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Over the period 1980-2009, there were 58 documented hyperthermia deaths of American-style football players in the United States. This study examines the geography, timing, and meteorological conditions present during the onset of hyperthermia, using the most complete dataset available. Deaths are concentrated in the eastern quadrant of the United States and are most common during August. Over half the deaths occurred during morning practices when high humidity levels were common. The athletes were typically large (79% with a body mass index >30) and mostly (86%) played linemen positions. Meteorological conditions were atypically hot and humid by local standards on most days with fatalities. Further, all deaths occurred under conditions defined as high or extreme by the American College of Sports Medicine using the wet bulb globe temperature (WBGT), but under lower threat levels using the heat index (HI). Football-specific thresholds based on clothing (full football uniform, practice uniform, or shorts) were also examined. The thresholds matched well with data from athletes wearing practice uniforms but poorly for those in shorts only. Too few cases of athletes in full pads were available to draw any broad conclusions. We recommend that coaches carefully monitor players, particularly large linemen, early in the pre-season on days with wet bulb globe temperatures that are categorized as high or extreme. Also, as most of the deaths were among young athletes, longer acclimatization periods may be needed.
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A retrospective analysis of American football hyperthermia
deaths in the United States
Andrew J. Grundstein &Craig Ramseyer &Fang Zhao &
Jordan L. Pesses &Pete Akers &Aneela Qureshi &
Laura Becker &John A. Knox &Myron Petro
Received: 4 August 2010 / Revised: 22 November 2010 / Accepted: 22 November 2010
#ISB 2010
Abstract Over the period 19802009, there were 58
documented hyperthermia deaths of American-style foot-
ball players in the United States. This study examines the
geography, timing, and meteorological conditions present
during the onset of hyperthermia, using the most complete
dataset available. Deaths are concentrated in the eastern
quadrant of the United States and are most common during
August. Over half the deaths occurred during morning
practices when high humidity levels were common. The
athletes were typically large (79% with a body mass index
>30) and mostly (86%) played linemen positions. Meteo-
rological conditions were atypically hot and humid by local
standards on most days with fatalities. Further, all deaths
occurred under conditions defined as high or extreme by
the American College of Sports Medicine using the wet
bulb globe temperature (WBGT), but under lower threat
levels using the heat index (HI). Football-specific thresh-
olds based on clothing (full football uniform, practice
uniform, or shorts) were also examined. The thresholds
matched well with data from athletes wearing practice
uniforms but poorly for those in shorts only. Too few cases
of athletes in full pads were available to draw any broad
conclusions. We recommend that coaches carefully monitor
players, particularly large linemen, early in the pre-season
on days with wet bulb globe temperatures that are
categorized as high or extreme. Also, as most of the deaths
were among young athletes, longer acclimatization periods
may be needed.
Keywords American football .Hyperthermia .Climate .
United States
Over the last 50 years (19602009), there have been 123
documented cases of American-style football players in the
United States dying from heat-related illnesses (Mueller
and Colgate 2010), including 58 well-documented cases
from 19802009. Football players are particularly suscep-
tible to heat-related illnesses in part because of the timing
of pre-season practice, often in the late summer when
conditions are hot and humid. A climate study of optimal
practice times in Alabama found that there were no suitable
times for outdoor practices in full uniform in August
(Francis et al. 1991). Additionally, the level of clothing
football players wear may increase metabolic heat produc-
tion and inhibit cooling (e.g., Fox et al. 1966; Mathews et
al. 1969; Kulka and Kenney 2002; McCullough and
Kenney 2003; Brothers et al. 2004; Armstrong et al.
2010). A full football uniform, for example, may impede
evaporative heat loss by 6070% (Mathews et al. 1969).
Finally, football players tend to have physical character-
istics that may increase heat storage, such as greater muscle
mass, lower body surface area to body mass ratios, and
higher body fat percentages (Godek et al. 2004).
A variety of safety guidelines for practicing under
different environmental conditions have been established
by organizations such as Sports Medicine Australia, The
American College of Sports Medicine, and the American
Academy of Pediatrics (Armstrong et al. 1996; Binkley et
al. 2002; American Academy of Pediatrics, Committee on
Sports Medicine and Fitness 1991,2000; Sports Medicine
Australia 2010). These guidelines rely on a derived variable
A. J. Grundstein (*):C. Ramseyer :F. Zhao :J. L. Pesses :
P. Akers :A. Qureshi :L. Becker :J. A. Knox :M. Petro
Department of Geography, University of Georgia,
Room 204, 210 Field St,
Athens, GA 30602, USA
Int J Biometeorol
DOI 10.1007/s00484-010-0391-4
called the wet bulb globe temperature (WBGT; Yaglou and
Minard 1957) that integrates the influence of air tempera-
ture, humidity, and solar radiation. Depending on the
threshold, recommendations are made about the level of
risk and whether changes in how the practice is conducted
are needed. Cooper et al. (2006), however, noted that these
standards are generic and do not account for the particular
sport, the equipment worn, or fitness of the athlete.
Football-specific thresholds based on air temperature and
humidity were established for different levels of dress
including full pads, light pads, and shorts only by Kulka
and Kenney (2002). Using subjects that walked on a
treadmill wearing different types of clothing and under
different meteorological conditions, they identified levels of
uncompensable heat stress in which the body becomes
unable to maintain a thermal balance. A limitation of this
method is that it makes assumptions about the level of
activity and does not account for other meteorological
factors such as solar radiation or wind that may affect
exertional heat stress (Kulka and Kenney 2002). Coyle
(2003) expressed thresholds for uncompensable heat stress
for the different levels of dress in terms of WBGT using
empirical relationships between the black globe temperature
and dry bulb temperature.
Several studies have examined environmental conditions
and health outcomes in football players. Cooper et al.
(2006) investigated the use of the WBGT and safety
thresholds established by the American College of Sports
Medicine (ACSM) at five universities in the southeastern
United States. They noted that the highest risk of heat-
related illness was in the first few weeks of practice in
August. Most illnesses (97%) occurred under high-risk or
extreme-risk categories. The clothing-specific standards of
Kulka and Kenney (2002) were studied during football
training sessions. Godek et al. (2004) noted that in many
cases players in partial or full football uniforms were able
to train at levels that exceeded thresholds without any signs
of heat-related illnesses because periods of inactivity
allowed the athletes to cool and maintain a thermal balance.
In particular, the meteorological conditions during
football hyperthermia deaths have rarely been examined.
Only two studies have performed retrospective analyses
relating weather conditions to hyperthermia deaths in
football players. Fox et al. (1966) studied nine deaths from
1959 to 1962. They noted that all were interior linemen in
full football uniforms and most died during the first 2 days
of practice. Deaths occurred under a range of conditions
from higher temperatures and lower relative humidities to
lower temperatures and higher relative humidities. Kulka
and Kenney (2002) added data on three deaths in 2001 to
Fox et al.s study and placed these values in the context
of risk thresholds that accounted for level of clothing. They
found that all cases fell at or above the level of
uncompensable heat stress for exercise in a full football
Our study builds upon Fox et al. (1966) and utilizes the
largest available dataset to investigate the geographic,
temporal, and meteorological characteristics of football
hyperthermia deaths in the United States. In particular, our
study answers the following questions:
&Where do football hyperthermia deaths occur?
&When do deaths occur (annual, intra-seasonally, time of
day, time of practice season)?
&Which athletes (age, position, weight, level of dress) are
most vulnerable?
&Under what meteorological conditions and safety
thresholds do the deaths occur?
Unlike other injuries, hyperthermia deaths are completely
avoidable with proper oversight and precautions. It is hoped
that this study provides empirical evidence that will better
guide safety efforts. We conclude this paper with some
recommendations based on the results of our study.
Materials and methods
Data on heat-related deaths of football players were
obtained from the National Center for Catastrophic Injury
Research (NCCIR; Mueller and Colgate 2010). The dataset
includes information on the death date, age of deceased,
height, weight, school, city, state, and the sport being
played that caused the death. The first death recorded in the
database occurred in 1955 and the last in 2009. We used
19802009 as a study period because deaths before 1980
lacked information in the majority of the data fields.
In order to compile a more complete record of the data,
extensive research was conducted to fill in missing data in
the NCCIR dataset and to add additional information. It is
important to note, however, that no additional deaths were
added to the original NCCIR database. Media reports were
the principal source of information but lawsuit publications
and obituaries were also used. Most of the news articles
were obtained using the LexisNexis academic database.
Local newspapers were contacted for several cases where
no information was found in the LexisNexis database.
Additional data fields were added to the existing
database that would allow better analysis of the conditions
under which the death occurred. These data fields included
the exposure date, time of day the athlete was practicing or
participating in football-related outdoor exercise, the point
in the football season the incident occurred (first day of
practice, etc.), position, pre-existing medical conditions,
type of activity (practice, conditioning workout, etc.),
clothing worn, and latitude/longitude coordinates of expo-
sure location. The exposure date is a critical field for
Int J Biometeorol
assessing the meteorological conditions that were present
during the onset of hyperthermia symptoms. In many cases,
the exposure date and death date were different. Clothing
ensembles were categorized according to Kulka and
Kenney (2002) as full football uniform (helmet, undershirt,
shoulder pads, jersey, and game pants with thigh, knee, and
hip pads), practice uniform (helmet, undershirt, shoulder
pads, jersey, and shorts), and shorts only.
Meteorological data were used to assess the environ-
mental conditions under which the fatalities occurred. All
hourly observations of temperature, dew-point temperature,
relative humidity, wind speed, and cloud cover were from
the Integrated Surface Hourly (ISH) dataset (Lott et al.
2001). However, we retrieved data for 19912005 from the
National Solar Radiation Database (NSRDB) because of
ease of use of the dataset (NREL 2007). Meteorological
observations were obtained from the nearest station to the
location where the exposure occurred. Fatalities were only
examined, however, if an observing station was within
50 km and recorded data during the approximate exposure
time. The average distance between the station and the
heat-related death was 19.2 km, with a standard deviation
of 13.8 km.
We reconstructed meteorological conditions during the
approximate exposure period. While the exact exposure
time was not available for the majority of the cases,
whether it occurred at a morning or afternoon practice
was often indicated. Thus, two time periods were defined: a
morning session was assumed to occur somewhere between
8:00 am and 12:00 pm local daylight time (LDT), and an
afternoon session was assumed to occur somewhere
between 2:00 and 6:00 pm LDT. For these time periods,
the maximum temperature, relative humidity and dew-point
temperature at the time of maximum temperature, the
average temperature, average dew-point temperature, aver-
age relative humidity, and average cloud cover were
calculated. Two derived meteorological variables, the
WBGT and the Heat Index (HI), were computed using the
average morning or afternoon data. As noted earlier,
WBGT is a widely used measure of environmental con-
ditions assessed for safety standards in athletics and
industry (Cooper et al. 2006). We used the software
package Heat Stress Advisor (Zunis Foundation 2010)
which uses algorithms developed by Coyle (2000)to
convert standard meteorological variables (e.g., air temper-
ature, relative humidity, cloud cover) to the wet bulb globe
temperature (WBGT). The Heat Index is based on the
apparent temperature by Steadman (1979) and modified for
operational purposes by the U.S. National Weather Service
(NWS). The NWS issues heat-health warnings based on the
HI and it is therefore familiar to people in the United States.
An empirical equation by Schoen (2005), requiring air and
dew-point temperatures, is used to compute the HI.
Spatial and temporal patterns
Heat-related football deaths were first examined geograph-
ically (Fig. 1). The fatalities were widespread across the
eastern U.S. in a belt that extends along the central East
Coast southward and westward across the Southeast into
Texas. Only five deaths occurred in the drier western U.S.
(southern California and Arizona), whereas no deaths were
reported in New England.
Over the study period, there were 58 reported deaths of
football players from heat-related causes. On average, there
were almost two deaths per year with a standard deviation
of 1.66 deaths. The greatest number of recorded fatalities
was six in 2008. There is an apparent increase in the
number of deaths over time, particularly since the mid-
Fig. 1 Football hyperthermia
deaths, 19802009. Filled
circles are deaths that occurred
in locations with meteorological
observing stations within 50 km
Int J Biometeorol
1990s (Fig. 2a). The 19801994 period had an average of
1.07 deaths per year compared with the 19952009 period
with an average of 2.8 deaths per year.
A number of factors individually or in combination may
help to explain the broad increase in fatalities over time.
First, there has been an increase in athletes participating in
football which would increase the pool of players who may
be susceptible to harm. Available data from National
Federation of State High School Associations (NFSH)
indicates that the number of high school football players
has increased by almost 18% from 19802006 to a total of
1,105,583 players (NFSH 2010). Using the NFSH data as a
metric for overall participation, we note that the pattern of
deaths per 100,000 football players is similar to that of
overall deaths, with greater values after the mid-1990s
(Fig. 2b). Thus, the increase in players participating in
football does not seem to be a major factor in the increase
in deaths. A second explanation is that there has been a
change in the characteristic of the athletes that makes them
more susceptible to heat-related illnesses. Football players
at all levels of competition and particularly linemen have
increased in size over time (Wang et al. 1993; Noel et al.
2003; Secora et al. 2004; Kraemer et al. 2005). Wang et al.
(1993), for instance, showed a distinct increase in the size
of high school linemen from a body mass index (BMI) of
27.7 in 1963 to 32.0 in 1989. Additionally, Noel et al.
(2003) notes that Division I college football players have
become bigger and fatter than they were in the 1980s and
early 1990s. It is possible, then, that the greater size would
increase heat storage and therefore the possibility of heat-
related illnesses. Finally, several studies have identified
climate conditions becoming hotter and more humid across
much of the central and eastern U.S. over different study
periods such as 19611995 (Gaffen and Ross 1999), 1949
1995 (Gaffen and Ross 1998), and 19762004 (Dai 2006).
Climate change over our study period was investigated
using an approach similar to Gaffen and Ross (1998)in
which we computed trends in the number of August days
that exceed a local threshold (85th percentile) for maximum
and minimum daily apparent temperatures (NCDC 2010;
Fig. 3). There are few statistically significant trends for
maximum apparent temperatures but widespread positive
trends are evident in minimum apparent temperatures,
particularly across parts of the southern and eastern U.S.
The implication is that there are a greater number of days
where morning practices have stressful meteorological
conditions and thus an increased risk for heat-related
Intra-seasonally, the largest number of deaths occur in
JulySeptember, with August comprising by far the greatest
number of deaths with approximately 66% (Table 1). A
closer examination of August shows that 71% of August
deaths occur in the first 2 weeks of the month (Table 1). As
early August is often the starting time for pre-season
training, it is possible that acclimatisation to hot and humid
conditions may be an important component in these heat-
related deaths. In 13 cases, news reports specifically noted
that the death occurred within the first 3 days of practice.
Finally, the time of day of the exposure occurred was
reported in 36 cases. Over half the cases (~58%) occurred
in the morning, when temperatures are generally lower but
relative humidities are higher.
Athlete characteristics
Athlete characteristics including age, weight, position, and
clothing worn during the exposure period were examined
(Table 2). The average age was 16.76 years with a standard
deviation of 2.83 years. Most of the athletes were age 18 or
younger, comprising almost 86% of the total deaths. The
athletes were heavy, with an average weight (BMI) of
113.96 kg (33.60) and a standard deviation of 21.76 kg
(5.13). All but three athletes exceeded 90 kg and 95% of
them would be classified as overweight or obese based on
Fig. 2 Time series of atotal football hyperthermia deaths and b
deaths per 100,000 players. Deaths were normalized using data on the
number of high school football players from the period 19802006
Int J Biometeorol
the BMI. The BMI does not distinguish between adipose
and lean tissue, and can be misleading in muscular athletes,
but Laurson and Eisenmann (2007) note that the BMI
correlates well with fat mass for boys aged 1117.
For further analysis, the positions were aggregated as
linemen (offensive and defensive), backs (two fullbacks, one
running back, one defensive back), and other (one wide
receiver). Among American-style football players, offensive
and defensive linemen tend to be the largest players on the
field with higher levels of body fat percentage and greater
absolute strength (Pincivero and Bompa 1997). Offensive and
defensive linemen tend to mirror each other by position, with
offensive linemen attempting to protect the passer and clear
the way for runners to advance the ball while defensive
Table 1 Temporal patterns of football hyperthermia fatalities
Time of day nTime of season nMonth nSub-month (JulSep) n
Morning (8:00 am12:00 pm LDT) 21 1st practice 9 JanMay 1 Jul 115 7
Afternoon (2:006:00 pm LDT) 15 2nd practice 3 Jun 0 Jul 1631 9
Unknown 22 3rd practice 1 Jul 10 Aug 115 27
1st practice with pads 1 Aug 37 Aug 1631 11
Unknown 44 Sep 9 Sep 115 4
Oct 1 Sep 1630 2
NovDec 0
LDT Local daylight time
Fig. 3 Trends in frequency of
August days that exceeded the
local 85th percentile in amaxi-
mum apparent temperature and
bminimum apparent tempera-
ture from 19802009. Filled
(open) circles are positive (neg-
ative) trends at p0.05 and
crosses are stations with no
Int J Biometeorol
linemen try to disrupt the passer and tackle any running
backs before they can gain yardage. Offensive and defensive
backs along with wide receivers tend to have lower body fat
levels and lower absolute strength, but are faster and have
greater aerobic capacity (Pincivero and Bompa 1997).
In our dataset, linemen had an average weight (BMI) of
120.07 kg (34.75) comparedwith 105.91 kg (31.85) for backs.
For reference, we compared the BMI of 23 linemen 18 years
of age with an extensive dataset of 3,683 high school linemen
compiled by Laurson and Eisenmann (2007)(Table2). The
linemen who died from heat-related illnesses were large,
with approximately 87% classified as obese (BMI >30)
compared with 30% in the Laurson and Eisenmann (2007)
dataset. Also, linemen represent a large and disproportionate
percentage of deaths (86%) relative to their numbers on the
field (45%). Finally, we considered the level of dress of the
athletes. Of the 20 cases with data, 8 were in in shorts only,
8 were in practice gear, and 4 were in full football uniforms.
Meteorological conditions
Average meteorological conditions on exposure days were
examined for 33 cases that included the approximate time of
day when the athlete was practicing and were within 50 km of
a meteorological station (Table 3). Days were separated into
morning (8:00 am12:00 pm LDT) or afternoon (2:00
6:00 pm LDT) for analysis. Temperatures on exposure days
ranged from a moderate 23°C up to a very hot 39°C.
Conditions were generally humid, with dew-point temper-
atures averaging 19°C in the afternoon and 21°C in the
morning. Afternoon practices were hotter with average
temperatures of approximately 33°C, almost 5°C greater
Table 2 Characteristics of football hyperthermia fatalities. Percent of High School (HS) linemen is rounded to the nearest percent and based on
data in Laurson and Eisenmann (2007)
Age nWeight (kg) nBMI All linemen nLinemen 18 years
n(%/%HS linemen)
Position nClothing n
11 1 <70 2 <20 1 1 (4/1) Lineman 32 Full uniform 4
12 0 70<80 1 2024 1 0 (0/28) Backs 4 Practice uniform 8
13 4 80<90 1 Overweight (2529) 7 2 (9/41) Other 1 Shorts only 8
14 4 90<100 8 Obese Class I (3034) 18 8 (35/21) Unknown 21 Unknown 38
15 7 100<110 5 Obese Class II (3539) 9 8 (35/7)
16 10 110<120 7 Obese Class III (40) 6 4 (17/2)
17 18 120<130 10 Unknown 3
18 4 130<140 5
19 1 140<150 0
20 1 150<160 2
21 2 160<170 1
22 1 Unknown 16
Only two deaths with the athlete in full uniform had corresponding data on time of death and were within 50 km of a meteorological observing station
Table 3 Average meteorological conditions on days with hyperthermia deaths
Air temperature
Relative humidity
Dew-point temperature
Heat index
Afternoon (14 cases) Mean 32.9 48.3 18.9 30.2 35.0
Median 32.4 51.7 19.9 30.0 35.6
Maximum 39.2 77.9 24.8 33.5 40.3
Minimum 26.1 16.8 9.7 25.2 26.4
Standard deviation 3.9 18.4 4.9 2.4 3.7
Morning (19 cases) Mean 27.8 66.6 20.5 27.7 30.2
Median 27.1 71.2 22.0 27.7 29.9
Maximum 35.4 86.0 25.7 31.8 36.5
Minimum 23.1 33.3 11.0 23.6 23.5
Standard deviation 3.0 14.2 3.8 2.4 3.8
Int J Biometeorol
than the average morning temperature of 28°C. Morning
practices, however, had considerably greater relative humidity
values that were nearly 20% greater (67 vs 48%) than those in
the afternoon. The WBGT and HI were calculated for each
death to integrate the influences of several meteorological
variables. Average WBGT values ranged from approximately
24 to 34°C. Afternoon WBGT values of 30°C were about 2°C
greater than morning values of 28°C. The small difference in
WBGT between morning and afternoon occurs because the
WBGT is very sensitive to humidity levels, which contribute
about 70% of the overall value. The HI ranged from 23 to 40°
C, with average afternoon values of 35°C about 5°C greater
than morning values.
Meteorological conditions were next considered in the
context of established risk thresholds for athletic activity.
Sports Medicine Australia, The American College of Sports
Medicine, and the American Academy of Pediatrics define
categories based on the WBGT (Table 4). All 33 deaths
occurred under conditions considered high or extreme by
both the American College of Sports Medicine and Sports
Medicine Australia, which use similar thresholds. Indeed,
over 60% of the deaths occurred on days where the WBGT
suggested that the practice should be canceled. Under
American Academy of Pediatrics guidelines, 42% of deaths
occurred on days where practices should have been
canceled and another 39% on days when activity should
have been stopped for athletes not acclimatized to high
temperatures and/or high humidity. Overall, the vast
majority of deaths occurred in categories where the threat
for heat-related illnesses were high. Very few deaths
occurred under low or moderate risk conditions. The
NWS has established risk thresholds based on the HI
(Table 4). Deaths occurred under conditions with no safety
advisory (15%), caution (30%), and extreme caution (55%).
Of interest is that 45% of deaths occurred on days with no
safety warning or one at the lowest level of risk for a heat-
related illness (i.e. caution), and no deaths occurred on days
categorized as the most dangerous (i.e., danger and extreme
danger). The lower level of threat suggested by the HI is
likely related to assumptions used in its calculation,
including that an individual is in the shade, of average size
(1.7 m and 67 kg), is dressed lightly (i.e. wearing long
trousers and a short sleeve shirt), and engaged in light
activity (i.e. walking at about 1.4 m s
) (Steadman 1979;
Rothfusz 1990). Clearly, these assumptions are not repre-
sentative of football players who tend to be larger, exposed
to sun, may be dressed in protective gear, and involved in
greater levels of activity. Thus, the HI may underestimate
the environmental risk for athletes such as football players.
Finally, it is important to note that average values were used
to represent the integrated conditions over the practice
period and that the athletes may have been exposed to
higher instantaneous WBGT or HI values.
Third, meteorological conditions were investigated with
regard to the type of clothing the athletes were wearing during
exposure. Kulka and Kenney (2002) established thresholds
for uncompensable heat stress for full pads, practice gear,
and shorts using air temperature and relative humidity. These
thresholds are plotted as curves in Fig. 4.Weanalyzed18
cases (8 with shorts only, 8 with practice gear, and 2 with full
uniforms) that included the level of clothing, the approximate
time of heat exposure, and were located within 50 km of a
meteorological station. For comparison, 16 cases without
data on clothing but with time of exposure were included.
Maximum morning or afternoon temperatures along with the
relative humidity at the maximum temperature, representing
the worst possible conditions the athlete would have
experienced, are plotted for each case in Fig. 4. All but one
of the athletes dressed in shorts only fell below the
established threshold for uncompensable heat stress, indicat-
ing that conditions should have been safe. It should be noted
that two of the athletes had pre-existing medical conditions
(i.e., a rare hemoglobin disorder and sickle cell anemia) that
may have made them more vulnerable to a heat-related
illness. Five of the eight deaths for athletes who were
wearing practice uniforms fell above the threshold. Of the
Table 4 Statistics on football hyperthermia fatalities by risk category
American College of
Sports Medicine and
Sports Medicine Australia
Count (%) American Academy
of Pediatrics
Count (%) NWS Heat
Count (%) Uncompensable
heat stress
Low (<18°C) 0 (0) No limits (<24°C) 1 (3) No warning (<26.7°C) 5 (15) Full uniform
Moderate (1823°C) 0 (0) Longer rest periods
5 (15) Caution
10 (30) Practice uniform
High (2328°C) 13 (39) Stop activity if not
acclimatized (2629°C)
13 (35) Extreme caution
18 (55) Shorts only
Extreme/Cancel event
20 (61) Cancel event (>29°C) 14 (42) Danger (40.754.4°C) 0
Extreme danger
Int J Biometeorol
remaining three incidents, one was near the established
threshold. Finally, athletes were wearing full football uni-
forms in two cases. Conditions fell above the threshold in
one case and below on the other. When considering incidents
with only data on time of exposure, approximately 88%
occurred at levels that are unsafe for full uniform and 75% at
levels unsafe when wearing practice uniforms. All but one of
the deaths, however, occurred at levels below the uncom-
pensable heat stress for shorts only.
Integrated exposure conditions over the morning or
afternoon for clothing specific standards were investigated
using WBGT thresholds adapted by Coyle (2003) from the
temperature and relative humidity thresholds of Kulka and
Kenney (2002). The WBGT categories involve a range of
values because of the interaction between temperature and
relative humidity. Nevertheless, the results using the lower
and upper WBGT thresholds for each clothing category were
identical (Table 4). Here, one of the two athletes in a full
uniform practiced in conditions that exceeded the level of
uncompensable heat stress, five of the eight athletes in practice
gear were exposed to conditions that exceeded the threshold,
and only two athletes in shorts exceeded the threshold.
An important question is whether the environmental
conditions on days with fatalities were atypically harsh. For
each of the 33 fatalities with an approximate time of
exposure, we constructed a climatology of meteorological
conditions using data from 19912005 for the particular
day of the year on which the death occurred. Only 31
stations, however, had sufficient data for a climatological
analysis. The air temperature and dew-point temperature on
the day a death occurred were then standardized relative to
the local climatology. In general, conditions on days with
hyperthermia deaths were both hotter and more humid than
normal (Fig. 5). Over 80% of days had temperatures greater
than the mean and almost 42% of those days were 1
standard deviation above average. Similarly, about 68% of
dew-point temperatures were above the mean and approx-
imately 32% were 1 standard deviation above average.
Finally, drier than normal conditions on some days did not
necessarily alleviate the stressful meteorological conditions
because most of those days (about 78%) were also hotter.
Discussion and conclusions
From 1980 to 2009, 58 football players died from heat-
related illnesses. Our results create a temporal, demograph-
ic, and meteorological profile of hazardous conditions for
football hyperthermia deaths. Consistent with findings by
Cooper et al. (2006) and Fox et al. (1966), heat-related
injuries are most prominent in the first half of August, when
unconditioned and unacclimatized players begin pre-season
practice under hot and humid conditions. Over half the
deaths occur during morning practices which, although
cooler, have higher humidity levels that increase heat stress.
The level of dress has been a concern in studies of football
players and heat stress as helmets and pads can inhibit
cooling mechanisms. Many of the deaths, however, were
among players wearing no pads and minimal clothing.
Finally, consistent with Fox et al. (1966), large linemen,
especially those with BMIs exceeding 30, are dispropor-
tionately represented among the deaths.
Meteorologically, the fatalities occurred on days that
tended to be unusually hot and humid by local standards.
Fig. 4 Football hyperthermia deaths during 19802009 in the context
of uncompensable heat stress limits for different levels of clothing.
The curves are derived from data in Kulka and Kenney (2002). Solid
lines are fit to observed data and dashed lines are extrapolations.
Thresholds are ordered, respectively, from bottom to top lines for full
football uniform, practice uniform, and shorts only. Filled symbols
indicate that the athlete had a pre-existing medical condition
Fig. 5 Average morning (8:0012:00 am) or afternoon (2:004:00
pm) air and dew-point temperatures on days with fatalities standard-
ized using climatological conditions for the particular day of the year
that the death occurred upon. Stations with 15 years of data available
for constructing the climatology are shaded black while those with
1014 years of data are shaded gray
Int J Biometeorol
More importantly, the conditions were categorized as
extremely dangerous (i.e., high or extreme risk) for heat-
related illnesses by the American College of Sports
Medicine using the WBGT. The HI, however, tended to
underestimate the degree of hazard as most deaths occurred
under conditions that were assigned lower risk levels.
Football-specific thresholds for uncompensable heat stress
were a useful metric for athletes in practice uniforms but
less so for those dressed in shorts only. Indeed, most of the
deaths for athletes in shorts occurred below the level of
uncompensable heat stress. A possible explanation for this
discrepancy is that the deaths for athletes wearing only
shorts all occurred early in the pre-season (all on or before
8 August), suggesting that a lack of acclimatization may
have made the players more vulnerable to heat-related
illnesses. Too few data on athletes wearing full pads were
available to draw any definitive conclusions.
Coaches should carefully monitor players, particularly big
linemen, early in the practice season. The complete suite of
meteorological conditions, not merely temperature, should be
accounted for when deciding whether to practice and the
intensity of the practice. In particular, coaches should be
aware that simply holding practice in the morning does not
alleviate hyperthermia threats due to higher humidity levels.
Derived measures of heat stress such as the WBGT, along
with established safety thresholds from organizations like the
American College of Sports Medicine, are useful guides for
assessing levels of hazard and in dictating activity levels.
Finally, the great number of deaths early in the pre-season
practice schedule suggests that proper acclimatization is
important. Most of the deaths were among youth athletes
who may have less physical preparation or opportunity for
acclimatization than college-level or professional athletes
(Bergeron et al. 2005). Thus, longer acclimatization periods
may be an important strategy for reducing the number of
hyperthermia-related deaths. Bergeron et al. (2005)offer
suggested acclimatization plans for both high school and
youth football players. At high school level, for instance,
they suggest a 14-day acclimatization plan where coaches
carefully adjust the level of dress, and length and intensity of
practice sessions as the players gain fitness and adapt to the
ambient meteorological conditions.
Acknowledgment We would like to thank Dr. Fred Mueller of the
National Center for Catastrophic Injury Research for kindly providing
data on heat-related deaths of football players.
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Int J Biometeorol
... 4,5,42 Traditionally, WBGT thresholds and activity modifications for risk categories have been established by consensus among experts in thermal physiology and military medicine. 14,48 In recent years, authors [15][16][17] have retrospectively examined the correlation between these risk categories and the incidence of exertional heat-related injuries and fatalities in the United States. Findings from these studies confirm a heightened risk of EHS episodes and fatalities when the risk category indicates the need for event cancellation 17 and an increased number of medical tent evaluations due to EHS when conditions are in higher risk categories. ...
... 14,48 In recent years, authors [15][16][17] have retrospectively examined the correlation between these risk categories and the incidence of exertional heat-related injuries and fatalities in the United States. Findings from these studies confirm a heightened risk of EHS episodes and fatalities when the risk category indicates the need for event cancellation 17 and an increased number of medical tent evaluations due to EHS when conditions are in higher risk categories. 16 However, WBGT thresholds and the prevalence of EHS fatalities vary geographically. ...
... For cases of EHS, individual athlete characteristics, such as position, body mass index, preex- O n l i n e F i r s t isting illnesses or conditions, and use of medications or supplements should also be documented. 4,17 As these data are accumulated, sports injury epidemiologists and clinicians should test the associations between environmental heat risk categories and incidence rate of heat-related injuries so that more refined, evidence-driven policies can be established. Additionally, the validity of AMG thresholds should be reviewed in consultation with biometeorology and meteorology specialists to examine the influence of geographic and regional climatologic characteristics. ...
Objective To develop best-practice recommendations using thermal indices to determine work-to-rest ratios and facilitate further implementation of environmental monitoring for heat safety in secondary school athletics in the United States. Data Sources A narrative review of the current literature in environmental monitoring for heat safety during athletics was conducted by content experts. A list of action-oriented recommendations was established from the narrative review and further refined using the Delphi method. Conclusions Assessment of wet bulb globe temperature at the site of activity throughout the duration of the event is recommended to assist clinicians and administrators in making appropriate decisions regarding the duration and frequency of activity and rest periods. Activity modification guidelines should be predetermined and approved by stakeholders and should outline specific actions to be followed, such as the work-to-rest ratio, frequency and timing of hydration breaks, and adjustment of total exercise duration, equipment, and clothing. Furthermore, integration of exertional heat illness injury data with environmental condition characteristics is critical for the development of evidence-based heat safety guidelines for secondary school athletics. Athletic trainers play an essential role in conducting prospective injury data collection, recording onsite wet bulb globe temperature levels, and implementing recommendations to protect the health and safety of athletes.
... 3 American football players have the highest risk of developing an EHI, 4 and many known risk factors for EHS are common in American football (e.g., overweight; high amounts of lean body mass; compete during the hottest part of the year). [5][6][7] Unfortunately, the equipment worn to protect athletes from injury in American football also predisposes them to EHI. American football equipment covers a large amount of the body's surface area with hard, impermeable materials. ...
... Our search terms were combined with Boolean operators and included the following: • Only studies utilizing T rec to measure body core temperature were included, as it is the most valid measurement of body core temperature during exercise. 1 • Studies with only men, since American football is predominantly a male sport, most EHS deaths in American football occur to males, 5,7 and women respond differently to exertion in the heat than men. 15 Exclusion Criteria ...
... McMurray et al. 10 tested American football athletes who had body fat percentages exceeding 27% and physical characteristics comparable to those football athletes who died of EHS. 7 Having more body weight as adipose tissue would increase the metabolic workload due to the greater mass. Finally, exercise type, intensity, and duration differed between studies. ...
Clinical Scenario: Many American football players have died from exertional heatstroke, one of the leading causes of sudden death in athletes. These athletes are predisposed to exertional heatstroke, in part, because of their protective equipment. Few authors have systematically appraised the research to determine how much faster rectal temperature (Trec) increases when full American football uniforms generally consisting of a helmet, shoulder pads, jersey, pants with padding, socks, shoes, and underwear/compressions (PADS) are worn compared with no uniform so that clinicians can better plan and modify exercise sessions to prevent dangerous Trec (i.e., ≥40.5 °C). Clinical Question: How much faster does Trec increase when men wear a full American football uniform compared with workout clothing during exercise in the heat? Summary of Key Findings: The authors searched the literature for randomized controlled studies with PEDro scores >6 that compared Trec of males wearing PADS to a control uniform during exercise under controlled laboratory conditions. In all four studies, Trec increased faster when PADS were worn during exercise (PADS = 0.052 ± 0.007 °C/min and control = 0.039 ± 0.009 °C/min). The average effect size across studies was 1.4 ± 0.5. Clinical Bottom Line: PADS increase Trec significantly faster than lesser uniform ensembles. Clinicians should factor in equipment and alterations in exercise duration and rest break frequency to help prevent dangerous Trec in American football players. Strength of Recommendation: Given the large effect size and controlled experimental study designs, there is strong evidence that wearing PADS during exercise results in faster increases in body core temperature.
... The threshold is set as 33°C, above which experts in China, the USA, and Australia advise against outdoor physical activities because of the high risk of heat illness, 14,19,20 and above which deaths from hyperthermia are likely to increase. 21 In 2021, AHL reached 2·04 hours in all age groups, and 1·99 hours in people older than 65 years, representing an increase of 48·2% (0·7 hours) for all age groups, and 41·2% (0·6 hours) in people older than 65 years, compared with the baseline period (1986-2005; figure 1). People in south central China were affected the most, with 3·94 hours lost in 2021, and had the highest annual average growth rate (2·1%) during 2000-21. ...
... Extreme rainfall poses immediate dangers, as well as long-term negative effects that result from displacement and deterioration of living conditions, 23 whereas prolonged drought affects human health by reducing water supply and agriculture yield. 24 In this report, new data and methods were used to map extremes of precipitation across China, including extreme rainfall and meteorological drought (appendix pp [18][19][20][21]. Compared with baseline years (1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005), Qinghai, Sichuan, and Heilongjiang had the largest increase in extreme rainfall events during 2000-2020, while Tibet, Xinjiang, and Sichuan recorded the largest increase in drought occurrence (appendix p 21). ...
Full-text available
A health-friendly, climate resilient, and carbon-neutral pathway would deliver major benefits to people's health and wellbeing in China, especially for older populations, while simultaneously promoting high-quality development in the long run. This report is the third China Lancet Countdown report, led by the Lancet Countdown Regional Centre based in Tsinghua University. With the contributions of 73 experts from 23 leading institutions, both within China and globally, this report tracks progress through 27 indicators in the following five domains: (1) climate change impacts, exposure, and vulnerability; (2) adaptation, planning, and resilience for health; (3) mitigation actions and health co-benefits; (4) economics and finance; and (5) public and political engagement. From 2021 to 2022, two new indicators have been added, and methods have been improved for many indicators. Specifically, one of the new indicators measures how heat affects the hours that are safe for outdoor exercise, an indicator of particular relevance given the boom in national sports triggered by the summer and winter Olympics. Findings in this report, which coincide with the UN Framework Convention on Climate Change 27th Conference of the Parties (COP27) hosted in Egypt (where much attention is being focused on adaptation for clinically vulnerable populations), expose the urgency for accelerated adaptation and mitigation efforts to minimise the health impacts of the increasing climate change hazards in China.
... It has been shown that the incidence of EHIs increases when wet bulb globe temperature (WBGT), a measure of heat stress in direct sunlight, is higher than usual (Cooper et al., 2016). In a retrospective analysis on hyperthermia deaths in American football players, all deaths occurred under "high" or "extreme" conditions as measured by the WBGT (Grundstein et al., 2012), though the level of WBGT that leads to death varies depending on regional climate and acclimatization (Grundstein et al., 2018). Generally, atypically high solar radiation, temperature and humidity conditions can increase the risk of EHIs. ...
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Extreme heat is a recognized threat to human health. This study examines projected future trends of multiple measures of extreme heat across Texas throughout the next century, and evaluates the expected climate changes alongside Texas athletic staff (coach and athletic trainer) attitudes toward heat and climate change. Numerical climate simulations from the recently published Community Earth System Model version 2 and the Climate Model Intercomparison Project were used to predict changes in summer temperatures, heat indices, and wet bulb temperatures across Texas and also within specific metropolitan areas. A survey examining attitudes toward the effects of climate change on athletic programs and student athlete health was also distributed to high‐school and university athletic staff. Heat indices are projected to increase beyond what is considered healthy/safe limits for outdoor sports activity by the mid‐to‐late 21st century. Survey results reveal a general understanding and acceptance of climate change and a need for adjustments in accordance with more dangerous heat‐related events. However, a portion of athletic staff still do not acknowledge the changing climate and its implications for student athlete health and their athletic programs. Enhancing climate change and health communication across the state may initiate important changes to athletic programs (e.g., timing, duration, intensity, and location of practices), which should be made in accordance with increasingly dangerous temperatures and weather conditions. This work employs a novel interdisciplinary approach to evaluate future heat projections alongside attitudes from athletic communities toward climate change.
... This points to the effectiveness of the HI and HI-based warnings imparting behavioral responses when hazardous heat symptoms begin to develop. On the other hand, in a study investigating hyperthermia deaths in American football players, Grundstein et al. (2012) showed that mortality was associated with values of HI deemed a low threat for heat-related illness, while another index, the wet bulb globe temperature (WBGT), performed much better in predicting heat-related deaths, likely due to the WBGT's ability to account for radiative heat gain. While other past studies have examined the ability to use HI in industrial safety settings (Bernard and Iheanacho 2015), to our knowledge there has been no study, which determines their suitability in predicting heat stress compensability (upper limits of human heat balance) with empirically gathered data in low-activity settings. ...
Full-text available
Extreme heat events and consequent detrimental heat-health outcomes have been increasing in recent decades and are expected to continue with future climate warming. While many indices have been created to quantify the combined atmospheric contributions to heat, few have been validated to determine how index-defined heat conditions impact human health. However, this subset of indices is likely not valid for all situations and populations nor easily understood and interpreted by health officials and the public. In this study, we compare the ability of thresholds determined from the National Weather Service’s (NWS) Heat Index (HI), the Wet Bulb Globe Temperature (WBGT), and the Universal Thermal Climate Index (UTCI) to predict the compensability of human heat stress (upper limits of heat balance) measured as part of the Pennsylvania State University’s Heat Environmental Age Thresholds (PSU HEAT) project. While the WBGT performed the best of the three indices for both minimal activities of daily living (MinAct; 83 W · m ⁻² ) and light ambulation (LightAmb; 133 W · m ⁻² ) in a cohort of young, healthy subjects, HI was likewise accurate in predicting heat stress compensability in MinAct conditions. HI was significantly correlated with subjects’ perception of temperature and humidity as well as their body core temperature, linking perception of the ambient environment with physiological responses in MinAct conditions. Given the familiarity the public has with HI, it may be better utilized in the expansion of safeguard policies and the issuance of heat warnings during extreme heat events, especially when access to engineered cooling strategies is unavailable.
... This points to the effectiveness of the HI and HI-based warnings imparting behavioral responses when hazardous heat symptoms begin to develop. On the other hand, in a study investigating hyperthermia deaths in American football players, Grundstein et al. (2012) showed that mortality was associated with values of HI deemed a low threat for heat-related illness, while another index, the wet bulb globe temperature (WBGT), performed much better in predicting heat-related deaths, likely due to the WBGT's ability to account for radiative heat gain. While other past studies have examined the ability to use HI in industrial safety settings (Bernard and Iheanacho 2015), to our knowledge there has been no study, which determines their suitability in predicting heat stress compensability (upper limits of human heat balance) with empirically gathered data in low-activity settings. ...
Multiple thermal indices have been created to categorize the impact of the ambient environment on human physiology and health. Many of these indices promulgate thresholds that are used to delineate between safe and unsafe thermal environments at rest and during physical activity (exercise, sport, industry, etc.). While some of these thresholds were empirically derived, others were established based on models or theoretical construct with no objective physiological measurements or rationale. In a world where heat is already the leading weather-related cause of death and climate change will exacerbate the effects of extreme heat in the future, it is important to determine if commonly used indices and associated thresholds are able to accurately describe ambient conditions which are thermally safe or unsafe. One physiologically- and biophysically-determined definition of safe environments is based on the upper limit of thermal balance (PSU H.E.A.T. Project). In the present study, young, healthy adults were exposed to a progressive heat stress protocol in an environmental chamber in both hot-dry and warm-humid conditions to determine critical environmental limits of dry-bulb temperature and vapor pressure which could then be compared to other widely used critical heat stress index values. That is, upper environmental limits for human heat balance were compared to common heat stress indices, including wet-bulb temperature (Twb), Heat Index (HI), Wet Bulb Globe Temperature (WBGT), and Universal Thermal Comfort Index (UTCI). Under activities of daily living, HI and WBGT thresholds very nearly match up with heat stress compensability curves based on critical heat balance limits while large variation was found in with UTCI. Interestingly, the theorized Twbthreshold of 35°C, used increasingly by mainstream media sources in describing extreme heat, was significantly higher than the critical limit for heat stress compensability. This work highlights the need for continued empirical work in determining and validating existing critical heat stress index thresholds as well as the need for better communication to the general public of what each heat stress index means for their environmental health and safety in a warming world.
... 23 Between 1980 and 2009, EHS was confirmed as a cause of death of 58 US football players. 24 Morbidity Nationally, between 1997 and 2006, an estimated 54,983 patients were treated in US emergency departments for exertional ERI. 25 The number of EHI increased significantly from 3,192 in 1997 to 7,452 in 2006, representing a 133.5% increase. 25 Based on 2001 to 2009 data, CDC estimated that 6,000 people of all ages in the US each year sought emergency treatment for nonfatal EHIs while playing sports or participating in other outdoor recreational activities. ...
Climate change has led to increased frequency, intensity, and duration of extreme heat events with dire consequences for health. These are the deadliest of climate change impacts with preventable mortality from heat-related illnesses and increased threat to safe participation in physical activity and sports. Nurse practitioners can collaborate with community and professional sports health organizations to ensure evidence-based health and safety policies to reduce health-related risks. Adverse consequences on engagement in key health-promoting physical activity and sports may catalyze urgent action to address climate change.
... Additionally, these systems do not account for variations due to the activity patterns of individuals moving through indoor and outdoor environments and other factors including acclimatization, dehydration, medications, and health conditions [12]. For example, a study of USA football player deaths found that 100% of heat-related deaths occurred in conditions that did not trigger a NWS alert [13]. As a first step to understand the importance of exposure variation in predicting risk at the population level, a more precise measurement of exposure at the individual level is needed. ...
Full-text available
Heatwave warning systems rely on forecasts made for fixed-point weather stations (WS), which do not reflect variation in temperature and humidity experienced by individuals moving through indoor and outdoor locations. We examined whether neighborhood measurement improved the prediction of individually experienced heat index in addition to nearest WS in an urban and rural location. Participants (residents of Birmingham, Alabama [N = 89] and Wilcox County, Alabama [N = 88]) wore thermometers clipped to their shoe for 7 days. Shielded thermometers/hygrometers were placed outdoors within participant’s neighborhoods (N = 43). Nearest WS and neighborhood thermometers were matched to participant’s home address. Heat index (HI) was estimated from participant thermometer temperature and WS humidity per person-hour (HI[individual]), or WS temperature and humidity, or neighborhood temperature and humidity. We found that neighborhood HI improved the prediction of individually experienced HI in addition to WS HI in the rural location, and neighborhood heat index alone served as a better predictor in the urban location, after accounting for individual-level factors. Overall, a 1 °C increase in HI[neighborhood] was associated with 0.20 °C [95% CI (0.19, 0.21)] increase in HI[individual]. After adjusting for ambient condition differences, we found higher HI[individual] in the rural location, and increased HI[individual] during non-rest time (5 a.m. to midnight) and on weekdays.
Marching band (MB) artists frequently spend many hours engaged in outdoor physical activity. Anecdotal evidence and small studies have indicated that MB artists do experience heat-related health problems. Yet, unlike athletes, military personnel, or workers, there is very little research on heat-related hazards among this unique population. Here, we seek to understand the incidence and circumstances under which exertional heat illnesses (EHIs) occur among MB artists over a 31-year period (1990–2020) across the USA. Using an on-line news dataset, we identified 34 separate events and at least 393 total EHIs. Heat syncope (~ 55%) and heat exhaustion (~ 44%) comprised the majority of EHIs, although a small number of exertional heat stroke cases were also reported. EHIs were reported in all types of MB activities with ~ 32% during rehearsal, ~ 29% during parades, ~ 21% during competition, and ~ 15% during a performance. Also, the vast majority of events occurred with high school (~ 88%) marching bands. Finally, EHIs overwhelmingly occurred when the weather was unusually hot by local conditions. In light of these findings, we emphasize the need for MB specific heat polices that incorporate weather-based activity modification, acclimatization, education about EHIs, and access to on-site medical professionals.
Abstrak. Sepakbola dimainkan pada bermacam kondisi lingkungan, tidak terkecuali dengan faktor cuaca yang panas saat berlangsungnya pertandingan, yang bisa menjadi salah satu faktor kunci yang berpengaruh terhadap hasil pertandingan. Contohnya saja kemungkinan besar tim tamu yang bisa menang di negara jazirah Arab didapatkan data menurun 3% setiap kenaikan 1°C temperatur dibandingkan dengan tuan rumah yang secara statistik lebih mudah meraih kemenangan. Skuat tuan rumah telah mengalami aklimatisasi terhadap kondisi lingkungan dan terbiasa dengan bermain di bawah suhu yang panas. Bermain di tempat yang panas dapat meningkatkan laju keringat dan vasodilatasi perifer untuk membuang kelebihan suhu di dalam tubuh, yang dapat berakibat dehidrasi dan kebutuhan metabolisme tubuh yang sedang memerlukan banyak energi. Pada sepakbola level elit tekanan dari faktor lingkungan menjadi perhatian penting baik untuk praktisi maupun pemegang kebijakan sepakbola. Di zona Uni Eropa, pertandingan sering diadakan di cuaca yang panas (contohnya di Madrid, Spanyol, 30◦C). Temperatur yang sering melebihi 30°C (maksimalnya: 35°) contohnya yang terjadi pada Piala Dunia Brazil 2014 dapat membuat para pemain tertekan terhadap kondisi suhu dan mengalami penurunan pada aspek teknis mengumpan sebesar 3%.Kata kunci: sepakbola, lingkungan, panas. Abstract. Soccer is a sport play-able in various condition of environment, and one factor that affects this game is in heat situation, that can be one of key factor that change the match outcome. For the example is the big possibility that visiting team outside Arab countries gone to played at Gulf Region decreased winning possibility 3% for a increased 1°C temperature compared to the home team that easier to win under this circumstances. The home team had already aclimatized with the environment condition and often played in the heat temperature. Played soccer in the heat can increased sweat rate and peripheral vasodilation as a result to released the extra heat from the body, which affected dehidration phase and more metabolism to make more energy. In the elite level, pressure from the enviromental factors attracted the attention of both practitioners and the policy’s holders. In the Uni European Zone, match was usually played in the heat (example: at Madrid, Spain, at 30 degree of celcius). Temperature that exceeds 30 degree of celcius (maximum at 35 degree) for the example at the previous world cup 2014 Brazil could made the players got stressed because of the heat and got problems, one of them is decreased 3% of passing accuracy.Keywords: soccer, environment, heat.
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Climatological annual and seasonal dewpoint, specific humidity, and relative humidity maps for the United States are presented using hourly data from 188 first-order weather stations for the period 1961-90. Separate climatologies were calculated for daytime (three observations per day between 0800 and 1600 LST), nighttime (three observations per day between 2000 and 0400 LST), and the full day (eight observations per day, every 3 h). With extended datasets for the period 1961-95, trends in these same variables and temperature are calculated for each of 170 stations and for eight regions of the country. The data show increases in specific humidity of several percent per decade, and increases in dewpoint of several tenths of a degree per decade, over most of the country in winter, spring, and summer. Nighttime humidity trends are larger than daytime trends. The specific humidity increases are consistent with upward temperature trends. The upward temperature and humidity trends are also consistent with upward trends in apparent temperature, a measure of human comfort based on temperature and humidity. Relative humidity trends are weaker than the specific humidity trends, but they do show evidence of increases, especially in winter and spring. The possibility that the detected trends may be artifacts of changes in instrumentation was examined, but several lines of reasoning suggest that they are not. Anthropogenic water vapor produced from fossil fuel consumption, both locally and globally, is too small a source to explain the observed trends.
For morphologic and physiologic reasons, exercising children do not adapt as effectively as adults when exposed to a high climatic heat stress. This may affect their performance and well-being, as well as increase the risk for heat-related illness. This policy statement summarizes approaches for the prevention of the detrimental effects of children's activity in hot or humid climates, including the prevention of exercise-induced dehydration.
In situ observations of surface air and dewpoint temperatures and air pressure from over 15 000 weather stations and from ships are used to calculate surface specific (q) and relative (RH) humidity over the globe (60°S-75°N) from December 1975 to spring 2005. Seasonal and interannual variations and linear trends are analyzed in relation to observed surface temperature (T) changes and simulated changes by a coupled climate model (namely the Parallel Climate Model (PCM)) with realistic forcing. It is found that spatial patterns of long-term mean q are largely controlled by climatological surface temperature, with the largest q of 17-19 g kg1 in the Tropics and large seasonal variations over northern mid- and high-latitude land. Surface RH has relatively small spatial and interannual variations, with a mean value of 75%-80% over most oceans in all seasons and 70%-80% over most land areas except for deserts and high terrain, where RH is 30%-60%. Nighttime mean RH is 2%-15% higher than daytime RH over most land areas because of large diurnal temperature variations. The leading EOFs in both q and RH depict long-term trends, while the second EOF of q is related to the El Niño-Southern Oscillation (ENSO). During 1976-2004, global changes in surface RH are small (within 0.6% for absolute values), although decreasing trends of 0.11% 0.22% decade1 for global oceans are statistically significant. Large RH increases (0.5%-2.0% decade1) occurred over the central and eastern United States, India, and western China, resulting from large q increases coupled with moderate warming and increases in low clouds over these regions during 1976-2004. Statistically very significant increasing trends are found in global and Northern Hemispheric q and T. From 1976 to 2004, annual q (T ) increased by 0.06 g kg1 (0.16°C) decade1 globally and 0.08 g kg1 (0.20°C) decade1 in the Northern Hemisphere, while the Southern Hemispheric q trend is positive but statistically insignificant. Over land, the q and T trends are larger at night than during the day. The largest percentage increases in surface q (1.5% to 6.0% decade1) occurred over Eurasia where large warming (0.2° to 0.7°C decade1) was observed. The q and T trends are found in all seasons over much of Eurasia (largest in boreal winter) and the Atlantic Ocean. Significant correlation between annual q and T is found over most oceans (r 0.6-0.9) and most of Eurasia (r 0.4-0.8), whereas it is insignificant over subtropical land areas. RH-T correlation is weak over most of the globe but is negative over many arid areas. The q-T anomaly relationship is approximately linear so that surface q over the globe, global land, and ocean increases by 4.9%, 4.3%, and 5.7% per 1°C warming, respectively, values that are close to those suggested by the Clausius-Clapeyron equation with a constant RH. The recent q and T trends and the q-T relation- ship are broadly captured by the PCM; however, the model overestimates volcanic cooling and the trends in the Southern Hemisphere.
A simplified scale of apparent temperature, considering only dry-bulb temperature and humidity, has become known as the temperature humidity index (THI). The index was empirically constructed and was presented in the form of a table. It is often useful to have a formula instead for use in interpolation or for programming calculators or computers. The National Weather Service uses a polynomial multiple regression formula, but it is in some ways unsatisfactory. A new model of the THI is presented that is much simpler---having only 3 parameters as compared with 16 for the NWS model. The new model also more closely fits the tabulated values and has the advantage that it allows extrapolation outside of the temperature range of the table. Temperature humidity pairs above the effective range of the NWS model are occasionally encountered, and the ability to extrapolate into colder temperature ranges allows the new model to be more effectively contained as part of a more general apparent temperature index.
Now that summer has spread its oppressive ridge over most of the Southern Region, NWS phones are ringing off their hooks with questions about the Heat Index. Many questions regard the actual equation used in calculating the Heat Index. Some callers are satisfied with the response that it is extremely complicated. Some are satisfied with the nomogram (see Attachment 1). But there are a few who will settle for nothing less than the equation itself. No true equation for the Heat Index exists. Heat Index values are derived from a collection of equations that comprise a model. This Technical Attachment presents an equation that approximates the Heat Index and, thus, should satisfy the latter group of callers. The Heat Index (or apparent temperature) is the result of extensive biometeorological studies. The parameters involved in its calculation are shown below (from Steadman, 1979). Each of these parameters can be described by an equation but they are given assumed magnitudes (in parentheses) in order to simplify the model. # Vapor pressure . Ambient vapor pressure of the atmosphere. (1.6 kPa) # Dimensions of a human. Determines the skin's surface area. (5' 7" tall, 147 pounds) # Effective radiation area of skin. A ratio that depends upon skin surface area. (0.80) # Significant diameter of a human. Based on the body's volume and density. (15.3 cm) # Clothing cover. Long trousers and short-sleeved shirt is assumed. (84% coverage) # Core temperature . Internal body temperature. (98.6°F) # Core vapor pressure . Depends upon body's core temperature and salinity. (5.65 kPa) # Surface temperatures and vapor pressures of skin and clothing. Affects heat transfer from the skin's surface either by radiation or convection. These values are determined by an iterative process. # Activity. Determines metabolic output. (180 W m-2 of skin area for the model person walking outdoors at a speed of 3.1 mph) # Effective wind speed. Vector sum of the body's movement and an average wind speed. Angle between vectors influences convection from skin surface (below). (5 kts) # Clothing resistance to heat transfer. The magnitude of this value is based on the assumption that the clothing is 20% fiber and 80% air. # Clothing resistance to moisture transfer. Since clothing is mostly air, pure vapor diffusion is used here. # Radiation from the surface of the skin. Actually, a radiative heat-transfer coefficient determined from previous studies. # Convection from the surface of the skin. A convection coefficient also determined from previous studies. Influenced by kinematic viscosity of air and angle of wind. # Sweating rate. Assumes that sweat is uniform and not dripping from the body.
Using as bases the amount of clothing needed to achieve thermal comfort and the reduction in the skin's resistance needed to obtain thermal equilibrium, the relative sultriness of warm-humid and hot-arid summer climates is assessed. Conditions of sultriness are referred to a vapor pressure of 1.6 kPa in order to prepare a table of apparent temperature corresponding to summer temperatures and humidities, - Author