Journal of Athletic Training 2018;53(7):696–702
Óby the National Athletic Trainers’ Association, Inc
Exertional Heat Illness
Intended Hydration Strategies and Knowledge of
Exercise-Associated Hyponatraemia in Marathon
Runners: A Questionnaire-Based Study
Thomas Leggett, MBChB*; Jonathan Williams, MSc*; Colm Daly, PhD*;
Courtney Kipps, MSc†; Richard Twycross-Lewis, PhD*
*Centre for Sports and Exercise Medicine, Queen Mary University of London, England; †Institute of Sport, Exercise
and Health, University College London, England
Context: Exercise-associated hyponatremia (EAH) is a
potentially fatal condition that can be prevented by avoiding
excessive fluid intake. Running has become more popular in
recent years, so it is important to assess the safety of runners’
Objective: (1) To explore the intended hydration strategies
of a sample of marathon runners before the 2014 London
Marathon, (2) to examine their sources of information and
knowledge about fluid intake and their understanding of EAH,
and (3) to compare these findings with the results of a similar
study carried out before the 2010 London Marathon.
Design: Cross-sectional study.
Setting: The 2014 London Marathon.
Patients or Other Participants: A total of 298 runners (148
males, 150 females), 0.83% of all race finishers.
Main Outcome Measure(s): Planned frequency, type, and
volume of hydration; sources of information about appropriate
drinking; and understanding of hyponatremia were explored.
Comparisons were made with data collected from a sample of
participants at the 2010 London Marathon. Data relating to the
2014 cohort are presented in descriptive form. Comparisons of
the 2010 and 2014 cohorts were conducted using parametric
and nonparametric methods.
Results: A total of 48.7% of the 2014 cohort listed drinking
to thirst as the most important factor affecting their hydration
strategy during the race. This compared with 25.3% of runners
from the 2010 cohort and represented an increase (v
¼.001); 5.8% of the 2014 cohort planned on drinking more than
3.5 L, compared with 12% of the 2010 cohort (v
Conclusions: The number of sampled individuals using
thirst to guide hydration strategies in the 2014 London Marathon
increased from 2010. However, more than half of the 2014
cohort was not planning to drink to thirst. Runners still need to be
educated about the risks of overdrinking as they continue to
demonstrate a lack of knowledge and understanding.
Key Words: physical endurance, fluid intake, thirst
Since the 2010 London Marathon, education led to improvements in runners’ intended ﬂuid strategies for the 2014
Exercise-associated hyponatremia remains a medically signiﬁcant problem for marathon runners.
More runners currently had safer intended hydration strategies, but a distinct lack of understanding persisted.
Therefore, further education of runners about appropriate ﬂuid intake is still required.
Over the last 2 decades, marathon running has
become an increasingly popular sport.
associated hyponatremia (EAH) is a concerning
and serious medical complication in endurance athletes.
Worldwide, a number of marathon deaths due to EAH have
been recorded, including a young runner in the 2007
London Marathon; 15 runners in the 2003 London
Marathon were admitted to the hospital with EAH.
Exercise-associated hyponatremia is deﬁned as a serum
sodium concentration of less than 135 mmol/L during or up
to 24 hours after prolonged physical activity.
cause is believed to be excessive ﬂuid intake.
serum sodium concentration can be associated with a range
of signs and symptoms, such as nausea, headaches, and
seizures. A sodium concentration of less than 135 mmol/L
will often not result in any physical signs or symptoms but
may still lead to the development of more serious, life-
threatening complications, such as pulmonary or cerebral
edema, unconsciousness, and death. Additional risk factors
for EAH include inappropriate antidiuretic hormone
release and metabolism and extreme environmental
Studies carried out at the 2002 Boston Marathon
2006 London Marathon
indicated that up to 13% of
ﬁnishers had asymptomatic hyponatremia; however, the
point at which asymptomatic athletes become symptomatic
has not been established. Guidance has varied over time as
more research has been undertaken. Previous suggestions
were to base hydration strategies on the sweat rate
authors of a 2017 update
advised drinking to thirst and
using body weight to guide hydration. The use of thirst as a
guide to hydration strategies was widely recommended by
696 Volume 53 Number 7 July 2018
consensus statements and other publications.
earlier investigation by members of our group
the hydration strategies of 217 runners attending registra-
tion for the 2010 London Marathon (0.6% of the total
). The runners lacked knowledge about safe
drinking and prevention of EAH on race day: 12% planned
to drink in excess of 3500 mL during the marathon, a
volume that could have put them at signiﬁcantly higher risk
of developing EAH.
A total of 55 runners (25.3%)
planned to drink according to their thirst. Only 35.5% had a
basic understanding of EAH.
The London Marathon, held in the spring over a ﬂat city
course, is a full 26.2-mi (42.2-km) marathon. Water bottles
(250 mL) were available at 23 water stations situated at 1-mi
(1.6-km)intervals from miles 3 to 25. In addition, stations at 5,
10, 15, 19, and 23 miles distributed 380-mL sachets of sports
energy drinks (Lucozade Sport, Uxbridge, United Kingdom).
Since 2010, efforts have been made to raise awareness of
the risks of overdrinking and EAH. Speciﬁc information is
now provided in the prerace material, which is supplied to
We aimed to explore the intended hydration
strategies of a sample of marathon runners before the 2014
London Marathon, to examine their sources of information
and knowledge about ﬂuid intake and their understanding
of EAH, and to compare these ﬁndings with those of a
similar study carried out before the 2010 London Marathon.
Prior ethical approval for the study was obtained from the
Queen Mary University of London Research Ethics
Committee. Any athlete scheduled to run in the 2014
London Marathon was eligible to be invited to take part at
the event registration. Consistent with the 2010 research
every ninth runner attending was approached at
staggered intervals throughout the 4 registration days and
invited to participate. Runners were given an information
sheet outlining the study. They were excluded if they had
any problems understanding the questionnaire (ie, language
barriers or learning difﬁculty).
Those who agreed to participate were given the study
questionnaire, which was validated in 2010 (see the
and asked to complete it at the research
The questionnaire comprised the following sections:
1. Background demographics
2. Drinking strategies
3. Sources of information about ﬂuid intake
4. Knowledge of EAH
We used SPSS (version 21.0; IBM Corp, Armonk, NY)
for analysis. Data from the questionnaire were presented
descriptively. Chi squared, independent t, and Mann-
Whitney Utests were used to assess the differences in
proportions between data collected in 2010 and 2014.
Findings related to the sources of EAH knowledge were
explored using descriptive statistical methods. A Pvalue of
,.05 was deﬁned as statistically signiﬁcant.
A total of 315 runners were invited to be part of the study
(0.9% of all ﬁnishers
); 17 of these runners did not take
part in the study due to language barriers or lack of time.
The ﬁnal sample was 298 participants (0.83% of all
). Sample demographics are described in Table 1.
The mean ﬁnishing time of the cohort was 4.66 60.49
hours versus 4.50 hours for all the runners in the 2014
Runners were asked to estimate the total milliliters of
ﬂuid they planned to consume over the course of the race.
Those planning to drink more than 3.5 L were deemed to be
at increased risk of EAH. This volume guideline is based on
the ﬁndings of previous studies, which suggested a higher
risk of developing EAH,
and was used in the 2010
The total volume the runners planned to drink
during the race is shown in the Figure.
Overall, 241 (81%) of the 2014 participants speciﬁed the
volume they intended to consume. The median (interquartile
range) volume these runners planned to consume was 1.0(0.4–
1.6) L. Of these 241 runners, 14 (5.8%) planned to drink more
than the 3.5-L threshold compared with 26 runners (12%) in
the 2010 cohort (v
¼4.310, P¼.038; Table 2).
Table 1. Characteristics of the Study Samples
Sample size 217 298
No. declined to
take part 15 17
Mean age, y 38.6 37.5 t¼1.189 .235
Finishing time, h 4.36 60.55 4.66 60.49 t¼2.961 .003
Females 66 (30.4) 150 (50.3) U¼25 892.00 .001
Males 151 (69.6) 148 (49.7)
First marathon 117 (54) 162 (54.4) U¼32 328.00 .997
Member of a
running club 56 (25.8) 83 (27.9) U¼32 994.50 .606
Independent-samples ttest or Mann-Whitney Utest.
Table 2. Comparison of 2010 and 2014 Data for Race Strategies
Variable 2010 Data
2014 Data Statistical Test Value
Hydration strategy during race? No. (%) 208 (95.8) 277 (93) U¼31 108.00 .1050
Median (interquartile range) planned volume consumption during race, L 1.2 (0.6–2.2) 1.0 (0.4–0.6) t¼2.421 .0161
No. of runners intending to drink .3.5 L (%) 26 (12) 14 (5) Z ¼3.216 .0006
Independent-samples ttest, Mann-Whitney Utest, or Z ratio.
Journal of Athletic Training 697
Frequency of Drinking
Runners in the 2014 marathon planned to drink at a
median of 8 (4–11) water stations compared with a median
of 10 (5–24) stations for the runners in the 2010 marathon (t
¼3.353, P¼.001), indicating a reduction in consumption
frequency. Furthermore, a median of 3 (2–5) stations
dispensing sports drinks were intended stops for the 2014
runners compared with a median of 4 (2–5) for the 2010
runners (t¼3.869, P¼.0001; Table 3).
Drinking to Thirst
Thirst was reported as the main factor inﬂuencing the
intended hydration strategy by 145 (48.7%) runners in
2014, which was more than the 55 (25.3%) of runners in
¼29.113, P¼.001; Table 4).
The proportions of female and male runners who planned
on drinking to thirst differed (55% and 43%, respectively;
¼4.365, P¼.037). We found no difference between the
proportions of experienced and nonexperienced runners
¼0.256, P¼.613) planning on drinking to thirst.
Absolute Knowledge. In 2014, 190 (63.8%) runners
claimed to have heard of hyponatremia. However, in
response to the question exploring their knowledge of EAH,
only 70 (40%) demonstrated a basic understanding, as
qualiﬁed by the criteria in Table 5.
Runners’ Self-Perceptions of Their Knowledge. In
total, 258 (86.6%) of the 2014 runners perceived that they
knew enough about safe drinking on marathon day.
Sources of Knowledge
A total of 282 (94.6%) runners claimed to have either
read or been told about appropriate hydration strategies on
marathon day. Most had gained their information from
reading the ofﬁcial prerace information magazine (66.4%),
talking to running friends (40.4%), or reading other running
magazines (30.9%). Most runners had identiﬁed more than
1 source of information. All sources of information are
shown in Table 6.
Exercise-associated hyponatremia is a multifactorial
condition in which consumption of a large amount of ﬂuid
is a recognized risk factor.
Consuming a volume of
3.5 L has been associated with a higher risk of developing
Recent deaths attributed to EAH
highlighted the importance of avoiding overdrinking.
Data collected in 2014 showed that 14 (5%) of the
runners planned to drink more than 3.5 L during the race.
Compared with the previous data from 2010, when 26
runners (12%) planned to drink in this range, this decrease
demonstrated a change in runners’ behavior 4 years later.
This is further highlighted by the reduction in the number
of water stations from which the runners intended to drink
during the race. Both intentions correlated with 2 associated
risk factors for developing EAH.
The current guidance is for a runner to guide ﬂuid intake
based on thirst. It was important to examine what
proportion of the runners planned to use their own thirst
Figure. Volume of ﬂuid (L) runners planned to drink during the
marathon. The horizontal line represents the volume that previous
research has shown may put runners at greater risk of hyponatre-
Table 3. Comparison of 2010 and 2014 Data for Frequency of
Median No. (Interquartile
station visits 10 (5–24) 8 (4–11) 3.353 .0010
visits 4 (2–5) 3 (2–5) 3.869 .0001
Water bottle ¼250 mL, sports sachets ¼380 mL.
Table 4. Comparison of 2010 and 2014 Data for Those Planning to
Drink to Thirst
No. (%) Independent-
Drinking to thirst 55 (25.3) 145 (48.7) 29.1131 .0010
698 Volume 53 Number 7 July 2018
as guidance. In this study, 48.7% of runners listed drinking
to thirst as the most important factor affecting their
hydration strategy throughout the race. Although this was
an increase from 4 years previously, more than half of the
runners in our sample were still not aware of current
guidance regarding thirst as the main indicator for
hydration. This change suggests that messages regarding
hydration are beginning to reach a larger proportion of the
Race inexperience is a known risk factor for EAH.
However, we noted no statistical difference observed
between the numbers of experienced and nonexperienced
runners planning on drinking to thirst. More race
experience does not always equate to a better understand-
ing of the science underlying conditions such as EAH.
This afﬁrms the importance of directing messages and
education about this topic at runners of all experience
We found that 94.6% of runners had read or been told
about hydration on marathon day, and 86.6% perceived
they knew enough about drinking, which might imply that
a similar proportion would plan to drink an appropriate
and safe amount. Yet only 48% planned on drinking to
thirst and only 40% of runners had a basic understanding
of EAH, indicating that the message to runners about
appropriate hydration and EAH still requires further
A total of 66.4% of runners in our sample listed the
ofﬁcial prerace information magazine as a source of
information regarding ﬂuid intake. The 2014 ofﬁcial
magazine contained more prominently placed, detailed,
and speciﬁc advice about appropriate and safe drinking,
including the potential hazards of drinking too much and
EAH. The magazine gave clear instructions to avoid
drinking too much: ‘‘Drinking too much can be very
dangerous and lead to hyponatraemia (water intoxication),
ﬁts [seizures], and even death.’’
Sent to each runner as
part of the ﬁnal preparation before the race, the magazine is
the single most important London Marathon educational
resource. No other speciﬁcally directed information is given
to all runners. Interestingly, the data gathered on sources of
information showed that most runners consulted more than
1 source, including a wide range from magazines to the
Internet and discussions with peers. This fact highlights
how broadly information can be distributed throughout a
community: runners in this case. The message about safe
ﬂuid intake and EAH still needs to be reinforced, and
perhaps more targeted attempts to dispense the information
through the running community would affect runners’
The main limitations of this study were using a
questionnaire and predictive measures and comparing
them with biological factors and outcomes. Exercise-
associated hyponatremia is a multifactorial biological
process affecting the dilution effects of ﬂuids within the
body. A 3.5-L volume was used as a guideline; however, it
is not possible to say that this volume of water should be
used as a deﬁnitive cutoff, as many other factors can
contribute to the development of EAH. The runners in the
2014 study had a difference of approximately 20 minutes
in their average ﬁnishing time, which may have inﬂuenced
the results. Although a low percentage of total ﬁnishers
completed the questionnaire, the numbers were compara-
ble across the 2010 and 2014 studies; we invited every
ninth runner to ensure an equal distribution of runners
across the signup days at the marathon. Results of the
questionnaires depended on the honesty of the respon-
dents, and accuracy cannot be determined; such recall bias
is a general limitation when using questionnaires. The
questionnaire was the same for both studies, and it was
previously validated for the 2010 study, allowing valid
comparisons to be made. The risks and consequences of
EAH are known, but many runners remain unaware of
how much they should drink. More education of runners is
Table 5. Comparison of 2010 and 2014 Data for Runners’
Knowledge of Exercise-Associated Hyponatremia (EAH)
No. (%) Mann-
Heard of EAH 141 (65) 190 (63.8) 31582.50 .756
of EAH 77 (37) 70 (40) 18 620 .865
Runners felt they
knew enough 182 (83.9) 258 (86.6) 33 155.50 .249
Those who mentioned overdrinking, or dilution effects, etc, were
deemed to have a basic understanding of EAH. Understanding of
EAH was deemed ‘‘basic’’ if their answer in free text identified a
cause such as drinking too much fluid or signs and symptoms
included words associated with malaise, collapse, or death, as per
the 2010 study.
Table 6. 2014 Sources of Information for Runners About Fluid Intake on Marathon Day Compared With 2010 Data
No. (%) Mann-Whitney
Read or told about drinking 202 (93.1) 282 (94.6) 32 542.00 .596
Virgin Money London Marathon Magazine 152 (70) 198 (66.4) 30 821.00 .311
Running friends 97 (44.7) 121 (40.4) 30 589.50 .308
75 (34.6) 92 (30.9) 30 750.00 .339
Virgin Money London Marathon Web site 57 (26.3) 71 (23.8) 31 174.00 .488
Running club 36 (16.6; 64% of club runners) 49 (16.4; 59% of club runners) 31 765.00 .801
Information from charity 51 (23.5; 29.1% of charity runners) 62 (20.8; 26.4% of charity runners) 30 741.00 .400
Running coach 30 (13.8) 54 (18.1) 34413.00 .020
Running book 23 (10.6) 46 (15.4) 32 510.00 .641
Other sources of information
34 (15.7) 26 (8.7) 29 764.00 .014
Mostly Runner’s World magazine.
Mainly Internet, social media, or health professional.
Journal of Athletic Training 699
As discussed earlier, information is slowly disseminating
through the running community, but further improvement is
still needed. The most frequently consulted source of
information was the prerace magazine, and this publication
should continue to be used to inform runners. Perhaps a
more targeted approach starting at the grassroots level
would help to increase the understanding of this subject
area among the running community; recommendations
have already been made to broadly target these athletes and
to focus on certain roles within a running community.
Exercise-associated hyponatremia remains a medically
signiﬁcant problem for marathon runners. Education has led
to certain improvements in runners’ intended ﬂuid strate-
gies at the London Marathon, with a statistically signiﬁcant
reduction in the proportion of our cohort planning to drink
greater than 3.5 L and a higher proportion of these runners
now planning on drinking to thirst, as recommended by the
current medical guidelines for endurance athletes. Among
our cohort, 94.6% felt they had enough information and
86.6% perceived they knew enough about safe hydration
strategies. However, only 48% of these runners intended to
drink to thirst, indicating a persistent and distinct lack of
understanding of the topic. More effective education of
runners about appropriate ﬂuid intake and EAH is required
to further reduce the risk and ultimately the incidence of
We thank the participants in this study, the marathon ofﬁcials
who assisted with logistics, and the students from Queen Mary
University of London.
Continued on Next Page
Many thanks for taking part in this questionnaire. If you are not clear about any of the questions, please feel free to ask the researcher.
Please answer the questions in order by putting a tick in the box or writing an answer on the line.
Background information about you as a runner:
1) Is this your first marathon?
Yes _____ (and if Yes, please go to question 3)
If this is not your first marathon, how many previous marathons have you run? (please tick)
10 or more marathons _____
2) What is your fastest time? _____h _____min
3) What is your estimated finishing time? _____h _____min
4) Are you running on behalf of a charity?
If Yes, which charity? ___________________________________________
5) Are you a member of a Running club?
7) Age: _____y
8) How tall are you? _____
9) What is your weight? _____
Information on drinking on marathon day:
10) Have you read about or been told about drinking fluids on marathon day?
No _____ (if No, please go to question 11)
If Yes, where have you received this information from? (please tick all that apply)
London Marathon magazine _____
London Marathon Web site _____
Running club _____
Running coach _____
Running friends _____
Running magazine _____ (if so, which magazine?) ___________________
Running book _____ (if so, which book?) _______________________
From the charity for which you are running _____
Other sources of information (please specify; eg, other online source, smartphone app, library book etc)
700 Volume 53 Number 7 July 2018
Appendix. Continued From Previous Page
Before the marathon:
11) Do you have any plans about drinking in the morning before the start of the marathon?
No _____ (if No, please go to question 15)
12) If Yes, what are you planning to drink? _____________________________
13) How much are you planning to drink? _______________________________
14) When are you planning to drink this? _______________________________
During the marathon:
15) Do you have any plans about drinking during the race?
No _____ (if No, please go to question 19)
16) If Yes, what are you planning to drink? _____________________________
17) How much are you planning to drink? ____________________________
18) At what stages of the race are you planning to drink?
19) Some people carry their own drinks from the start of the race – do you intend to do that?
No _____ (if No, please go to question 25)
20) If Yes, what drink will you carry? _______________________________
21) What volume will you carry? __________________________________
22) Do you plan to drink water provided in bottles at water stations during the race?
No _____ (if No, please go to question 25)
23) If yes, at how many water stations will you take bottles of water? _____
24) How much of each bottle do you anticipate that you will drink?
A few sips _____
Several mouthfuls _____
Half the bottle _____
Most or all of the bottle _____
25) Do you plan to drink the sports drink (Lucozade) provided at the drink stations during the race?
No _____ (if No, please go to question 28)
26) If Yes, at how many drink stations will you take a sports drink? _____
27) How much of each pack do you anticipate that you will drink?
A few sips _____
Several mouthfuls _____
Half the pack _____
Most or all of the pack _____
28) What is the volume of each water bottle given out on the course?
(please estimate if you don’t know exactly) _____mls
29) What is the volume of each pack of sports drinks given out on the course?
(please estimate if you don’t know exactly) _____mls
30) What factors may affect how much you drink in order of importance?
(please mark ’10for the most important for you, ’20for the second, ’30for the third most important and ’4 0for
the least important)
My plan _____
How thirsty I feel _____
The temperature on race day _____
Other (please specify) _____________________________
31) Have you practised drinking water during your training?
32) Have you practised drinking a sports drink during your training?
After the marathon:
33) Do you have any plans about drinking in the 6 hours after the marathon?
No _____ (if No, please go to question 37)
34) If Yes, what are you planning to drink? _____________________________
35) How much are you planning to drink? _____________________________
36) How often are you planning to drink? _____________________________
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Address correspondence to Jonathan Williams, MSc, Centre for Sports and Exercise Medicine, Queen Mary University of London, 80
Slade Road, Portishead, Bristol BS20 6BH, London, England. Address e-mail to firstname.lastname@example.org.
Appendix. Continued From Previous Page
Information about fluids:
37) Do you feel that you know enough about what and how much to drink on marathon day?
If No, what would help you to be better informed for future races?
38) Have you heard of the term ’hyponatraemia’ (low salt or sodium levels)
If Yes, what is your understanding of its causes and effects?
39) Do you have any other comments about drinking fluids on marathon day?
Many thanks for completing this questionnaire. Please return it to the researcher.
The questionnaire is reproduced in its original form except that underlined spaces replaced boxes for answers.
702 Volume 53 Number 7 July 2018