicine, Natick,
Massachusetts, USA
Correspondence to
Dr Andrew John Young, Military
Nutrition Division, US Army
Research Institute of
Environmental Medicine,
42 Kansas Street, Natick,
MA 01760-5007, USA;
andrew.j.young@us.army.mil
Accepted 6 July 2012
ABSTRACT
Olympic athletes compete and train in diverse cold-
weather environments, generally without adverse effects.
However, the nature of some sports may increase the
risk of cold injuries. This paper provides guidance to
enable competition organisers and ofcials, coaches and
athletes to avoid cold-weather injuries. This paper will (1)
dene potential cold-weather injuries during training and
competition and (2) provide risk management guidance
to mitigate susceptibility to cold-weather injuries.
INTRODUCTION
Cold weather can create a risk of injury, but people
generally tolerate outdoor activities and cold expos-
ure without adverse effects. Tolerance largely
reects the protective advantages provided by
modern technology, since human physiological
responses defending body-temperature homeostasis
during cold exposure are less effective than during
heat exposure. For the most part, humans rely on
avoidance of cold to mitigate cold injury risk, by
either wearing protective clothing or taking shelter.
For elite athletes, however, the nature of the compe-
tition limits their ability to avoid cold exposure.
Athletes will, nevertheless, tolerate even severe cold
in pursuit of athletic success. Therefore, ofcials,
organisers and coaches must ensure that the envir-
onmental conditions during competition and train-
ing do not endanger the health of athletes. This
short article will review factors inuencing cold
injury risk, cold injury prevention strategies and
performance for athletes competing and training for
Olympic sporting events.
COLD INJURIES
When heat losses exceed heat production, body
heat content decreases and peripheral and core
temperatures decline. If unchecked, declining body
temperatures lead to cold injuries. There are two
major types of cold injuries: (1) hypothermia and
(2) peripheral tissue injuries.
With whole-body cooling, hypothermia is clinic-
ally dened by a core temperature below 35°C. Initial
symptoms include shivering, apathy and social with-
drawal. As core temperature continues falling below
35°C, confusion, sleepiness or slurred speech occur.
At core temperatures below 31°C, there may be
changes in cardiac rhythms. Mild hypothermia (core
temperature=3335°C) may be effectively treated
with simple rewarming (eg, warm shelter, blankets,
clothing, exercise and warm drinks), but more severe
hypothermia requires clinical treatment.
Peripheral cold injuries can be divided into freez-
ing and non-freezing injuries. However, non-
freezing or cold-wet injuries are not typically a
concern for athletes, because these injuries typically
require at least 12 h of skin exposure to cold-wet
(10°C) conditions. On the other hand, freezing
injuries, or frostbite, are a potential threat. Frostbite
occurs when tissue temperatures fall below 0°C.
Frostbite is most common in exposed skin (nose,
ears, cheeks and exposed wrists), but can occur in
clothed hands and feet. Instantaneous frostbite can
occur when skin contacts highly conductive cold
objects such as metal, which cause rapid heat loss.
The most common initial symptom of frostbite
is numbness. During re-warming of frostbitten
tissues, pain is signicant and re-warming should
be clinically supervised for all but the most minor
injuries.
Individual factors modifying responses to cold
and risk of injury
Laboratory studies suggest that physiological
responses for maintaining normal body tempera-
ture during cold exposure vary among individuals,
and that anthropometric, sex, tness and acclima-
tisation differences contribute to that variability.
1
For example, convective heat transfer at the skin
surface is the principal heat loss vector in
cold-exposed humans;
2
therefore, large individuals
lose more body heat in the cold than smaller indi-
viduals due to their larger body surface area.
However, this effect is somewhat mitigated since a
large body mass favours maintenance of a constant
temperature by virtue of a greater heat content
compared with a small body mass.
3
Additionally,
while all body tissues provide insulation, adipose
tissues thermal resistivity is greatest, so indivi-
duals with more adipose tissue experience smaller
body temperature changes and shiver less during
cold exposure than lean individuals.
3
Sex differ-
ences in heat ux and thermal balance during cold
exposure appear entirely attributable to anthropo-
metric differences between men and women, and
there is no denitive evidence of signicant sex dif-
ferences in thermoregulatory responses to cold.
Cross-sectional and longitudinal studies suggest
that physical training and/or high tness levels
confer little or no thermoregulatory advantages
during cold exposure,
3
with the exception that
tter individuals can sustain physical activity and
high rates of metabolic heat production longer
than less t individuals. Finally, cold acclimatisa-
tion has been shown to produce adjustments in
human thermoregulatory responses, but in con-
trast to heat acclimatisation, thermoregulatory
adjustments associated with cold acclimatisation
are relatively small, slower to develop and provide
little practical advantage for defending body tem-
perature and preventing environmental injury.
3
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Clothing probably represents the most important modiable
factor inuencing the magnitude of physiological strain and
environmental injury risk experienced by athletes during cold
exposure. Detailed consideration of biophysics and heat-
transfer properties of cold-weather athletic clothing is consid-
ered elsewhere.
4
Insulation provided by cold-weather clothing
adds to insulation provided by body fat and other tissues, so
that clothing requirements vary among individuals, and team
uniform policies should allow for individual adjustments. In
the simplest analysis, the amount of clothing insulation
required to maintain comfort and prevent excessive body heat
loss during cold-weather activity is determined by the thermal
gradient for heat loss (a function of ambient temperature and
wind), and rate of exercise thermogenesis (a function of exer-
cise intensity). Decreasing ambient temperature and increasing
wind necessitate increasing clothing insulation to prevent
excessive body heat loss, while increasing exercise intensity
and metabolic rates reduce the insulation required to protect
against a fall in body heat. During sports in which exercise
intensity is very high, metabolic heat production can be suf-
cient to prevent a fall in body temperature without the need
for heavy clothing, even when air temperature is extremely
low. On the other hand, athletes dressed appropriately to
achieve thermal balance during cold weather events may be
inadequately protected before starting, or after completing the
event, so additional clothing may be required at the sites of
warm-up and cool-down. Finally, if clothing becomes wet
from rain or sweating, insulation may be degraded and evap-
orative heat loss increased, further compromising protection of
body heat content.
EXERCISE IN THE COLD
The most important effects of exercise, at least in terms of how
cold exposure affects athletes, are the increases in thermogenesis
and peripheral blood ow (skin and muscles). The former tends
to balance increased heat loss in cold environments, while the
latter exacerbates heat loss by enhancing convective heat transfer
from the central core to peripheral shell. The thermogenic
response during exercise is usually sufcient to match or exceed
heat loss when exercise is performed in air.
2
In contrast during
swimming, the greater convective heat transfer coefcient of
water compared with air, produces rates of heat loss so great
that metabolic heat production during even intense exercise can
be insufcient to maintain thermal balance.
2
A noted physiologist, Dave Bass, once observed, man in the
cold is not necessarily a cold man. Whether cold exposure
inuences physiological responses and strain during exercise
depends on whether clothing insulation and exercise thermo-
genesis are sufcient to balance the rate of body heat loss to
the ambient environment. If so, core and skin temperatures
will remain elevated such that peripheral vasoconstriction and
shivering do not develop, and physiological strain and
responses will be the same as in temperate conditions.
However, during exercise at intensities too low for metabolic
heat production to balance heat loss and prevent shivering,
oxygen uptake during exercise will be higher than in warm
conditions due to the added metabolic requirements of the shi-
vering muscles.
3
Strenuous physical training can lead to exertional fatigue,
which can be severe in overtraining when strenuous exercise
and high levels of energy expenditure are sustained for long
periods. In such a state, people have difculty maintaining suf-
ciently high energy intake to maintain body energy stores,
and muscle and fat loss ensues. Sleep can also be disrupted by
intense training. Fatigue due to exertion, sleep restriction and
underfeeding impair an individuals ability to maintain thermal
balance in the cold,
5
and an anecdotal association between exer-
tional fatigue and susceptibility to hypothermia has also been
reported.
6
One explanation proposed is that with fatigue, the
exercise intensity and rate of metabolic heat production that
can be sustained declines, and core temperature can no longer
be defended during cold exposure. When underfeeding is a
factor, hypoglycaemia and/or muscle glycogen depletion could
develop. Acute hypoglycaemia impairs shivering through a
central nervous system effect,
78
and decreased peripheral carbo-
hydrate stores contribute to an inability to sustain exercise or
shivering, thus constraining thermogenesis during cold expos-
ure.
9
Studies also indicate that shivering and peripheral vaso-
constriction responses to cold may be directly affected, that is,
impaired, following strenuous exercise, repeated or prolonged
cold exposure, or both in combination.
1013
Whatever the
mechanism, fatigue, either acute or chronic, compromises the
ability to maintain thermal balance in the cold.
COLD INJURY PREVENTION DURING SPORTS
COMPETITION AND TRAINING
Risk management
Successful management of cold stress requires athletes, coaches
and competition ofcials to appreciate the nature of health
hazards associated with exercising in cold environments, and
employ suitable countermeasures to minimise the risk of hypo-
thermia and frostbite. With proper surveillance and oversight,
athletes can compete and train safely in most cold weather
environments, and there is usually no need to cancel events.
Formal risk management processes have been established to
identify potential hazards, contributing factors and effective
controls and counter measures for employment before/during/
after training and competition to prevent cold injuries to
athletes.
14
Risk management begins by identifying the hazard. The key
determinants of the risk of cold injury are the environmental
conditions to which the individual is exposed, specically
ambient temperature, wind speed, rain or snow fall rate.
Obviously, for athletes competing in or training in temperate or
warm environments (indoors or outdoors), the risk of cold
injury is nil. Thus, the sports in which cold injury constitutes a
real hazard are those competed outdoors during the Winter
Olympic Games, that is, Alpine and Nordic skiing, bobsledding,
luging, skeleton and snowboarding events. Additionally, long-
distance open-water swimming can be a cold injury hazard,
since immersion in even moderately cool water can potentially
constitute a signicant challenge to defending against excessive
body cooling. The rst step in assessing the risk of cold injury
during competition or training for these events is documenting
environmental conditions to which the athletes are exposed.
Archival weather reports obtained from various public sources
indicate that typical competition air temperatures for the
at-riskevents during the Vancouver, Turin, Salt Lake City and
Nagano Winter Olympic games ranged from 5 to 8 °C,
whereas somewhat more extreme low temperatures were
recorded during the Lillehammer (19 °C) and Calgary (15 °
C) games. However, those measurements were not necessarily
recorded near the event venue, or during the conduct of the
events, and there appears to be no ofcial, comprehensive
archive of weather data from previous Olympic winter events.
Rapidly changing weather conditions are common to regions
where Alpine and Nordic sports are competed, so it cannot be
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assumed that the weather measured at a site distant from the
competition accurately represents exposure conditions for com-
petitors, nor can it be assumed that conditions will remain con-
stant throughout the competition. Therefore, a system for
continuously measuring, recording and disseminating reliable,
real-time weather data at Olympic venues throughout competi-
tion should be implemented.
Figure 1 illustrates the factors that positively or negatively
modulate cold injury risk for an individual athlete during com-
petition or training. The sport-specic features inuencing risk
of cold injury to participants in at-riskOlympic events are
listed in table 1. As described earlier, whether hypothermia or
frostbite can occur during competition or training for these
events will depend on the degree to which these factors interact
to inuence body heat content, and associated changes in body
temperatures.
Frostbite prevention
Wind exacerbates convective heat loss
15
and reduces clothing
insulation. The Wind Chill Temperature Index (WCTI; gure 2)
integrates wind speed and air temperature to provide an esti-
mate of the cooling power of the environment.
16 17
The WCTI
standardises the cooling power of the environment to an
equivalent air temperature for calm conditions. More precisely,
the WCTI quanties the relative risk of frostbite (compared
with skin cooling rate in still air) and predicts times to freezing
of exposed facial skin.
18
It should be noted, however, that one
of the underlying assumptions inherent to the WCTI is that
the individual is sedentary, so WCTI overestimates frostbite
risk and underestimates time to skin freezing for individuals
exercising strenuously.
While wind facilitates heat exchange between the body and
environment, an exposed object (body) cannot cool below
ambient temperature. Thus, frostbite cannot occur when air
temperature is above 0°C. On the other hand, wind speeds
obtained from weather reports do not take into account
man-made wind. As shown in table 1, during Alpine and
Nordic skiing, snowboarding and sledding, participants move
(22100 km/h), thereby creating wind across the body at that
same rate, so the effective wind chill temperature for the
moving competitor would be lower, and risk of frostbite higher,
compared with non-moving spectators at that same venue.
Some Alpine skiing events can generate wind speeds of
100 km/h, but these events last less than 3 min, so the risk of
frostbite during those events still does not become high until
WCTI reaches 35°C. Overall, the risk of frostbite is less than
5% when the ambient temperature is above 15°C, but
increased safety surveillance is warranted when the WCTI
decreases below 27°C, as frostbite can occur in 30 min or
less.
14
Hypothermia prevention
In contrast to freezing injury, hypothermia can occur at any
ambient temperature that enables body heat losses to exceed
metabolic rate. Even exposures to temperatures well above
freezing can lead to hypothermia if metabolic rate is low, and
wet/windy conditions facilitate cooling relative to still, dry-air
conditions. Heat-loss prediction models
19
suggest that an
average-size person whose clothes are wet can maintain core
temperature above 35°C for at least 7 h if exercise is suf-
ciently intense enough to sustain metabolic rates of 600 W or
higher. Empirical data conrm that prediction, showing that
core temperature remained normal or above normal during
exercise at intensities above 60% VO
2max
(600700 W) in 4°C,
20 km/h wind speed conditions.
20
During all at-riskOlympic
events, metabolic rate is 600 W or higher, and exposure dura-
tions of most are less than 3 min, so there is little likelihood
of hypothermia during a competition. While some Nordic
skiing events do last as long as 2 h, metabolic rates during
these events are higher, further limiting the likelihood of
hypothermia, even if skin and clothing become wet. However,
during experimental exposures to 4°C, 20 km/h wind speed,
core temperature was observed to decline when exercise inten-
sity was low (eg, 35% VO
2max
) and clothing was wet.
61120
Therefore, the risk of hypothermia increases during precompe-
tition and postcompetition periods if competitors are not pro-
vided access to shelter or additional protective clothing.
Additionally, particularly during training, athletes who unex-
pectedly stop exercising (eg, injury) and/or become wet before
reaching shelter are at risk of hypothermia.
The greatest risk of hypothermia during Olympic events
may not be during the Winter Games. Participants in long-
distance, open-water swimming events might be at the great-
est risk of hypothermia of all Olympic athletes. Recognising
this hazard, the international swimming association does not
permit competition in water temperatures below 16°C, mea-
sured 1.4 m below water surface.
21
Modelling predictions
22 23
suggest that core temperature of a male athlete having typical
body composition of Olympic swimmers and swimming at a
sustained pace of 1.4 m s
1
in 16°C open water will fall to
35.7°C. Core temperature for a female Olympic swimmer
having a typical body composition and swimming at 1.3 m s
1
in 16°C water is actually predicted to increase by 0.5°C, and
is only predicted to decrease by 0.5°C in 12°C water tempera-
ture. However, if the pace maintained by these athletes slows
down as they fatigue, the swimmer is likely to reach clinical
levels of hypothermia.
Figure 1 Cold strain risk management process.
Table 1 Key characteristics of Olympic sports influencing risk of cold
injury to participants
Sport
Metabolic rate of
competitors (W),
(METS)
Event
duration
(min)
Airspeed
(km/h)
Alpine skiing, freestyle
skiing, ski jumping,
snowboarding
7001000 (711) 1.5322100
Sledding (Bobsled, Luge,
Skeleton)
600 (67) 132464
Nordic skiing, Biathalon,
Nordic combined
12501800 (1318) 24125 2227
10-K open water swimming 870 (910) 120
km/h, kilometres per hour; METS, metabolic equivalent; W, Watts.
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SUMMARY AND CONCLUSION
Cold injury is a concern during athletic training and competi-
tion. Our analysis indicates that the risk of cold injuries
during the Winter Olympics is probably quite small due to
the absence of extreme (20°C), the high metabolic rates ath-
letes produce during their events (>600 W), and the duration
of many of the events (3 min). Hypothermia is more likely
to occur during the 10 K open-water swim during the Summer
Olympics, if water temperatures approach 16°C. The risk of
cold injuries during training and non-Olympic competitions
could be higher than during Olympic competition.
Employment of formal risk management processes such as
those recommended by the American College of Sports
Medicine
14
can effectively mitigate those risks during competi-
tion and training.
Acknowledgements The views, opinions and/or ndings in this report are those
of the authors, and should not be construed as an ofcial Department of the Army
position, policy or decision, unless so designated by other ofcial documentation. This
work was supported by the US Army Medical Research and Materiel Command
(USAMRMC).
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.
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doi: 10.1136/bjsports-2012-091260
2012 46: 788-791Br J Sports Med
John William Castellani and Andrew John Young
weather
sports training and competition in cold
Health and performance challenges during
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The study aimed to develop and validate a convolutional neural network (CNN)‐based deep learning method for automatic diagnosis and graduation of skin frostbite. A dataset of 71 annotated images was used for the training, the validation, and the testing based on ResNet‐50 model. The performances were evaluated with the test set. The diagnosis and graduation performance of our approach was compared with two residents from burns department. The approach correctly identified all the frostbite of IV (18/18, 100%), but with respectively 1 mistake in the diagnosis of degree I (29/30, 96.67%), II (28/29, 96.55%) and III (37/38, 97.37%). The accuracy of the approach on the whole test set was 97.39% (112/115). The accuracy of the two residents were respectively 77.39% and 73.04%. Weighted Kappa of 0.583 indicates good reliability between the two residents (P = .445). Kendall's coefficient of concordance is 0.326 (P = .548), indicating differences in accuracy between the approach and the two residents. Our approach based on CNNs demonstrated an encouraging performance for the automatic diagnosis and graduation of skin frostbite, with higher accuracy and efficiency.
... It also occurs in military training (15,53,54). It is more common in rural, northern climates (13,16), in occupations involving high physical strain and extended cold exposure (14); and in leisure/sporting activities, such as mountaineering (17,18,55,56), cold climate hiking (57), use of all-terrain vehicles in the cold or of snowmobiles (16); and sports activities generating high wind speed, such as alpine skiing or sledding (58), or associated with prolonged stationary posture, such as kite skiing and hang gliding (59,60). A recent study concluded that the incidence of frostbite injuries in the Austrian Alps is low (56), mainly due to better awareness and clothing. ...
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Cold injury can result from exercising at low temperatures and can impair exercise performance or cause lifelong debility or death. This consensus statement provides up-to-date information on the pathogenesis, nature, impacts, prevention, and treatment of the most common cold injuries.
... Perhaps more importantly in the UK, wind chill can have a negative impact on performance in cooler conditions, reducing core body temperature and increasing the amount of anaerobic glycolysis in active muscles, leading to increased fatigue [107]. Furthermore, greater tness levels does not necessarily result in improved cold weather performance, this is more often dictated by body shape, size and sex [108]. ...
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Background: Despite increased awareness of climate change and urban air pollution, little research has been performed to examine the influence of meteorology and air quality on athletic performance of the general public and recreational exercisers. Anecdotal evidence of increased temperatures and wind speeds as well as higher relative humidity conditions resulting in reduced athletic performance has been presented in the past, whilst urban air pollution can have negative short- and long-term impacts on health. Furthermore, pollutants such as Ozone, Nitrogen Dioxide and Particulate Matter can cause respiratory and cardiovascular distress, which can be heightened during physical activity. Previous research has examined these impacts on marathon runners, or have been performed in laboratory settings. Instead, this paper focuses on the potential impacts on the general public. With the rise of parkrun events (timed 5 km runs) across the UK and worldwide concerns regarding public health in relation to both air quality and activity levels, the potential influence of air quality and meteorology on what is viewed as a ‘healthy’ activity has been investigated. A weekly dataset of parkrun participants at fifteen events, located in London UK, from 2011-2016 alongside local meteorological and air quality data has been analysed. Results[JH(G+ESLF1] : The biggest influencer on athletic performance is meteorology, particularly temperature and wind speed. Regression results between parkrun finishing times and temperature predominantly show positive relationships, supporting previous laboratory tests (p=0[JH(G+ESLF2] .01). Increased relative humidity also can be associated with slower finishing times but in several cases is not statistically significant. Higher wind speeds can also be related to slower times (p=<0.01) and in contrast to temperature and relative humidity, male participants are more influenced than female by this variable. Although air quality does influence athletic performance to an extent, the heterogeneity of pollutants within London and between parkrun events and monitoring sites makes this difficult to prove decisively. Conclusions: It has been determined that temperature and relative humidity can have the largest detrimental impact on parkrun performance, with ozone also being detrimental in some instances[JH(G+ESLF3] . The influence of other variables cannot be discounted however and it is recommended that modelling is performed to further determine the extent to which ‘at event’ meteorology and air quality has on performance. In the future, there results can be used to determine safe operating and exercise conditions for parkrun and other public athletics events. Key Points · Temperature and relative humidity have the largest detrimental impact on parkrun participants in the Greater London area. · Air quality impacts are less clear but it is shown that ozone, as an irritant to the cardiorespiratory system, can lead to slower times. · Modelling ‘at event’ air quality is recommended to improve data resolution and influence on participants.
... Perhaps more importantly in the UK, wind chill can have a negative impact on performance in cooler conditions, reducing core body temperature and increasing the amount of anaerobic glycolysis in active muscles, leading to increased fatigue [105]. Furthermore, greater tness levels does not necessarily result in improved cold weather performance, this is more often dictated by body shape, size and sex [106]. ...
Preprint
Full-text available
Background Despite increased awareness of climate change and urban air pollution, little research has been performed to examine the influence of meteorology and air quality on athletic performance of the general public and recreational exercisers. Anecdotal evidence of increased temperatures and wind speeds as well as higher relative humidity conditions resulting in reduced athletic performance has been presented in the past, whilst urban air pollution can have negative short- and long-term impacts on health. Furthermore, pollutants such as Ozone, Nitrogen Dioxide and Particulate Matter can cause respiratory and cardiovascular distress, which can be heightened during physical activity. Previous research has examined these impacts on marathon runners, or have been performed in laboratory settings. Instead, this paper focuses on the potential impacts on the general public. With the rise of parkrun events (timed 5 km runs) across the UK and worldwide concerns regarding public health in relation to both air quality and activity levels, the potential influence of air quality and meteorology on what is viewed as a ‘healthy’ activity has been investigated. A weekly dataset of parkrun participants at fifteen events, located in London UK, from 2011–2016 alongside local meteorological and air quality data has been analysed. Results The biggest influencer on athletic performance is meteorology, particularly temperature and wind speed. Regression results between parkrun finishing times and temperature predominantly show positive relationships, supporting previous laboratory tests. Increased relative humidity also causes slower finishing times but in several cases is not statistically significant. Higher wind speeds also result in slower times and in contrast to temperature and relative humidity, male participants are more influenced than female by this variable. Although air quality does influence athletic performance to an extent, the heterogeneity of pollutants within London and between parkrun events and monitoring sites makes this difficult to prove decisively. Conclusions It has been determined that temperature and relative humidity can have the largest detrimental impact on parkrun performance, with Ozone also having an impact. The influence of other variables cannot be discounted however and it is recommended that modelling is performed to further determine the extent to which ‘at event’ meteorology and air quality has on performance. In the future, there results can be used to determine safe operating and exercise conditions for parkrun and other public athletics events.
... ECSs can also cause severe injury to athletes during athletic training and competition. Analyses indicates that the risk of cold injuries in winter sports tends to increase in colder weather with a strong wind chill, especially for outdoor events in mountainous areas [14]. Outdoor games are also significantly affected by adverse weather events. ...
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Chapter
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In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.
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The sections in this article are:
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Participants in prolonged, physically demanding cold-weather activities are at risk for a condition called "thermoregulatory fatigue". During cold exposure, the increased gradient favoring body heat loss to the environment is opposed by physiological responses and clothing and behavioral strategies that conserve body heat stores to defend body temperature. The primary human physiological responses elicited by cold exposure are shivering and peripheral vasoconstriction. Shivering increases thermogenesis and replaces body heat losses, while peripheral vasoconstriction improves thermal insulation of the body and retards the rate of heat loss. A body of scientific literature supports the concept that prolonged and/or repeated cold exposure, fatigue induced by sustained physical exertion, or both together, can impair the shivering and vasoconstrictor responses to cold ("thermoregulatory fatigue"). The mechanisms accounting for this thermoregulatory impairment are not clear, but there is evidence to suggest that changes in central thermoregulatory control or peripheral sympathetic responsiveness to cold lead to thermoregulatory fatigue and increased susceptibility to hypothermia.
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In this paper a dynamic model of the human/ clothing/environment-system is developed. The human body (controlled system) is subdivided into six segments consisting of the head, trunk, arms, hands, legs and feet. Each segment is further divided into the core, muscle, fat, and skin layer. The afferent signal of the controlling system is composed of the weighted temperatures measured by thermal receptors at sites distributed in the body. The difference between this signal and its threshold activates the thermoregulatory actions: vasomotor changes, metabolic heat production and sweat production. The model considers the competition between skin and muscle blood flow during exercise in hot environments because of limited cardiac capacity, as well as cold induced vasodilatation. Additionally a combined model of heat and mass transfer from the skin through clothing to the environment is developed and incorporated into the thermoregulatory model. The human/clothing model can be used to investigate the interaction between the human body, clothing and environment. The model is validated by comparing the simulation with experimental results under different conditions: heat, cold, exercise, clothing and transient phases. It turns out that the simulation is compatible with the experimental results. We conclude that the model can be applied in a broad range of environmental conditions. Application of the model is easy via a user-friendly interface i.e. a WINDOWS-shell. Language: en
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The formula used in the U.S. and Canada to express the combined effect of wind and low temperature on how cold it feels was changed in November 2001. Many had felt that the old formula for equivalent temperature, derived in the 1960s from Siple and Passel's flawed but quite useful Wind Chill Index, unnecessarily exaggerated the severity of the weather. The new formula is based on a mathematical model of heat flow from the upwind side of a head-sized cylinder moving at walking speed into the wind. The paper details the assumptions that were made in generating the new wind chill charts. It also points out weaknesses in the concept of wind chill equivalent temperature, including its steady-state character and a seemingly paradoxical effect of the internal thermal resistance of the cylinder on comfort and equivalent temperature. Some improvements and alternatives are suggested.
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The objective of the present study was to define the risk and the time required to develop frostnip on the face during exposure to cold winds. Twelve subjects (6 males and 6 females) were exposed to sixteen 45 min tests where the wind intensity varied between 0, 16 and 32 km/h. The tests were conducted at 0, -10, -20, -30, -40 and 50 C (only 0 km/h wind was present at -50 C). During the tests, the subjects were dressed for thermal comfort, and rested seated while facing the wind with their bare face fully exposed to the cold wind. Each test was terminated when the elapsed time reached 45 min, or when frostnip developed. The results show that no frostnip was observed at 0 C and -10 C for any wind intensity. The frequency of frostnip development increases inversely with temperature, while the time to develop frostnip increases with temperature. At -20 C, 17 and 58% of the subjects developed frostnip for the 16 and 32 km/h wind conditions, while at 30 and -40 C, all the subjects developed frostnip at those conditions. For the no wind conditions, 0, 11, 22, and 60% of the subjects developed frostnip for the 20, -30, -40 and -50 C conditions, respectively. The time to develop frostnip decreased from 20 min at -20 C for the 16 and 32 km/h wind conditions to 14, 4, 2.5 and 1.5 min for the -30 C and 16 km/h, -30 C and 32 km/h, -40 C and 16 km/h, and -40 C and 32 km/h condition, respectively. It was concluded from these results that the risk of frostbite and times to develop frostbite estimated from Siple and Passel are based on conditions that are too severe and need revision to include more mild conditions. A new guideline based on the new Wind Chill Index is proposed to protect the general population against the development of freezing injuries, particularly on the face.
Chapter
The sections in this article are: Metabolic Adjustments to the Cold Critical Temperature Thermogenesis Below Critical Temperature Heat Transfer and Thermal Adjustments to the Cold Skin‐to‐Water Heat Transfer Core‐to‐Skin Heat Transfer Core‐to‐Core Heat Transfer Core‐to‐Environment Heat Transfer Thermal Balance in the Cold Thermal Balance by Analysis of Survival Data Thermal Balance Assessed by Thermal Models Stability of Skin and Core Temperatures Still Conditions vs. Voluntary Exertion