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Sports nutrition guidelines frequently encourage sodium ingestion during endurance exercise, and much work has been undertaken to quantify sweat sodium losses during exercise. However, current guidelines for sodium do not recommend specific quantities, nor provide justification for the effectiveness of sodium to improve endurance performance. A systematic review was undertaken using six databases (CINAHL, Embase, Medline Ovid, Scopus, SPORTDiscus, and Web of Science) to determine the effect of sodium ingestion during exercise on endurance performance. Five studies met the inclusion criteria. They varied in quantity of sodium consumed (280 to 900mg/h), ingestion method (capsules or solutions), fluid intake (programmed or ad libitum) and performance outcomes (time trial, distance-test, time to exhaustion following steady state exercise, and finish time in an organized competition). Only one study reported a significant benefit from sodium ingestion (504mg/h) of 7.8%. All other studies found no significant effect of sodium on performance. Several limitations were found, including different ambient conditions across study days, ad libitum carbohydrate intake that was not reported, and performance measured during an organized competition where other factors may have influenced finish time. No study measured performance in hot ambient conditions (e.g., ≥30°C), and no study quantified each participant’s sweat sodium losses beforehand, thus providing sodium intake as a proportion of expected losses. It is concluded that there is currently minimal evidence that sodium ingestion during exercise improves endurance performance. The limited number and quality of existing studies indicates a need for future work in this area.
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International Journal of Sports Science 2018, 8(3): 97-107
DOI: 10.5923/j.sports.20180803.05
Impact of Sodium Ingestion During Exercise on
Endurance Performance: A Systematic Review
Alan J. McCubbin*, Ricardo J.S. Costa
Department of Nutrition, Dietetics and Food, Monash University, Notting Hill, Victoria, Australia
Abstract Sports nutrition guidelines frequently encourage sodium ingestion during endurance exercise, and much work
has been undertaken to quantify sweat sodium losses during exercise. However, current guidelines for sodium do not
recommend specific quantities, nor provide justification for the effectiveness of sodium to improve endurance performance.
A systematic review was undertaken using six databases (CINAHL, Embase, Medline Ovid, Scopus, SPORTDiscus, and
Web of Science) to determine the effect of sodium ingestion during exercise on endurance performance. Five studies met
the inclusion criteria. They varied in quantity of sodium consumed (280 to 900mg/h), ingestion method (capsules or
solutions), fluid intake (programmed or ad libitum) and performance outcomes (time trial, distance-test, time to exhaustion
following steady state exercise, and finish time in an organized competition). Only one study reported a significant benefit
from sodium ingestion (504mg/h) of 7.8%. All other studies found no significant effect of sodium on performance. Several
limitations were found, including different ambient conditions across study days, ad libitum carbohydrate intake that was not
reported, and performance measured during an organized competition where other factors may have influenced finish time.
No study measured performance in hot ambient conditions (e.g., ≥30°C), and no study quantified each participant’s sweat
sodium losses beforehand, thus providing sodium intake as a proportion of expected losses. It is concluded that there is
currently minimal evidence that sodium ingestion during exercise improves endurance performance. The limited number and
quality of existing studies indicates a need for future work in this area.
Keywords Salt, Sweat sodium, Physical activity, Endurance exercise, Endurance performance
1. Introduction
During endurance exercise, the production of sweat for
purposes of thermoregulation results in significant losses of
body water, as well as electrolytes [1]. Because sodium is
the predominant electrolyte lost through sweating, the
quantification of these losses through sweat collection and
analysis has been the subject of much attention from
researchers [2-9]. It is generally accepted that optimal
replacement of fluid and sodium during endurance exercise
will enhance the rate of fluid absorption and gastrointestinal
comfort, maintain total body water (TBW), plasma volume
(PV) and serum sodium concentration (serum [Na+]) [1].
The maintenance of TBW and PV, through adequate
fluid and/or sodium intake, has been shown to prevent
a performance decline in high intensity endurance
efforts when they follow prolonged steady state exercise,
with TBW losses of as little as 1-2% of initial body mass
* Corresponding author: (Alan J. McCubbin)
Published online at
Copyright © 2018 The Author(s). Published by Scientific & Academic Publishing
This work is licensed under the Creative Commons Attribution International
License (CC BY).
resulting in performance decrements [10, 11]. In contrast,
larger TBW deficits appear to be required before a
reduction in performance is seen in longer, submaximal
endurance efforts [12]. In addition to the effect on body
water, maintenance of blood sodium concentration is
particularly important for the health of the athlete, with the
consequences of exercise-associated hyponatraemia (EAH)
a cause for great concern, especially in ultra-endurance
sports populations [13-15]. Perhaps due to its greater
overall influence on PV and serum [Na+] [13, 16], and
because it is easy to quantify in athletes [17], there has been
significant attention paid to fluid replacement guidelines
during exercise [1, 6]. Despite much effort to collect and
analyse sweat composition in athletes, there are currently no
specific recommendations for sodium replacement during
exercise, with current guidelines stating only that sodium
should be replaced “…when large sweat losses occur…”
Anecdotally, many endurance athletes and their support
teams seek to quantify sweat sodium losses through ‘sweat
testing’ services, with the belief that specific sodium
replacement will improve performance. This belief appears
to include both direct performance benefits from sodium
consumption, or indirect benefits through the prevention of
exercise-associated muscle cramps (EAMC) and/or EAH.
98 Alan J. McCubbin et al.: Impact of Sodium Ingestion During
Exercise on Endurance Performance: A Systematic Review
Commercial sweat composition testing services exist in
many countries, and much work has been undertaken to
improve the validity and reliability of field techniques for
sweat collection and analysis [2, 8, 9, 19, 20]. However, the
dichotomy between well validated sweat composition and
testing protocols, and lack of specific sodium replacement
guidelines, suggests an absence of research examining the
effect of specific sodium replacement during exercise on
subsequent endurance performance. Therefore, the aim of
this systematic review was to determine the impact of
quantifiable sodium replacement during exercise on
endurance performance, either directly or by attenuating
2. Methods
A systematic literature search was undertaken by two
researchers, to determine the impact of sodium replacement
during endurance exercise on measures of performance in
accordance with the Preferred Reporting Items for
Systematic Review and Meta-Analyses (PRISMA) statement
2.1. Search Strategy
A three-step search was undertaken of published
English-language studies in six online scientific databases
from inception to March 2018 (CINAHL, Embase, Ovid
MEDLINE, Scopus, SPORTDiscus, and Web of Science). In
addition, the reference lists of all identified studies and other
known review papers relevant to the topic were searched to
identify additional studies that may have been missed by the
original search. In order to obtain the level of methodological
detail required, book chapters, opinion articles, reviews,
unpublished works, abstracts, short reports, and case-studies
were not considered. The keywords applied in the literature
search are shown in Table 1.
2.2. Eligibility Criteria
Eligibility criteria were established by the researchers
a priori in accordance with the Participant Intervention
Comparator Outcomes Study (PICOS) design format [21].
Original field observational studies and/or
laboratory-controlled trials, presenting quantified data on
endurance performance, within an exercise protocol of more
than 1 h duration, from participants exercising with two or
more levels of sodium intake during exercise were
considered for the review. Studies were suitable for inclusion
if they involved either a time trial or distance-test, or time to
exhaustion performance test, either as the entire exercise
bout or following a period of steady state exercise. After
duplicates were removed, the titles and abstracts were
reviewed by two researchers against the eligibility criteria
(Figure 1).
2.3. Data Extraction
Relevant data was extracted by two researchers and
cross-checked. Variables extracted were the number of
participants, age, training status (years of experience and
O2max where available); dietary intervention (sodium intake
during exercise); exercise protocol used, including
performance test; environmental conditions during the
exercise bout; hydration status before and changes during the
exercise bout; heart rate, perceived exertion, and outcomes
of the performance test. During the data extraction process
eligibility was again checked, and appropriate inclusion or
exclusion action was taken. Any difference of opinion
between researchers during the review process was resolved
by discussion and consensus. Where possible, units were
standardised by simple mathematical conversion. Data were
not considered appropriate for further synthesis into a
meta-analysis due to the absence of homogeneous outcome
2.4. Risk of Bias Assessment
Risk of bias assessment was performed using the
Cochrane ‘Risk of bias’ assessment tool [22]. The tool
assesses the risk of selection bias (due to random sequence
generation and concealment of allocation), performance bias
(from inadequate participant blinding), detection bias
(inadequate personnel blinding), attrition bias (incomplete
outcome data), reporting bias (selective reporting of
outcomes), and other potential forms of bias.
Table 1. Search strategy for the systematic review on the effect of dietary sodium intake during exercise on endurance performance
Field One (combine with OR)
Field Two (combine with OR)
Intervention and Comparison
Field Three (combine with OR) - Outcome
Keywords: Athlet*, Physical
Exertion, Physical Activit*, Exercis*,
MeSH headings: Athletes, Exercise,
Physical Exertion, Physical Activity,
Exercise, Sports
Keywords: sodium*, sodium intake*,
salt intake*, diet* adj2 salt, salt adj2
MeSH headings: Sodium (dietary),
Sodium, Diet (Sodium-restricted)
Keywords:, athletic perform*, endurance
perfor., perform*
MeSH headings: athletic performance,
endurance, endurance capacity
* used to retrieve unlimited suffix variations.
International Journal of Sports Science 2018, 8(3): 97-107 99
Figure 1. PRISMA diagram, showing the inclusion and exclusion of papers in the review
3. Results
3.1. Search Results
The initial database search yielded 4108 non-duplicate
citations. 4097 of these were excluded on title and abstract
screening, leaving 11 papers. Following the full text
screening, five papers met all inclusion criteria and are
included in this review (Table 2).
3.2. Study Characteristics
The five studies investigated the effect of sodium
ingestion during exercise on different aspects of endurance
performance. One study [23] used a time trial, one a
distance-test [24], one time to exhaustion following steady
state exercise [25], and two provided known quantities of
sodium during an organized endurance competition [26, 27].
Each of these performance types will be described
separately. Participants across these studies included both
sexes. Mean or median age varied between studies, from 27
[23] to 40 years [24]. Training experience (in years) or
cardiorespiratory fitness (V
O2max) was not reported in three
of the five studies [24, 25, 27]. All studies were undertaken
in temperate ambient conditions with minimal variation
between interventions, except one study in which the
temperature varied from 2.6-20.6°C across trial days,
resulting in an effect of trial order on performance [24].
Pre-exercise hydration status, by measurement of any
combination of TBW, plasma osmolality, plasma or serum
[Na+], or urine osmolality was reported in all but one study
[25]. The rate of sweat loss and subsequent changes in body
mass were reported in all studies and were not significantly
different between interventions. PV changes were reported
only in one study [23], in which sodium supplementation
increased PV by 1.8%, whilst placebo resulted in a 0.9%
reduction (p < 0.05).
3.3. Dietary Intervention
All studies provided sodium in the form of sodium
chloride. In four of the studies this was provided in capsules
and compared to a placebo capsule that contained no
sodium in a blinded manner [23, 25-27], whilst in the fifth
study [24] sodium was provided unblinded in a solution,
with a high and low sodium concentration as well as a water
only control. The quantity of sodium provided varied
between studies from 280 to 900 mg/h. The quantity
provided per hour was not related to the exercise duration or
ambient conditions. In all studies the amount of sodium
provided was the same for every participant per hour of
exercise, with no individualisation of sodium dose based on
the participant’s body mass, sweat sodium concentration, or
expected sweat sodium losses.
100 Alan J. McCubbin et al.: Impact of Sodium Ingestion During
Exercise on Endurance Performance: A Systematic Review
Table 2. Systematic review search results, showing included papers to determine the impact of sodium ingestion during exercise on endurance
Sodium intake
fluid & CHO
intake during
Change in hydration
Heart Rate (bpm)
and Rating of
Perceived Exertion
9 well trained
(male: 5, female:
Age 27 ± 9 years,
O2max 62 ± 8
Crossover trial:
Na: 280mg/h
given in
capsules (NaCl
or placebo)
Fluid: Ad
Na: 428 ± 166
Placebo: 269 ±
65 mL/h *
consumed not
Na: Tamb 14.0
± 2.1oC,
63% RH
Placebo: Tamb
13.5 ± 2.1oC,
63% RH
cycling TT
Sweat Rate:
Na: 570 ± 220 mL/h
Placebo: 710 ± 290
mL/h NS
Body Mass Loss:
Na: 1.0 ± 0.8%
Placebo: 1.0 ± 0.6%
PV Change:
Na: +1. 8 ± 2.2%
Placebo: -0.9 ±
1.8% *
Pre-ex Plasma
Na: 142 ± 2 mmol/L
Placebo: 140 ± 1
mmol/L *
Mean HR:
Na: 158 ± 9
Placebo: 157 ± 9
72km TT
Na: 171.3 ± 23.5
Placebo: 172.3 ±
23.3 min NS
EAH: None in
either group
26 well trained
male triathletes
Age 37 ± 7 years
Experience 8 ± 3
Na: 504mg/h,
given in
(Saltstick caps
or placebo)
transitions &
bike leg.
Fluid: Ad
Na: 371 ± 78
Placebo: 273 ±
109 mL/h*
Na: 32 ± 14 g/h
Placebo: 40 ±
17 g/h NS
Tamb 22.5 ±
2.7 °C,
36.8 ± 8.3%
Half IM
Sweat Rate:
Na: 781 ± 214 mL/h
Placebo: 721 ± 198
mL/h NS
Body Mass Loss:
Na: 3.4 ± 1.3%
Placebo: 2.8 ± 0.9%
PV not reported
POsm (Na
Pre-ex: 291 ± 4
Post-ex: 304 ± 5
POsm (Placebo):
Pre-ex: 291 ± 6
Post-ex: 300 ± 4
Serum [Na+] (Na
Pre-ex: 142 ± 2
Post-ex: 145 ± 2
Serum [Na+]
HR not reported
Whole-race RPE
Na: 17 ± 2
Placebo: 16 ± 3 NS
Race finish time:
Na: 307 ± 32min
Placebo: 333 ±
40 min *
EAH: Not
International Journal of Sports Science 2018, 8(3): 97-107 101
Pre-ex: 141 ± 1
Post-ex: 143 ± 2
11 experienced
runners/ cyclists
(male: 4, female:
2 cycling, 9
Age 31 ± 12
Crossover trial:
Na: 900mg/h,
given in
capsules (NaCl
or placebo)
Fluid: 400
mL/h for body
wt up to 70kg,
600 mL/h to
body wt
800 mL/h for
body wt >90kg.
CHO: Not
Na: 21.0 ±
34.5 ± 11.0%
Placebo: 21.3
± 0.3°C
34.88 ± 10.6%
running or
cycling at
60% HRR,
by TTE at
Sweat Rate:
Na: 1016 ± 239
Placebo: 1054 ±
278 mL/h NS
Body Mass Loss:
Na: 2.0 ± 0.4%
Placebo: 2.3 ± 0.7%
PV not reported
Peak HR:
Na: 181 ± 13
Placebo: 180 ± 12
Mean RPE during
steady state:
Na: 13 ± 1
Placebo: 13 ± 1 NS
Time To
Na: 6.88 ± 3.88
Placebo: 6.96 ±
3.61min NS
EAH: Not
participant in the
evening after the
Na trial
114 IM
(male: 104,
female: 10)
Age 34 ± 7 years
Na: 284 ± 160
mg/h, given in
capsules (NaCl
or placebo)
Fluid: ad
libitum and not
CHO: ad
libitum and not
Range: Tamb
48-79% RH
Sweat Rate:
Na: 229 ± 102 mL/h
Placebo: 236 ± 134
mL/h NS
Body Mass Loss:
Na: 3.6 ± 1.4%
Placebo: 3.9 ± 2.1%
PV not reported
Serum [Na+] (Na
Pre-ex: 141 ± 2
Post-ex: 142 ± 3
mmol/L NS
Serum [Na+]
Pre-ex: 141 ± 2
Post-ex: 141 ± 4
mmol/L NS
HR not reported
Exercise intensity
(1-10 scale,
converted to 6-20
RPE scale):
Na: 16 ± 9
Placebo: 16 ± 9 NS
Race finish time:
Na: 758 ± 88 min
Placebo: 762 ±
101min NS
EAH: One
participant in the
placebo group
developed EAH.
13 well trained
Age: Median
40 (22-53) years
Crossover trial:
High Na 680
Low Na 410
Water 0 mg/h
Taken in water
with different
Fluid: 1000
mL/h in all
Range Tamb:
differences on
different trial
days, RH not
4 hour
running DT
on outdoor
Sweat Rate:
High Na: 525 ± 250
Low Na: 450 ± 300
Water: 475 ± 475
mL/h NS
Body Mass Loss:
High Na: 3.6 ±
Low Na: 3.1 ± 2.1%
Water: 3.3 ± 3.3%
HR and RPE not
4hr Distance
High Na: 39.9 ±
4.3 km
Low Na: 42.0 ±
4.8 km
Water: 40.6 ± 5.2
km NS
Mild EAH
(plasma [Na+]
High Na: 46% of
102 Alan J. McCubbin et al.: Impact of Sodium Ingestion During
Exercise on Endurance Performance: A Systematic Review
CHO: 60 g/h in
Low Na and
water trials, 63
g/h in High Na
PV not reported
Plasma [Na+]
High Na: 137 ± 1
Low Na: 137 ± 1
Water: 138 ± 2
mmol/L NS
Plasma [Na+]
High Na: 135 ± 3
Low Na: 133 ± 2
Water: 131 ± 2
mmol/L §
Low Na: 69%
Water: 92%
Severe but
EAH (plasma
High Na: 0% of
Low Na: 0%
Water: 17%
EAH: None in
any group
EAH: Exercise-associated hyponatraemia, EAMC: Exercise-associated muscle cramps, Na: Sodium, NaCl: Sodium chloride, CHO: Carbohydrate Tamb: ambient
temperature, RH: relative humidity, TT: time trial, TTE: time to exhaustion, DT: distance-test, IM: Ironman, HRR: Heart Rate Reserve, RPE: Rating of Perceived
Exertion (6-20), PV: Plasma volume, NS: Not significant, Difference pre- to post-exercise, * Difference between sodium intakes (p < 0.05), § Difference between high
Na and water interventions (p < 0.05).
3.4. Effect of Sodium Intake on Time Trial Performance
One study assessed time trial performance in a 72 km
cycling time trial on an outdoor course, including both male
(n= 5) and female (n= 4) athletes. Capsules provided either
280 mg/h or 0 mg/h of sodium, and mean heart rate (p=
0.86) and time trial performance was not different between
interventions (p= 0.46).
3.5. Effect of Sodium Intake on Distance-test
One study assessed the distance covered in four hours
around an outdoor running track in female ultramarathon
runners (n= 13) [24]. In a crossover design, a high and low
concentration of sodium solution were consumed as well as
water in separate trials, in an unblinded fashion. There were
no significant differences in the distance completed
between interventions, however it should be noted that an
effect of trial order was found (p < 0.0001), most likely due
to the variable ambient conditions on each trial day
(temperature range of 2.6-20.6°C across trials).
3.6. Effect of Sodium Intake on Time to Exhaustion
following Steady State Endurance Exercise
One study assessed the time to exhaustion of male (n= 7)
and female (n= 4) endurance athletes during an incremental
exercise test using either stationary cycling with increasing
power output (n= 2), or treadmill running with increasing
gradient (n= 9) in a laboratory setting [25]. The incremental
test was preceded by two hours of steady state cycling or
running at 60% of heart rate reserve. Capsules provided
either 900 mg/hr or 0 mg/hr sodium, and time to exhaustion
was not different between interventions (p= 0.919).
3.7. Effect of Sodium Intake on Performance during
Organized Endurance Competitions
Two studies assessed the effect of sodium intake on
performance during an organized half- (n= 26, all male) [26]
and full-Ironman (IM) triathlon (n= 114, 104 male) [27].
Participants were randomised to consume either sodium or
placebo capsules throughout the race (half-IM 504 mg/h,
IM 284 mg/h). Fluid and carbohydrate (CHO) were
consumed ad libitum in both studies. In the half-IM, fluid
intake was significantly greater in the sodium compared to
placebo group (371 ± 78 and 273 ± 109 mL/h respectively,
p= 0.05) with no significant difference in CHO intake (p=
0.39) [26]. Fluid and CHO intake were not reported in the
IM study [27]. In the Half-IM, mean finish time was 7.8%
faster in the sodium group compared to placebo (p= 0.04)
[26], whereas there was no difference in finish time
between groups in the IM (p= 0.14) [27].
3.8. Effect of Sodium Intake on EAMC and EAH
Only one study reported on the incidence of EAMC,
noting only one participant reported EAMC, in the evening
after the exercise bout was completed, having consumed the
high Na intake during exercise [25]. Three of the five
studies reported incidence of EAH. One reported no cases
of EAH [23]. Another reported a single participant
developing symptomatic EAH requiring hospitalisation,
following excessive fluid ingestion and substantial body
mass gain [26]. A third study reported an incidence of more
than 40% for asymptomatic EAH in participants with no,
low and high sodium ingestion [27], when fluid was
ingested at around double the rate of sweat losses. The
incidence of mild EAH (plasma sodium concentration
International Journal of Sports Science 2018, 8(3): 97-107 103
130-135 mmol/L) was lower with increasing sodium
intake (High Na: 46%, Low Na: 69%, Water: 92%) and
post-exercise plasma sodium concentration was
significantly lower with water compared to low and high
sodium intakes (p < 0.001) [27].
3.9. Risk of Bias Assessment
Results of the risk of bias assessment are shown in Table
3. Selection bias was not evident in any study. Potential
performance and detection bias was observed in one of the
five papers [24], due to a lack of blinding of the sodium
intervention. Potential reporting bias was seen due to
uneven or unreported participant drop outs in two studies
[25, 27], although the effect of this was unclear. The main
sources of bias however came from inadequate control of
ambient conditions and dietary intake, with at least one of
these factors evident in all included studies. Overall none of
the studies were deemed low risk of bias, with three deemed
unclear [25-27] and two high risk of bias [23, 24].
4. Discussion
The ingestion of sodium during endurance exercise is
commonplace and is reflected in the specific inclusion of
sodium in sports nutrition guidelines and many sports
nutrition targeted commercial products [1, 6, 18]. This
systematic review aimed to determine the effect of
quantifiable sodium ingestion during exercise on endurance
performance outcomes. Our search of the literature found
only five studies that met the inclusion criteria, and only
one that suggested a benefit from sodium replacement on
endurance performance [26], at least for the exercise
intensities, durations, and sodium intake doses studied. It
should also be noted that the quality of the included studies
was generally poor, due to variations in ambient conditions
between trial days, and differences in CHO or fluid intake
between interventions.
Table 3. Risk of bias assessment for the systematic review to determine the impact of sodium ingestion during exercise on endurance performance, using
the Cochrane Collaboration’s ‘Risk of bias’ tool [20]
Cosgrove & Black (2013)
Del Coso et al. (2016)
Earhart et al. (2015)
Hew-Butler et al. (2006)
Twerenbold et al.
Randomized crossover
Participants were
pair-matched for age,
experience and best race
time, then randomly
Randomized crossover
Random allocation
crossover design
Randomized crossover
Not stated
Randomized crossover
Not stated
crossover design
Participants and
personnel blinded
Participants and
personnel blinded
Participants blinded.
Personnel blinding not
Participants blinded.
Personnel blinding not
Not blinded.
Personnel blinded
Personnel blinded
Not stated
Not stated
Not stated
outcome data
Drop outs reported and
even across both groups
Incomplete one drop
out due to GI distress
from NaCl capsules, two
due to schedule conflicts
Drop outs described but
not clear from which
Not stated
N/A - only one outcome
measure reported
N/A - only one outcome
measure reported
N/A - only one outcome
measure reported
N/A - only one outcome
measure reported
N/A - only one
outcome measure
sources of
Outdoor time trial on two
separate occasions,
possible differences in
wind speed/direction.
CHO intake ad libitum
but intake not reported.
Fluid intake greater in Na
trial compared to placebo
(p < 0.05).
Fluid intake greater in Na
trial compared to placebo
(p < 0.05). Performance
measured in organized
race with other
competitors, which may
influence performance
CHO intake not reported
presumed to be none
CHO and fluid intake ad
libitum but not reported
possible differences
between groups.
Performance measured in
organized race with other
competitors, which may
influence performance
Large differences
in ambient
between trial days
(by 15oC). Effect
of trial order on
High risk of bias
Unclear risk of bias
Unclear risk of bias
Unclear risk of bias
High risk of bias
104 Alan J. McCubbin et al.: Impact of Sodium Ingestion During
Exercise on Endurance Performance: A Systematic Review
4.1. Study Methodologies
Sweat sodium losses vary significantly between and
within individuals, with sweat fluid losses and sweat
sodium concentration both determinants [2]. These factors
in turn are influenced by exercise mode, intensity, duration
and ambient conditions; body composition; sweat gland
density and distribution; heat acclimation and/or
acclimatisation, and possibly dietary sodium intake [2, 4,
15]. Although four of the five studies provided sodium or
placebo in capsules during exercise, in temperate ambient
conditions, the sodium dose consumed per hour varied by a
factor of three between studies. The amount was not related
to participant body mass, ambient conditions or exercise
duration. We were surprised to find no studies have
attempted to measure the participant’s sweat sodium losses
in well-controlled laboratory conditions, and/or provide
sodium in quantities that represented a specific proportion
of their expected losses. It cannot be determined from the
included studies if the sodium ingested was adequate to
replace a given proportion of sodium losses in some, all or
none of the participants. The arbitrary nature of the sodium
interventions would make interpretation of results difficult,
if indeed there was a dose-dependent effect of sodium
ingestion on performance.
The performance outcomes measured in the included
studies also varied considerably. Notwithstanding the
differences in validity between time to exhaustion and time
trial or distance-tests [28], there was no particular effect of
the type of performance measured on whether or not
sodium intake was beneficial. The single study to show a
performance improvement did so by measuring the effect of
ingestion of sodium or placebo capsules, in a blinded
manner, on finish time of a half-IM triathlon [26]. In
contrast, the study of sodium supplementation on
performance in a full distance Ironman triathlon failed to
find a difference in performance [27]. The inclusion of
these two studies is also of interest, with advantages and
disadvantages of measuring performance during an
organized competition. Ultimately, performance during
actual endurance events is the outcome of most importance
to athletes, so it can be argued that these studies represent
ecologically valid performance measures. On the other hand,
this design introduces the possibility that performance
outcomes are influenced by factors other than the
intervention studied (e.g. sodium ingestion), reducing the
reliability of this study design [28]. As both studies that
occurred during organized competitions were triathlon
events, variables such as the time spent in transition
between legs, stopping or slowing down at aid stations,
race tactics in response to other competitors and changes
in race scenario could all conceivably influence the primary
outcome, namely event finish time. We note that the
performance improvement attributed to sodium
supplementation in the half-IM event was 7.8% [26],
a performance difference that would seem implausibly
high from a single nutritional intervention alone. In
laboratory-controlled studies measuring time trial
performance, the beneficial effects of varied CHO, fluid,
and/or caffeine ingestion are rarely greater than 5% [29-31].
Therefore, we suggest that future studies use an
ecologically valid exercise model, but do so in a more
controlled laboratory or field-based setting to improve their
Four of the five included studies were conducted
outdoors [23, 24, 26, 27]. This means that ambient
temperature, relative humidity, wind speed and direction
could vary considerably between intervention groups. In the
organized competition studies, participants competed at the
same time, taking either sodium or placebo supplementation.
Therefore conditions were not different between groups at
race start, but may have differed as event duration increased
in time. For the crossover trials however, participants
completed trials on different days. One study [24] observed
an effect of trial order, likely due to large differences in
ambient temperature between trial days. Cosgrove and
Black [23] reported no significant difference in ambient
conditions between trial days but did not report wind
conditions, other than to state the course and time of day
was chosen to minimise the influence of the wind. Cycling
time trial performance is significantly affected by wind
speed and direction, whereby even subtle changes could
conceivably have measurable effects on performance [32].
To our surprise, none of the included studies were
completed in hot ambient conditions (e.g., ≥30°C), where
any theoretical benefit of sodium ingestion on performance
would be expected to be greater, due to increased fluid and
sodium losses. Moreover, in hot ambient conditions the
total sodium losses would be expected to be greater than
temperate conditions due to increased sweating rate,
especially for individuals who are not heat acclimated [2].
Although excessive fluid intake has been identified as the
main cause of EAH in most cases, there are suggestions that
excessive sweat sodium losses even in the absence of fluid
excess can increase the risk of a hypovolaemic EAH, the
development of which, if symptomatic, would almost
certainly impair performance [13]. Ideally, studies of
sodium intake during exercise and performance would be
conducted in a laboratory setting, in both hot and temperate
ambient conditions, with careful control of all
environmental variables.
Two other major control variables when measuring
endurance exercise performance are the intake of CHO and
fluid during the exercise bout. The effect of CHO intake on
performance is well established, with increased CHO
ingestion during the exercise durations of the included
studies likely to be beneficial to performance [31]. Despite
this, only one of the included studies provided a
standardised CHO intake across intervention groups (60g/h
in low and no sodium trials, 63g/h in high sodium trial) [24],
while one of the included studies conducted during an
organized competition allowed ad libitum CHO intake and
reported no difference between groups (sodium intervention:
International Journal of Sports Science 2018, 8(3): 97-107 105
32 g/h, placebo: 40 g/h) [26]. Differences in fluid intake
between intervention groups may also be of significance to
the performance outcomes of the included studies. It is
therefore perhaps surprising that only two of the included
studies standardised fluid intake between interventions [24,
25], with the other three allowing ad libitum fluid intake [23,
26, 27]. Of the three studies where fluid intake was allowed
ad libitum, two reported actual fluid intake, and in both
cases fluid intake was significantly greater with sodium
supplementation compared to placebo [23]. Some authors
have suggested that one of the benefits of sodium ingestion
during exercise is the stimulation of thirst and subsequently
greater voluntary fluid intake and fluid retention [1].
Therefore, it could be argued that the lack of standardisation
of fluid intake represents a feature rather than a flaw in
study design. In future studies, comparison of sodium intake
with both standardised and ad libitum fluid intakes would
be helpful in understanding whether sodium has a direct
(when fluid intake is standardised) or an indirect effect (due
to stimulation of greater fluid intake) on performance in
different scenarios.
Finally, the method of sodium ingestion may also be
important in determining any performance effect. Four of
the five included studies provided sodium in capsule form.
This provides the distinct advantage of participant blinding,
since the distinctive taste of sodium chloride cannot be
detected and compared to the placebo. The use of capsules
assumes that any effect of sodium ingestion occurs from
absorption of sodium from the gastrointestinal tract, and
subsequent effects on PV, osmolality and thirst drive. Given
that there appear to be effects of both CHO and caffeine in
the oral cavity on performance, without ingestion [33, 34],
it is conceivable that there could be an independent effect of
sodium in the oral cavity that is independent of consuming
it in capsule form. Future studies may be able to examine
this relationship by comparing the consumption of sodium
capsules and solutions on endurance performance.
4.2. Mechanisms for a Potential Effect of Sodium Intake
during Endurance Exercise on Performance
Guidelines that encourage the consumption of sodium
during endurance exercise suggest two mechanisms that
could theoretically improve performance. Firstly, sodium
intake increases thirst and promotes greater voluntary fluid
consumption [1]. Secondly, sodium ingestion promotes
greater PV retention and reduces urine output [1, 6]. These
mechanisms are often cited by sports nutrition companies
commercialising sodium containing products, implying
exercise performance benefits from quantified sodium
ingestion during endurance exercise. Of the three studies
included in this review where fluid was consumed ad
libitum during exercise, two found increased fluid
consumption with sodium supplementation [23, 26], whilst
the other did not report fluid intake [27]. But despite the
theoretical rationale that increased fluid intake would
improve performance, only one of these three studies found
a performance benefit from increased sodium (and
subsequently increased fluid) intake [26]. It is possible that
the exercise duration and subsequent relative exercise
intensity required to optimise performance in these
scenarios was too long and too low respectively; such that
TBW and PV are not limiting factors on performance, or
that because the rate of sweating is less with lowered
exercise intensity, ad libitum fluid intake is adequate to
maintain PV even in the absence of sodium ingestion. Only
one of the included studies reported change in PV during
exercise, and although there was an effect of sodium
ingestion, PV in the placebo group showed a reduction of
less than 1% [23]. Studying the effect of sodium ingestion
during exercise in hot ambient conditions (e.g., ≥30°C)
would provide more insight into whether the greater
maintenance of TBW and PV with sodium ingestion
subsequently improves performance.
4.3. Sodium Ingestion during Exercise, Endurance
Performance and Current Sports Nutrition
Current sports nutrition guidelines specifically include
sodium as a key nutrient of interest, especially for
endurance athletes [1, 18]. However unlike CHO and fluid,
no specific sodium consumption recommendations are
advised, and there is minimal evidence to draw a link
between sodium ingestion and endurance performance. This
is not surprising given the findings of this systematic review,
which found only a small number of studies on the topic,
with methodologies that resulted in an unclear or high risk
of bias in all cases, and with no participant-specific sodium
intake levels used. This points to the need for more
controlled and robust research in this area, in order to better
inform sports nutrition recommendations and guidelines in
the future. Such research should include careful dietary
standardisation of both macronutrient and sodium intake in
the days prior to exercise, careful control of exercise
intensity and duration, pre-exercise hydration status, heat
acclimation status and ambient conditions [4]. In addition,
sweat sodium losses should be measured in an identical
prior exercise bout, with whole body washdown the
preferred method of sweat collection [2], and sodium
replacement provided during exercise as a proportion of the
expected losses, which can vary considerably [3].
4.4. Study Limitations
One potential limitation to this systematic review is that
other existing studies were missed during our search. We
attempted to minimise this risk by searching the reference
lists of the identified papers, and of known review papers
relevant to the topic. We were also unable to perform a
meta-analysis of the included papers, due to the large
differences in study design, particularly the exercise
performance outcome measures used.
106 Alan J. McCubbin et al.: Impact of Sodium Ingestion During
Exercise on Endurance Performance: A Systematic Review
5. Conclusions
Endurance athletes anecdotally consume sodium
containing foods, fluids, and supplements during endurance
exercise, partly in the belief that it will improve their
exercise performance. In addition, commercial sweat testing
services allow quantification of sweat sodium losses during
exercise, providing athletes with an information guide to
replace expected losses during training or competition.
However, our systematic review failed to find any studies
that examine the effect of quantified sodium replacement
according to expected losses during endurance exercise.
In addition, we found that arbitrary sodium ingestion
during endurance exercise does not improve endurance
performance compared to no sodium intake in temperate
ambient conditions, albeit that all of the identified studies
were found to have either a high or unclear risk of bias, and
participants were not impaired during exercise by either
EAMC or symptomatic EAH from either the presence or
absence of sodium intake during the exercise bout. There
are currently no studies that describe the effect of sodium
ingestion during exercise on endurance performance in hot
ambient conditions. Future research should attempt to
address these issues, with valid and reliable quantification
of sweat sodium losses to inform sodium replacement
strategies, both programmed and ad libitum fluid ingestion,
during well controlled exertional-heat stress models, whilst
ensuring adequate control of study blinding and potentially
confounding variables such as CHO intake, hydration status,
wind speed and direction.
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... However, the evidence supporting this recommendation is limited. A recent systematic review (14) found that only one of the five included studies reported a significant benefit of sodium ingestion on endurance performance. In addition, four of the five included studies were conducted outdoors (14), meaning that the findings could have been confounded by factors such as ambient temperature, relative humidity, wind speed and direction. ...
... A recent systematic review (14) found that only one of the five included studies reported a significant benefit of sodium ingestion on endurance performance. In addition, four of the five included studies were conducted outdoors (14), meaning that the findings could have been confounded by factors such as ambient temperature, relative humidity, wind speed and direction. Furthermore, it is unknown whether sodium ingestion influences tennis-specific skill, which involves a combination of physical, technical, and cognitive factors. ...
Full-text available
This study examined the dose-response effects of ingesting different sodium concentrations on markers of hydration and tennis skill. Twelve British nationally-ranked tennis players (age: 21.5 ± 3.1 years; VO 2peak : 45.5 ± 4.4 ml. kg. min −1) completed four identical indoor tennis training sessions in a cluster randomized, single-blind, placebo-controlled, crossover design. Twenty-minutes prior to each training session, participants consumed a 250 ml sodium-containing beverage (10, 20, 50 mmol/L) or a placebo (0 mmol/L), and continued to consume 1,000 ml of the same beverage at set periods during the 1-h training session. Tennis groundstroke and serve performance, agility, urine osmolality, fluid loss, sodium sweat loss and perceptual responses (rating of perceived exertion (RPE), thirst, and gastrointestinal (GI) discomfort) were assessed. Results showed that ingesting 50 mmol/L sodium reduced urine osmolality (−119 mOsmol/kg; p = 0.037) and improved groundstroke performance (5.4; p < 0.001) compared with placebo. This was associated with a reduction in RPE (−0.42; p = 0.029), perception of thirst (−0.58; p = 0.012), and GI discomfort (−0.55; p = 0.019) during the 50 mmol/L trial compared with placebo. Linear trend analysis showed that ingesting greater concentrations of sodium proportionately reduced urine osmolality (β = −147 mOsmol/kg; p = 0.007) and improved groundstroke performance (β = 5.6; p < 0.001) in a dose response manner. Perceived thirst also decreased linearly as sodium concentration increased (β = −0.51; p = 0.044). There was no evidence for an effect of sodium consumption on fluid loss, sweat sodium loss, serve or agility performance (p > 0.05). In conclusion, consuming 50 mmol/L of sodium before and during a 1-h tennis training session reduced urine osmolality and improved groundstroke performance in nationally-ranked tennis players. There was also evidence of dose response effects, showing that ingesting greater sodium concentrations resulted in greater improvements in groundstroke performance. Munson et al. Sodium Ingestion Improves Tennis Skill The enhancement in tennis skill may have resulted from an attenuation of symptomologic distracters associated with hypohydration, such as RPE, thirst and GI discomfort.
... It appears unlikely that salt intake will impact of thermoregulation or rating of perceived exertion to any significant extent, with the volume of water consumed a much more potent driver of both (Sanders et al., 2001, Baker et al., 2008. The overall impact of salt replacement during exertional heat stress on endurance performance is beyond the scope of this review, but readers are directed to a recent systematic review on the topic, that noted only a small number of poorly controlled studies, many with significant methodological issues, none of which were conducted in hot conditions, and none of J o u r n a l P r e -p r o o f which attempted to individualize the salt intake to the athlete's expected losses (McCubbin and Costa, 2018b). ...
Exertional heat stress presents a different acute challenge to salt balance compared to at rest. Sodium (Na⁺) and chloride (Cl⁻) losses during exercise are overwhelmingly driven by eccrine sweat glands (the “leader”), with minimal urinary excretion. Total salt losses are therefore largely influenced by thermoregulatory need, although adaptations from prior heat exposure or altered dietary intake influences sweat gland ion reabsorption, and therefore sweat Na⁺ ([Na⁺]sweat) and Cl⁻ concentrations. The hypotheses that body Na⁺ and Cl⁻ conservation, or their release from osmotically inactive stores, can occur during the timeframe of a single bout of exertional heat stress, has not been studied to date. The consequences of unreplaced Na⁺ and Cl⁻ losses during exertional heat stress appear limited primarily to their interactions with water balance. However, the water volume ingested is substantially more influential than salt intake on total body water, plasma volume, osmolality, and thermoregulation during exercise. Acute salt and water loading 1–3 h prior to exercise can induce isosmotic hyperhydration in situations where this is deemed beneficial. During exercise, only scenarios of whole body [Na⁺]sweat > 75th centile, combined with fluid replacement >80% of losses, are likely to require significant replacement to prevent hyponatremia. Post-exercise, natriuresis resumes as the main regulator of salt losses, with the kidneys (the “follower”) working to restore salt balance incurred from any exercise-induced deficit. If such a deficit exceeds usual dietary intake, and rapid restoration of hydration status is desirable, a deliberate increase in salt intake may assist in volume restoration.
... However, some sports nutrition guidelines encourage higher sodium ingestion during endurance exercise, and much work was done to quantify sweat sodium losses during exercise. Current guidelines for sodium intake do not recommend specific quantities, nor provide justification for the effectiveness of sodium to improve endurance performance [31]. Sodium over-consumption in the studied athletes was probably due to their dietary preferences, as they declared to frequently consume salty snacks [32]. ...
Full-text available
Windsurfing is a demanding activity that requires a high level of physical fitness as well as ap-propriate training and nutritional strategies. Therefore, the aim of this study was to assess the dietary intake of amateur windsurfers and consider possible dietary mistakes. This field study was conducted among 10 Polish male amateur windsurfers (aged 22 ± 2 years, mean training experience of 9.5 ± 4 years). Dietary intake was assessed using a standardized 3-day food record. The total energy expenditure of each participant was estimated using a mobile fitness application. The daily energy supply in assessed portions of the windsurfers’ food was lower than the estimated demand during the competition. The contribution of macronutrients to the total energy intake adhered to those guidelines, but not with the ones recommended for athletes practicing extreme sports. Daily fluid consumption was insufficient. In the windsurfers’ diet, we noticed low consumption of vitamin D and calcium, while cholesterol, sodium, potassium, and phosphorus intake was too high. Nutritional practices of amateur windsurfers during the competitive period do not comply with current sports nutrition guidelines. The results suggest that windsurfers are in need of nu-tritional education and dietary counseling in order to meet macronutrient intake targets.
... Cooler beverages (<22°C) tend to increase fluid palatability and voluntary consumption during exercise (Burdon et al., 2012), while planned consumption of cold (<10°C) or iced beverages may convey additional perceptual or performance benefits when exercise is undertaken in hot ambient conditions (Burdon et al., 2010a;Lee et al., 2008). Sodium replacement during prolonged exertional heat stress has been less rigorously studied, preventing conclusions about the value of quantifying or replacing sweat Na + losses to address issues of cramp prevention or optimal performance (McCubbin & Costa, 2018). Nevertheless, individualized protocols for electrolyte replacement may offer some benefit for specific scenarios until further research can offer a more evidence-based approach. ...
Full-text available
It is the position of Sports Dietitians Australia (SDA) that exercise in hot and/or humid environments, or with significant clothing and/or equipment that prevents body heat loss (i.e., exertional heat stress), provides significant challenges to an athlete’s nutritional status, health, and performance. Exertional heat stress, especially when prolonged, can perturb thermoregulatory, cardiovascular, and gastrointestinal systems. Heat acclimation or acclimatization provides beneficial adaptations and should be undertaken where possible. Athletes should aim to begin exercise euhydrated. Furthermore, preexercise hyperhydration may be desirable in some scenarios and can be achieved through acute sodium or glycerol loading protocols. The assessment of fluid balance during exercise, together with gastrointestinal tolerance to fluid intake, and the appropriateness of thirst responses provide valuable information to inform fluid replacement strategies that should be integrated with event fuel requirements. Such strategies should also consider fluid availability and opportunities to drink, to prevent significant under- or overconsumption during exercise. Postexercise beverage choices can be influenced by the required timeframe for return to euhydration and co-ingestion of meals and snacks. Ingested beverage temperature can influence core temperature, with cold/icy beverages of potential use before and during exertional heat stress, while use of menthol can alter thermal sensation. Practical challenges in supporting athletes in teams and traveling for competition require careful planning. Finally, specific athletic population groups have unique nutritional needs in the context of exertional heat stress (i.e., youth, endurance/ultra-endurance athletes, and para-sport athletes), and specific adjustments to nutrition strategies should be made for these population groups.
... Still, other studies have found no effect of high Na + ingestion (900 mg/h) during prolonged exercise on cardiovascular drift, skin temperature, rating of perceived exertion, or time to exhaustion (Earhart, Weiss, Rahman, & Kelly, 2015). A recent systematic review of five studies concluded that there is limited evidence to suggest that endurance performance improves with Na + ingestion and emphasized the need for further studies (McCubbin & Costa, 2018b). ...
Full-text available
The purpose of this study was to expand our previously published sweat normative data/analysis (n = 506) to establish sport-specific normative data for whole-body sweating rate (WBSR), sweat [Na⁺], and rate of sweat Na⁺ loss (RSSL). Data from 1303 athletes were compiled from observational testing (2000–2017) using a standardized absorbent sweat patch technique to determine local sweat [Na⁺] and normalized to whole-body sweat [Na⁺]. WBSR was determined from change in exercise body mass, corrected for food/fluid intake and urine/stool loss. RSSL was the product of sweat [Na⁺] and WBSR. There were significant differences between sports for WBSR, with highest losses in American football (1.51 ± 0.70 L/h), then endurance (1.28 ± 0.57 L/h), followed by basketball (0.95 ± 0.42 L/h), soccer (0.94 ± 0.38 L/h) and baseball (0.83 ± 0.34 L/h). For RSSL, American football (55.9 ± 36.8 mmol/h) and endurance (51.7 ± 27.8 mmol/h) were greater than soccer (34.6 ± 19.2 mmol/h), basketball (34.5 ± 21.2 mmol/h), and baseball (27.2 ± 14.7 mmol/h). After ANCOVA, significant between-sport differences in adjusted means for WBSR and RSSL remained. In summary, due to the significant sport-specific variation in WBSR and RSSL, American football and endurance have the greatest need for deliberate hydration strategies. Abbreviations: WBSR: whole body sweating rate; SR: sweating rate; Na⁺: sodium; RSSL: rate of sweat sodium loss
... As well as fluid intake, it is a common practice for athletes to supplement with sodium, before and during exercise [107][108][109]. Anecdotally, one rationale for sodium supplementation is the focus and belief on attenuating dehydration, and subsequently reducing occurrence and severity of GIS. ...
Exercise-induced gastrointestinal syndrome (EIGS) is a common characteristic of exercise. The causes appear to be multi-factorial in origin, but stem primarily from splanchnic hypoperfusion and increased sympathetic drive. These primary causes can lead to secondary outcomes that include increased intestinal epithelial injury and gastrointestinal hyperpermeability, systemic endotoxaemia and responsive cytokinaemia, and impaired gastrointestinal function (i.e., transit, digestion and absorption). Impaired gastrointestinal integrity and functional responses may predispose individuals, engaged in strenuous exercise, to gastrointestinal symptoms (GIS) and health complications of clinical significance, both of which may have exercise performance implications. There is a growing body of evidence indicating heat exposure during exercise (i.e., exertional-heat stress) can substantially exacerbate these gastrointestinal perturbations, proportionally to the magnitude of exertional-heat stress, which is of major concern for athletes preparing for and competing in the upcoming 2020 Tokyo Olympic Games. To date, various hydration and nutritional strategies have been explored to prevent or ameliorate exertional-heat stress associated gastrointestinal perturbations. The aims of the current review are to comprehensively explore the impact of exertional-heat stress on markers of EIGS, examine the evidence for the prevention and (or) management of EIGS in relation to exertional-heat stress, and establish best-practice nutritional recommendations for athletes preparing for and competing in Tokyo 2020.
... Despite this theoretical rationale, evidence that sodium replacement during exercise improves performance is scarce. A recent systematic literature review found minimal evidence of performance benefits from sodium intake during exercise (2-13 hr duration), although it was noted the quality of existing studies was poor (McCubbin & Costa, 2018a). In contrast, preexercise sodium loading (1,500-3,000 mg ingested 15-45 min prior to exercise stress) appears beneficial to performance during 1-2 hr exercise durations due to expanded plasma volume, resulting in improved thermoregulation (Coles & Luetkemeier, 2005;Sims et al., 2007). ...
There is little information describing how endurance athletes perceive sodium intake in relation to training and competition. Using an online questionnaire, this study assessed the beliefs, information sources, and intended practices regarding sodium ingestion for training and competition. Endurance athletes (n = 344) from six English-speaking countries completed the questionnaire and were included for analysis. The most cited information sources were social supports (63%), self-experimentation (56%), and media (48%). Respondents generally believed (>50% on electronic visual analog scale) endurance athletes require additional sodium on a daily basis (median 67% [interquartile range: 40-81%]), benefit from increased sodium in the days preceding competition (60% [30-77%]), should replace sodium losses during training (69% [48-83%]) and competition (74% [54-87%]), and would benefit from sweat composition testing (82% [65-95%]). Respondents generally believed sodium ingestion during endurance exercise prevents exercise-associated muscle cramps (75% [60-88%]) and exercise-associated hyponatremia (74% [62-89%]). The majority (58%) planned to consciously increase sodium or total food intake (i.e., indirectly increasing sodium intake) in the days preceding competition. Most (79%) were conscious of sodium intake during competition, but only 29% could articulate a specific intake plan. A small minority (5%) reported using commercial sweat testing services, of which 75% believed it was beneficial. We conclude that endurance athletes commonly perceive sodium intake as important for their sporting activities. Many intend to consciously increase sodium intake in the days preceding and during competition, although these views appear informed mostly by nonscientific and/or non-evidence-based sources.
Ultramarathon running events and participation numbers have increased progressively over the past three decades. Besides the exertion of prolonged running with or without a loaded pack, such events are often associated with challenging topography, environmental conditions, acute transient lifestyle discomforts, and/or event-related health complications. These factors create a scenario for greater nutritional needs, while predisposing ultramarathon runners to multiple nutritional intake barriers. The current review aims to explore the physiological and nutritional demands of ultramarathon running and provide general guidance on nutritional requirements for ultramarathon training and competition, including aspects of race nutrition logistics. Research outcomes suggest that daily dietary carbohydrates (up to 12 g·kg-1·day-1) and multiple-transportable carbohydrate intake (∼90 g·hr-1 for running distances ≥3 hr) during exercise support endurance training adaptations and enhance real-time endurance performance. Whether these intake rates are tolerable during ultramarathon competition is questionable from a practical and gastrointestinal perspective. Dietary protocols, such as glycogen manipulation or low-carbohydrate high-fat diets, are currently popular among ultramarathon runners. Despite the latter dietary manipulation showing increased total fat oxidation rates during submaximal exercise, the role in enhancing ultramarathon running performance is currently not supported. Ultramarathon runners may develop varying degrees of both hypohydration and hyperhydration (with accompanying exercise-associated hyponatremia), dependent on event duration, and environmental conditions. To avoid these two extremes, euhydration can generally be maintained through "drinking to thirst." A well practiced and individualized nutrition strategy is required to optimize training and competition performance in ultramarathon running events, whether they are single stage or multistage.
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There has been recent interest in the ergogenic effects of caffeine delivered in low doses (~ 200 mg or ~ 3 mg/kg body mass) and administered in forms other than capsules, coffee and sports drinks, including chewing gum, bars, gels, mouth rinses, energy drinks and aerosols. Caffeinated chewing gum is absorbed quicker through the buccal mucosa compared with capsule delivery and absorption in the gut, although total caffeine absorption over time is not different. Rapid absorption may be important in many sporting situations. Caffeinated chewing gum improved endurance cycling performance, and there is limited evidence that repeated sprint cycling and power production may also be improved. Mouth rinsing with caffeine may stimulate nerves with direct links to the brain, in addition to caffeine absorption in the mouth. However, caffeine mouth rinsing has not been shown to have significant effects on cognitive performance. Delivering caffeine with mouth rinsing improved short-duration, high-intensity, repeated sprinting in normal and depleted glycogen states, while the majority of the literature indicates no ergogenic effect on aerobic exercise performance, and resistance exercise has not been adequately studied. Studies with caffeinated energy drinks have generally not examined the individual effects of caffeine on performance, making conclusions about this form of caffeine delivery impossible. Caffeinated aerosol mouth and nasal sprays may stimulate nerves with direct brain connections and enter the blood via mucosal and pulmonary absorption, although little support exists for caffeine delivered in this manner. Overall, more research is needed examining alternate forms of caffeine delivery including direct measures of brain activation and entry of caffeine into the blood, as well as more studies examining trained athletes and female subjects.
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The B-722 Laqua Twin is a low cost, portable and battery operated sodium analyser, which can be used for the assessment of sweat sodium concentration. The Laqua Twin is reliable and provides a degree of accuracy similar to more expensive analysers; however, its inter-unit measurement error remains unknown. The purpose of this study was to compare the sodium concentration values of 70 sweat samples measured using three different Laqua Twin units. Mean absolute errors, random errors and constant errors among the different Laqua Twins ranged respectively between 1.7 mmol/L to 3.5 mmol/L, 2.5 mmol/L to 3.7 mmol/L and -0.6 mmol/L to 3.9 mmol/L. Proportional errors among Laqua Twins were all < 2%. Based on a within-subject biological variability in sweat sodium concentration of ± 12%, the maximal allowable imprecision among instruments was considered to be ≤ 6%. In that respect, the within (2.9%), between (4.5%) and total (5.4%) measurement error coefficient of variations were all < 6%. For a given sweat sodium concentration value, the largest observed difference in mean and lower and upper bound error of measurements among instruments were respectively of 4.7 mmol/L, 2.3 mmol/L and 7.0 mmol/L. In conclusion, our findings show that the inter-unit measurement error of the B-722 Laqua Twin is low and methodologically acceptable.
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Purpose: Sweat sodium concentration (SSC) can be determined using different analytical techniques (ATs), which may have implications for athletes and scientists. This study compared the SSC measured with five ATs: ion chromatography (IChr), flame photometry (FP), direct (DISE) and indirect (IISE) ion selective electrode and ion conductivity (IC). Methods: Seventy sweat samples collected from 14 athletes were analyzed with 5 instruments: the 883 Basic IC Plus (IChr, reference instrument), AAnalyst 200 (FP), Cobas 6000 (IISE), Sweat-Chek (IC) and B-722 Laqua Twin (DISE). Results: Instruments showed excellent relative (Intraclass correlation coefficient (ICC) ≥ 0.999) and absolute (Coefficient of variation (CV) ≤ 2.6%) reliability. Relative validity was also excellent between ATs (ICC ≥ 0.961). In regards to the inter-AT absolute validity, compared with IChr, standard error of the estimates (SEEs) were similar among ATs (2.8-3.8 mmol/L), but CV was lowest with DISE (3.9%), intermediate with IISE (7.6%) and FP (6.9%) and highest with IC (12.3%). Conclusions: SSC varies depending on the AT used to analyse samples. Therefore, results obtained from different ATs are scarcely comparable and should not be used interchangeably. Nevertheless, taking into account the normal variability in SSC (~± 12%), the imprecision of the recommendations deriving from FP, IISE, IC and DISE should have trivial health and physiological consequences under most exercise circumstances.
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Athletes lose water and electrolytes as a consequence of thermoregulatory sweating during exercise and it is well known that the rate and composition of sweat loss can vary considerably within and among individuals. Many scientists and practitioners conduct sweat tests to determine sweat water and electrolyte losses of athletes during practice and competition. The information gleaned from sweat testing is often used to guide personalized fluid and electrolyte replacement recommendations for athletes; however, unstandardized methodological practices and challenging field conditions can produce inconsistent/inaccurate results. The primary objective of this paper is to provide a review of the literature regarding the effect of laboratory and field sweat-testing methodological variations on sweating rate (SR) and sweat composition (primarily sodium concentration [Na+]). The simplest and most accurate method to assess whole-body SR is via changes in body mass during exercise; however, potential confounding factors to consider are non-sweat sources of mass change and trapped sweat in clothing. In addition, variability in sweat [Na+] can result from differences in the type of collection system used (whole body or localized), the timing/duration of sweat collection, skin cleaning procedure, sample storage/handling, and analytical technique. Another aim of this paper is to briefly review factors that may impact intra/interindividual variability in SR and sweat [Na+] during exercise, including exercise intensity, environmental conditions, heat acclimation, aerobic capacity, body size/composition, wearing of protective equipment, sex, maturation, aging, diet, and/or hydration status. In summary, sweat testing can be a useful tool to estimate athletes’ SR and sweat Na+ loss to help guide fluid/electrolyte replacement strategies, provided that data are collected, analyzed, and interpreted appropriately.
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The present study aimed to assess the adequacy of energy, macronutrients and water intakes of ultra-endurance runners (UER) competing in a 24 h ultra-marathon (distance range: 122-208 km). The ad libitum food and fluid intakes of the UER (n 25) were recorded throughout the competition and analysed using dietary analysis software. Body mass (BM), urinary ketone presence, plasma osmolality (POsmol) and volume change were determined at pre- and post-competition time points. Data were analysed using appropriate t tests, with significance set at P <0·05. The total energy intake and expenditure of the UER were 20 (sd 12) and 55 (sd 11) MJ, respectively (control (CON) (n 17): 12 (sd 1) and 14 (sd 5) MJ, respectively). The protein, carbohydrate and fat intakes of the UER were 1·1 (sd 0·4), 11·3 (sd 7·0) and 1·5 (sd 0·7) g/kg BM, respectively. The rate of carbohydrate intake during the competition was 37 (sd 24) g/h. The total water intake of the UER was 9·1 (sd 4·0) litres (CON: 2·1 (sd 1·0) litres), while the rate of water intake was 378 (sd 164) ml/h. Significant BM loss occurred at pre- to post-competition time points (P =0·001) in the UER (1·6 (sd 2·0) %). No significant changes in POsmol values were observed at pre- (285 (sd 11) mOsmol/kg) to post-competition (287 (sd 10) mOsmol/kg) time points in the UER and were lower than those recorded in the CON group (P <0·05). However, plasma volume (PV) increased at post-competition time points in the UER (10·2 (sd 9·7) %; P <0·001). Urinary ketones were evident in the post-competition samples of 90 % of the UER. Energy deficit was observed in all the UER, with only one UER achieving the benchmark recommendations for carbohydrate intake during endurance exercise. Despite the relatively low water intake rates recorded in the UER, hypohydration does not appear to be an issue, considering increases in PV values observed in the majority (80 %) of the UER. Population-specific dietary recommendations may be beneficial and warranted.
Purpose: The aim of the present study was to examine the effect of dehydration on exercise performance independently of thirst with subjects blinded of their hydration status. Methods: Seven male cyclists (weight: 72±9 kg, body fat: 14±6%, VO2peak: 59.4±6 ml[BULLET OPERATOR]kg·min) exercised for 2 hours on a cycle ergometer at 55% VO2peak, in a hot-dry environment (35°C, 30% rh), with a nasogastric (NG) tube under euhydrated - non-thirst (EUH-NT) and dehydrated - non-thirst (DEH-NT) conditions. In both trials, thirst was matched by drinking 25 mL of water every 5-min (300 mL[BULLET OPERATOR]h). In the EUH-NT trial sweat losses were fully replaced by water via the NG tube (calculated from the familiarization trial). Following the 2-h of steady state, the subjects completed a 5-km cycling time trial at 4% grade. Results: Body mass loss for the EUH-NT and DEH-NT after the 2-h was -0.2±0.6 and -2.2±0.4%, while after the 5-km time trial was -0.7±0.5 and 2.9±0.4%, respectively. Thirst (35±30 vs. 42±31 mm) and stomach fullness (46±21 vs. 35±20 mm) did not differ at the end of the 2-h of steady state between EUH-NT and DEH-NT trials (P>0.05). Subjects cycled faster during the 5-km time trial in the EUH-NT trial compared to the DEH-NT trial (23.2±1.5 vs. 22.3±1.8 km·h, P<0.05), by producing higher power output (295±29 vs. 276±29 W, P<0.05). During the 5-km time trial, core temperature was higher in the DEH-NT trial (39.2±0.7 °C) compared to the EUH-NT trial (38.8±0.2°C; P>0.05). Conclusion: These data indicated that hypohydration decreased cycling performance and impaired thermoregulation independently of thirst, while the subjects were unaware of their hydration status.
The collection, processing, and analysis of sweat samples to determine sodium losses during endurance exercise is common amongst sports and exercise nutrition practitioners, and necessary for researchers investigating sodium losses and replacement strategies. Several factors influence sweat sodium concentration ([Na+]) that need to be controlled or considered when interpreting results. Dietary sodium intake in the days preceding exercise is one factor that may influence sweat [Na+]. A systematic review was undertaking using six databases (CINAHL, Embase, Medline Ovid, Scopus, SPORTDiscus, and Web of Science) to determine the impact of dietary sodium intake on sweat [Na+] in response to endurance exercise. Six papers met the inclusion criteria. They varied in the level of sodium intake (<196 to 9177 mg/d), intervention timeframe (3 to 42 days), exercise modality (cycling ergometry, treadmill walking and running), and sweat collection method (whole body washdown and regional patch techniques). Two studies showed significant differences in sweat [Na+] due to diet, two showed no significant difference, and two were not analysed statistically. No relationship was found across studies comparing the difference in sodium intake between interventions and sweat [Na+]. Several limitations were identified, including lack of validation of the intervention, collecting regional sweat samples from limited sites or averaging results across sites or collection days, and lack of statistical analysis. It is concluded that the impact of dietary sodium intake on sweat [Na+] in response to endurance exercise remains uncertain, however the review provides useful insights into the optimal study design for future research in this area.
The purpose of this study was to establish normative data for regional sweat sodium concentration ([Na(+)]) and whole-body sweating rate in athletes. Data from 506 athletes (367 adults, 139 youth; 404 male, 102 female) were compiled from observational athlete testing for a retrospective analysis. The participants were skill/team-sport (including American football, baseball, basketball, soccer and tennis) and endurance (including cycling, running and triathlon) athletes exercising in cool to hot environmental conditions (15-50°C) during training or competition in the laboratory or field. A standardised regional absorbent patch technique was used to determine sweat [Na(+)] on the dorsal mid-forearm. Whole-body sweat [Na(+)] was predicted using a published regression equation (y = 0.57x+11.05). Whole-body sweating rate was calculated from pre- to post-exercise change in body mass, corrected for fluid/food intake (ad libitum) and urine output. Data are expressed as mean ± SD (range). Forearm sweat [Na(+)] and predicted whole-body sweat [Na(+)] were 43.6 ± 18.2 (12.6-104.8) mmol · L(-1) and 35.9 ± 10.4 (18.2-70.8) mmol · L(-1), respectively. Absolute and relative whole-body sweating rates were 1.21 ± 0.68 (0.26-5.73) L · h(-1) and 15.3 ± 6.8 (3.3-69.7) ml · kg(-1) · h(-1), respectively. This retrospective analysis provides normative data for athletes' forearm and predicted whole-body sweat [Na(+)] as well as absolute and relative whole-body sweating rate across a range of sports and environmental conditions.
Guidelines recommend the consumption of sodium during exercise to replace losses in sweat; however, the effects of sodium on thermoregulation are less clear. To determine the effects of high-dose sodium supplementation on indices of thermoregulation and related outcomes, 11 endurance athletes participated in a double-blind, randomized-sequence, crossover study in which they underwent 2-hrs of endurance exercise at 60% heart rate reserve with 1800 mg of sodium supplementation (SS) during one trial and placebo (PL) during the other trial. A progressive intensity time-to-exhaustion test was performed after the 2-hr steady state exercise as an assessment of exercise performance. Sweat rate was calculated from changes in body weight, accounting for fluid intake and urinary losses. Ratings of perceived exertion (RPE) and heat stress were assessed using verbal numeric scales. Cardiovascular drift was determined from the rise in HR during the 2-hr steady state exercise test. Skin temperature was measured with an infrared thermometer. Dehydration occurred in both SS and PL trials, as evidenced by substantial weight loss (2.03 ± 0.43% and 2.27 ± 0.70%, respectively; p = 0.261 between trials). Sweat rate was 1015.53 ± 239.10 ml·hr(-1) during the SS trial and 1053.60±278.24 ml/hr during the PL trial, with no difference between trials (p = 0.459). Heat stress ratings indicated moderate heat stress ("warm/hot" ratings) but were not different between trials (p = 0.825). Time to exhaustion during the SS trial was 6.88 ± 3.88 minutes and during the PL trial averaged 6.96 ± 3.61 minutes, but did not differ between trials (p = 0.919). Cardiovascular drift, skin temperature, and RPE did not differ between trials (all p > 0.05). High-dose sodium supplementation does not appear to impact thermoregulation, cardiovascular drift, or physical performance in trained, endurance athletes. However, in light of the possibility that high sodium intakes might have other adverse effects, such as hypertension, it is our recommendation that athletes interpret professional recommendations for sodium needs during exercise with caution. Key pointsBased on current professional recommendations to replace sodium losses in sweat during exercise, some endurance athletes consume salt or other electrolyte supplements containing sodium during training and competition, however the effects of sodium on thermoregulation are less clear.High-dose sodium supplementation does not appear to impact thermoregulation, cardiovascular drift, or physical performance in trained, endurance athletes.The possibility remains that high sodium intakes might have other adverse effects. It is our recommendation that athletes interpret professional recommendations for sodium needs during exercise with caution.
The aim of this study was to investigate the effectiveness of oral salt supplementation to improve exercise performance during a half-ironman triathlon. Twenty-six experienced triathletes were matched for age, anthropometric data, and training status, and randomly placed into the salt group (113 mmol Na(+) and 112 mmol Cl(-) ) or the control group (cellulose). The experimental treatments were ingested before and during a real half-ironman triathlon competition. Pre- and post-race body mass, maximal force during a whole-body isometric strength test, maximal height during a countermovement jump, were measured, and blood samples were obtained. Sweat samples were obtained during the running section. Total race time was lower in the salt group than in the control group (P = 0.04). After the race, whole-body isometric strength (P = 0.17) and jump height (P = 0.49) were similarly reduced in both groups. Sweat loss (P = 0.98) and sweat Na(+) concentration (P = 0.72) were similar between groups. However, body mass tended to be less reduced in the salt group than in the control group (P = 0.09) while post-race serum Na(+) (P = 0.03) and Cl(-) (P = 0.03) concentrations were higher in the salt group than in the control group. Oral salt supplementation was effective to lessen body mass loss and increase serum electrolyte concentration during a real half-ironman. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.