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Salt and Fluid Loading: Effects on Blood Volume and Exercise Performance


Abstract and Figures

During prolonged exercise, fluid and salt losses through sweating reduce plasma volume which leads to heart rate drift in association with hyperthermia and reductions in performance. Oral rehydration with water reduces the loss of plasma volume and lessens heart rate drift and hyperthermia. Moreover, the inclusion of sodium in the rehydration solution to levels that double those in sweat (i.e., around 90 mmol/l Na(+)) restores plasma volume when ingested during exercise, and expands plasma volume if ingested pre-exercise. Pre-exercise salt and fluid ingestion with the intention of expanding plasma volume has received an increasing amount of attention in the literature in recent years. In four studies, pre-exercise salt and fluid ingestion improved performance, measured as time to exhaustion, either during exercise in a thermoneutral or in a hot environment. While in a hot environment, the performance improvements were linked to lowering of core temperatures and heart rate, the reasons for the improved performance in a thermoneutral environment remain unclear. However, when ingesting pre-exercise saline solutions above 0.9% (i.e., > 164 mmol/l Na(+)), osmolality and plasma sodium increase and core temperature remain at dehydration levels. Thus, too much salt counteracts the beneficial effects of plasma volume expansion on heat dissipation and hence in performance. In summary, the available literature suggests that pre-exercise saline ingestion with concentrations not over 164 mmol/l Na(+) is an ergogenic aid for subsequent prolonged exercise in a warm or thermoneutral environment.
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Hydration and Fluid Balance
Lamprecht M (ed): Acute Topics in Sport Nutrition.
Med Sport Sci. Basel, Karger, 2013, vol 59, pp 113–119
Salt and Fluid Loading: Effects on Blood
Volume and Exercise Performance
Ricardo Mora- Rodriguez Nassim Hamouti
University of Castilla- La Mancha, Exercise Physiology Laboratory, Toledo, Spain
During prolonged exercise, fluid and salt losses through sweating reduce plasma volume which
leads to heart rate drift, hyperthermia and reductions in performance. Oral rehydration with water
reduces the loss of plasma volume and lessens heart rate drift and hyperthermia. Moreover, the
inclusion of sodium in the rehydration solution to levels higher than those in sweat, restores
plasma volume when ingested during exercise (e.g. 100 mmol/l Na+), and expands plasma volume
if ingested pre- exercise (e.g. 164 mmol/l Na+). Pre- exercise salt and fluid ingestion with the inten-
tion of expanding plasma volume has received an increasing amount of attention in the literature
in recent years. In four studies, pre- exercise salt and fluid ingestion improved performance, mea-
sured as time to exhaustion, either during exercise in a hot or thermoneutral environment. While
in a hot environment, the performance improvements were linked to lowering of core tempera-
tures and heart rate, the reasons for the improved performance in a thermoneutral environment
remain unclear. However, when using pre- exercise saline concentrations above 0.9% (i.e. >164
mmol/l Na+), osmolality and plasma sodium increase and core temperature remain at dehydration
levels. Thus, too much salt counteracts the beneficial effects of plasma volume expansion on heat
dissipation and hence in performance. In summary, the available literature suggests that pre-
exercise saline ingestion with concentrations not over 164 mmol/l Na+ is an ergogenic aid for sub-
sequent prolonged exercise in a warm or thermoneutral environment.
Copyright © 2012 S. Karger AG, Basel
While the importance of water replenishment during and after prolonged exercise
is commonly accepted, the need of salt replacement is debatable. Sodium in blood
exerts osmotic forces that defend plasma volume during prolonged exercise induc-
ing dehydration. One of the prominent adaptations to chronic exercise in a hot cli-
mate (i.e. acclimation) is to reduce sodium excretion in sweat [1]. By doing so, more
sodium is kept in the blood, increasing osmotic forces that help to maintain blood
volume during progressive dehydration. The role of sodium in blood volume mainte-
nance is masterly illustrated in a recent experiment comparing cystic fibrosis patients
who excrete a lot of sodium in sweat (133 mmol/l) with control subjects with average
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114 Mora- Rodriguez · Hamouti
sweat sodium of 44 mmol/l [2]. Both groups exercised in a hot environment to 3%
dehydration. Due to their large sweat Na+ losses, the patients finished the exercise
with a lower blood sodium concentration than the controls (146 vs. 150 mmol/l).
With less sodium in blood to exert osmotic forces, the cystic fibrosis group had larger
plasma volume reductions during exercise than control subjects.
While curtailing sodium losses could benefit the cardiovascular system by reduc-
ing blood volume losses, adding sodium to the blood holds the promise to maintain
blood volume during prolonged exercise. This is the main focus of this review. We
will present current information about the acute use of water and salt as a nutritional
aid that can help cardiovascular function. The impact of salt and water loading on
reducing cardiovascular and thermal strain and its consequences in exercise perfor-
mance will also be discussed. Most of the review will deal with oral ingestion although
intravenous delivery of saline solutions is also presented with the aim of clarifying
the physiological mechanisms. Human sweat during exercise contains ~45 mmol/l
of Na+. Thus, studies using drinks with sodium concentrations below that range of
concentrations (i.e. sports drinks) are not considered salt loading and are beyond the
scope of this review. Lastly, we focused on studies in a normotensive population with
normal renal function and appropriate ADH secretion. Salt and water loading is obvi-
ously discouraged in hypertensive populations.
Saline Delivery after Dehydration but prior to a Subsequent Exercise Bout
Fortney et al. [3] rehydrated with saline subjects that had lost 200 ml of their plasma
volume after exercise in the heat combined with water restriction. They used intra-
venous (IV) infusion of 3% saline (0.4 ml/kg body mass/min) to successfully restore
plasma volume. However, due to the high osmolality of the infusate (i.e. 1,026 mosm/
kg H2O), plasma osmolality remained at dehydrated values and thermoregulation
did not benefit from intravascular rehydration. A series of studies have followed
(reviewed by van Rosendal et al. [4]), using isotonic (0.9%; ~308 mosm/kg H2O) or
hypotonic (0.45%; ~154 mosm/kg H2O) IV saline infusion to rehydrate subjects that
have lost fluid during prolonged exercise in the heat. In general, these IV saline solu-
tions restored plasma volume to euhydrated conditions without differences between
the iso- and hypotonic saline [5]. The acute expansion of blood volume with the IV
saline infusion seemed to restore central venous pressure improving heat dissipation.
In fact, in these studies, core temperature was lower during subsequent exercise than
when subjects did not receive saline infusions.
The main goal of the above- cited studies was to compare the rehydration effects of
IV vs. oral solutions and thus 0.45% saline solutions were also ingested. The main con-
clusion of these studies is that although IV rehydration seemed to be faster at restor-
ing plasma volume, the cardiovascular, thermoregulatory and performance benefits
during subsequent exercise were similar to when rehydrating orally [4]. While the
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Saline Ingestion Improves Performance 115
mode of delivery of the saline (IV vs. oral) was nicely addressed in these studies, no
conclusions can be derived about the effects of adding salt to a rehydration fluid since
a water ingestion control trial was not included.
Saline Delivery during Dehydrating Exercise
We found three articles investigating the role of IV saline infusion delivered during
a dehydrating exercise on the cardiovascular, thermoregulatory and performance
responses to exercise. In two of them, saline was infused while pedaling in a hot envi-
ronment (30°C) while the other study was held in a thermoneutral environment but
at higher workload (i.e. 84 vs. 60–65% V2 max) and thus all of them caused moderate
levels of heat accumulation. The three studies coincided in that infusion of isotonic
saline (0.9%; 0.3–0.9 ml/kg body weight/min) during exercise restored plasma vol-
ume to pre- exercise levels [6–8]. The infusions suppressed the gradual drift in heart
rate and reduced the hyperthermia observed when no fluid was delivered. IV infu-
sion of isotonic saline neither raised plasma sodium [6] nor blood osmolality [7].
Interestingly, performance measured by endurance time was not improved by the IV
saline infusion [6]. However, there was a wide spread of times to fatigue (8–42 min)
among the subjects participating in that study which together with the low reliability
of time to exhaustion to measure performance makes those results inconclusive.
We found three studies using saline ingestion during dehydrating exercise. In one
study [9], subjects ingested slightly hypertonic saline (1%; ~342 mosm/kg H2O) as a
rehydration fluid prior to and during exercise avoiding dehydration (i.e. <0.5% body
weight loss). The ingestion of saline raised blood osmolality to the levels of when
no fluid was ingested (i.e. dehydration trial). However, saline ingestion maintained
plasma volume at pre- exercise levels, well above the dehydration trial and somewhat
above the water ingestion trial. Despite this positive cardiovascular effect of saline
ingestion, aural temperature increased above the water trial to levels similar to the
dehydration trial. Similar to what happened with hypertonic IV saline infusions [3],
the ingestion of hypertonic saline negated the thermoregulatory benefits that may
bring about the expansion of plasma volume.
Finally, in two experiments by Sanders et al. [10, 11], subjects ingested a 400- ml
saline bolus before exercise and 100- and 150- ml aliquots every 10 min during 3–4 h
exercise at 55–65% of V2 max. In one study held in a 32°C environment [10], the fluid
ingested only replaced 50% of the fluid losses and there was no difference between
ingesting water or a saline solution of 100 mmol Na+ (~0.58% saline). For instance,
plasma volume and even plasma sodium concentration were equally maintained with
water than with the saline ingestion and heart rate drift was similarly attenuated. The
low sodium dose and volume ingested was possibly not enough to act as a plasma
volume expander. In their second experiment, fluid intake matched sweat losses dur-
ing prolonged exercise in a themoneutral environment (i.e. 20°C). On this occasion,
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116 Mora- Rodriguez · Hamouti
the ingestion of a 100- mmol/l Na+ solution maintained plasma volume (i.e. extracel-
lular fluid) better than when ingesting a 5- mmol/l Na+ solution. This was achieved by
increased fluid retention with reduced urine production that however did not affect
the heart rate drift or increase in rectal temperature. Due to the low exercise intensity
and environmental heat stress, heart rate drifted only 6% during 4 h of pedaling and
rectal temperature 1.8°C from the 15- min value [11]. It is possible that in a hotter
environment the effects of saline ingestion may have been revealed.
Saline Delivery Pre- Exercise: Effects on Plasma Volume
Greenleaf et al. [12] investigated the optimal composition of sodium beverages for
increasing plasma volume prior to exercise in euhydrated individuals. Using a com-
bination of sodium chloride and sodium citrate, they delivered drinks containing 55
mmol/l of Na+, however hypertonic (i.e. 365 mosm•kg–1 H2O) and 164 mmol•l–1 of
Na+ but hypotonic (i.e. 253 mosm•kg–1 H2O). After a drinking and resting period
(i.e. ~100 min), they found that the higher the sodium concentration, the higher the
increase in plasma volume (i.e. 5 vs. 8%, respectively). They concluded that drink-
ing a Na+ concentration appears to be more important than its osmolality to expand
plasma volume. These results were then confirmed by the same research group in
another study using a similar drink formulation [13].
Since then, other investigators have used oral saline solutions of 164 mmol/l of
Na+ to induce pre- exercise hypervolemia and to study its effects in performance dur-
ing subsequent exercise under different environmental conditions [14–17]. Unlike
Greenleaf et al. [12], these authors found lower levels of plasma volume expansion (i.e.
3–4.5% above resting values) despite ingesting a similar Na+ solution of 164 mmol/l.
We have recently found a similar low level of plasma volume expansion after inges-
tion of 10 ml/kg body mass of 164 mmol/l Na+ solution (1% expansion; Hamouti et
al., unpubl. data). This disparity in the level of plasma volume expansion between
Greenleaf et al. and other authors may possibly be due to a lower aerobic fitness level
among participants they recruited (V2 max 40 vs. 55 ml O2/kg/min in the other stud-
ies). Aerobically fit subjects are hypervolemic as a consequence of endurance training
adaptations [18]. It is then possible that training reduces the amount of plasma vol-
ume available to be expanded since they are close to the ceiling for expansion. Figure
1 depicts what level of plasma expansion could be expected when ingesting saline
solutions with regard to the aerobic fitness level of the subject.
Saline Delivery Pre- Exercise: Effects on Performance
We could find only two studies in a thermoneutral environment that report the
effects of pre- exercise saline ingestion on exercise performance. Greenleaf et al. [13]
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Saline Ingestion Improves Performance 117
found that, compared with a moderate sodium beverage (i.e. 55 mmol/l of Na+), pre-
exercise ingestion of 164 mmol/l Na+ improved cycling time to exhaustion by 24%.
However, this improvement was not associated with changes in the cardiovascular
(i.e. heart rate) or thermoregulatory responses (i.e. core temperature or total whole
body sweat rate) regardless of higher blood availability. Coles and Luetkemeier [14]
found an 8% improvement in time- trial performance upon a 3% pre- exercise blood
volume expansion with a 164- mmol/l Na+ drink compared to a non- sodium placebo
drink. Similar to Greenleaf et al. [12, 13], they did not find differences in heart rate,
core temperature, rate of perceived exertion or total body sweat rate. It is then intrigu-
ing what could have caused the improvements in performance. It is possible that the
increased plasma volume may have permitted an increase in V2 max and thus in time
to exhaustion [19]. Supporting this possibility, Coles and Luetkemeier [14] reported
that the individuals with the lower maximal aerobic fitness level (and probably lower
initial blood volume) had the greatest increase in performance upon plasma volume
expansion with saline ingestion.
In a hot environment, only two studies report performance results after pre- exercise
saline ingestion [15, 16]. There is one other study on the heat using saline ingestion to
expand plasma volume, but performance is not reported [17]. In agreement with the
thermoneutral studies just discussed, performance time to exhaustion was improved
by 22% after the ingestion of a 164- mmol/l Na+ versus a 10- mmol/l Na+ solution.
These rather large improvements in performance occurred despite moderate pre-
exercise plasma volume expansion (i.e. 4.5% [15, 16]). In the case of exercise in the
heat, the performance effects could be related to the lower core temperature and per-
ceived exertion associated with the increased plasma volume. We have recently found
similar findings during a cycling time trial under hot environmental conditions (i.e.
Pre-exercise plasma volume
expansion (% from baseline)
20 40 60 80 100 120 140 160 180
Na+ concentration in beverage (mmol·l–1)
Untrained; r = 0.98
Trained; r = 0.87
Fig. 1. Relationship between sodium concentration in the beverages from several studies and the
percent of pre- exercise plasma volume expansion. Data is separated in untrained (VO2 max 40 ml O2/
kg/min) and trained individuals (VO2 max 55 ml O2/kg/min). Each point represents one experimental
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118 Mora- Rodriguez · Hamouti
7.4% improved performance with a 1% plasma volume expansion; Hamouti et al.
unpubl. data).
From the available data using pre- exercise saline ingestion it can be concluded that,
independently of the environment in which the studies were performed, the level of
pre- exercise plasma volume expansion seems to play an important role in endurance
performance. In figure 2, we show available data which suggest that the higher the
pre- exercise plasma volume expansion, the higher the increase in endurance perfor-
mance. Again, a large plasma volume expansion is only possible in subjects with a low
aerobic fitness level and thus the ergogenic power of pre- exercise saline ingestion for
a trained athlete may not exceed 8% in a thermoneutral environment and somewhat
higher in a hot environment.
Disclosure Statement
The authors have no conflicts of interest to disclose.
Increase in performance
(% from control trial)
Pre-exercise plasma volume expasion
(% from baseline)
Cloes and Luetkemeier (2005)
Sims et al. (2007) Greenleaf et al. (1997)
r = 0.84
Hamouti et al.
(unpubl. data)
Fig. 2. Relationship between the percent of pre- exercise plasma volume expansion induced by the
ingestion of 164 mmol/l Na+ solution (10 ml/kg body mass) and the percent of increase in perfor-
mance with respect to the control trial being the ingestion of the same volume of a low sodium
solution or plain water. Each point represents one study.
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Saline Ingestion Improves Performance 119
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Ricardo Mora- Rodriguez
University of Castilla- La Mancha
Avda Carlos III, s/n, ES–45071 Toledo (Spain)
Tel. +34 925 26 88 00, ext. 5510
E- Mail
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... The ergogenic effects of these substances are considered to be based mainly on their property of increasing extracellular buffer capacity, which facilitates efflux of hydrogen ions (H + ) from contracting muscle cells [4][5][6], thereby delaying the fall in intracellular pH and enhancing glycogenolytic ATP production [7,8]. In addition, CIT has been shown to increase plasma volume (PV) [9,10] to an extent that may improve endurance performance through slowing down increases in core body temperature (Tc) during exercise [11]. ...
... Cooper et al. [48] and Rhind et al. [49] reported a significant relationship between exercise-induced increases in Tc and plasma CORT levels. In our participants, CIT ingestion induced acute PV expansion that may slow down increases in Tc during exercise [11]. However, lower serum CORT level in CIT trial occurred already before the start of the TT when Tc did not differ. ...
Full-text available
Background and objectives: In temperate environments, acute orally induced metabolic alkalosis alleviates exercise stress, as reflected in attenuated stress hormone responses to relatively short-duration exercise bouts. However, it is unknown whether the same phenomenon occurs during prolonged exercise in the heat. This study was undertaken with aim to test the hypothesis that ingestion of an alkalizing substance (sodium citrate; CIT) after dehydrating exercise would decrease blood levels of stress hormones during subsequent 40 km cycling time-trial (TT) in the heat. Materials and Methods: Male non-heat-acclimated athletes (n = 20) lost 4% of body mass by exercising in the heat. Then, during a 16 h recovery period prior to TT in a warm environment (32 °C), participants ate the prescribed food and ingested CIT (600 mg·kg−1) or placebo (PLC) in a double-blind, randomized, crossover manner with 7 days between the two trials. Blood aldosterone, cortisol, prolactin and growth hormone concentrations were measured before and after TT. Results: Total work performed during TT was similar in the two trials (p = 0.716). In CIT compared to PLC trial, lower levels of aldosterone occurred before (72%) and after (39%) TT (p ˂ 0.001), and acute response of aldosterone to TT was blunted (29%, p ˂ 0.001). Lower cortisol levels in CIT than in PLC trial occurred before (13%, p = 0.039) and after TT (14%, p = 0.001), but there were no between-trial differences in the acute responses of cortisol, prolactin or growth hormone to TT, or in concentrations of prolactin and growth hormone before or after TT (in all cases p > 0.05). Conclusions: Reduced aldosterone and cortisol levels after TT and blunted acute response of aldosterone to TT indicate that CIT ingestion during recovery after dehydrating exercise may alleviate stress during the next hard endurance cycling bout in the heat.
... Hydration also normalizes blood rheology during exercise, despite the stress caused by heat exposure [110,114]. Moreover, the inclusion of sodium in the rehydration solution restores plasma volume when ingested during exercise, and expands plasma volume if ingested pre-exercise [115]. ...
... Several included studies also did not measure blood bicarbonate levels after sodium bicarbonate ingestion, which is a limitation given that the increase in blood bicarbonate (from baseline to pre-exercise), is one of the key determinants of the ergogenic effects of this supplement (8,9). Even though the goal of sodium bicarbonate is to increase blood bicarbonate levels, it should be taken into account that isolated ingestion of salt may also be ergogenic in some cases (36). However, only three included studies provided a placebo where the sodium content contained an equimolar amount of salt to the sodium bicarbonate dose. ...
The review aimed to perform a meta-analysis of studies exploring the acute effects of sodium bicarbonate on Wingate test performance. Ten databases were searched to find studies that examined the effects of sodium bicarbonate on single and repeated Wingate tests. Meta-analyses were performed using the random-effects model. Ten studies were included in the review. There was no significant difference between the sodium bicarbonate and placebo trials for mean power in Wingate test 1 (standardized mean difference [SMD] = 0.02; 95% confidence interval [CI]: −0.07, 0.11) and test 3 (SMD = 0.21; 95% CI: −0.16, 0.58). There was a significant effect of sodium bicarbonate on mean power in Wingate test 2 (SMD = 0.09; 95% CI: 0.03, 0.16), and test 4 (SMD = 0.62; 95% CI: 0.15, 1.08). When considering studies that used shorter rest intervals between repeated Wingate tests, a significant effect of sodium bicarbonate was found on mean power in Wingate test 3 (SMD = 0.40; 95% CI: 0.01, 0.80). There was no significant difference between the sodium bicarbonate and placebo trials for peak power in Wingate test 1 (SMD = −0.01; 95% CI: −0.06, 0.04), test 2 (SMD = 0.02; 95% CI: −0.10, 0.13), or test 4 (SMD = 0.29; 95% CI: −0.13, 0.71). There was a significant effect of sodium bicarbonate on peak power in test 3 (SMD = 0.09; 95% CI: 0.00, 0.17). The results of this review suggest that sodium bicarbonate may provide an ergogenic effect on measures of repeated Wingate test performance. • Key Teaching Points • Sodium bicarbonate is a popular ergogenic aid. The Wingate test is commonly used to evaluate high-intensity exercise performance. While several studies explored the effects of sodium bicarbonate ingestion on Wingate test performance, the findings are conflicting. • In this meta-analysis, 10 studies that examined the acute effects of sodium bicarbonate on single and/or repeated Wingate test performance were included. • There was no significant difference between sodium bicarbonate and placebo trials for mean or peak power in a single Wingate test. • However, sodium bicarbonate was ergogenic for mean power in repeated Wingate tests. Specifically, an ergogenic effect was found in test 2 and test 4 (standardized mean difference: 0.09 to 0.62). When considering only studies that used shorter rest intervals between repeated Wingate tests, an ergogenic effect was found in test 3 (standardized mean difference: 0.40). • Sodium bicarbonate was also ergogenic for peak power in Wingate test 3, but with small effects (standardized mean difference: 0.09).
... We believe that during the TC digestion process some bioactive peptide with haematopoietic properties can be obtained. In addition, we believe that the high levels of sodium and chloride present in TC could increase fluid retention and generate hypervolaemia, thereby decreasing haematocrit [53,54]. Further research is needed to explain the results obtained. ...
Full-text available
This study aimed to analyse the effects of Tetraselmis chuii (TC) microalgae supplementation during thirty days on ergospirometric, haematological and biochemical parameters in amateur soccer players. Thirty-two amateur soccer players divided into a control group (CG; n = 16; 22.36 ± 1.36 years; 68.36 ± 3.53 kg) and a supplemented group (SG; n = 16; 22.23 ± 2.19 years; 69.30 ± 5.56 kg) participated in the double-blind study. SG ingested 200 mg of the TC per day, while CG ingested 200 mg per day of lactose powder. Supplementation was carried out for thirty days. The participants performed a maximal treadmill test until exhaustion. The ergospirometric values at different ventilatory thresholds and haematological values were obtained after the test. Heart rate decreased after supplementation with TC (p < 0.05). Oxygen pulse, relative and absolute maximum oxygen consumption increased in SG (pre vs. post; 19.04 ± 2.53 vs. 22.08 ± 2.25; 53.56 ± 3.26 vs. 56.74 ± 3.43; 3.72 ± 0.35 vs. 3.99 ± 0.25; p < 0.05). Haemoglobin and mean corpuscular haemoglobin increased in SG (pre vs. post; 15.12 ± 0.87 vs. 16.58 ± 0.74 p < 0.01; 28.03 ± 1.57 vs. 30.82 ± 1.21; p < 0.05). On the other hand, haematocrit and mean platelet volume decreased in SG (p < 0.05). TC supplementation elicited improvements in ergospirometric and haematological values in amateur soccer players. TC supplementation could be valuable for improving performance in amateur athletes.
... 34,48,70 Mora-Rodriguez and Hamouti focused on the importance of pre-exercise plasma volume expansion in endurance performance following the ingestion of saline solutions and showed that acute plasma volume expansion in the range of 7%-8% can improve performance of 20% on average. 69 Suvi et al, for the first time, studied the impact of SC ingestion on cycling performance during 40 km of TT in a warm environment. 70 Similarly to the Timpmann study, 67 participants consumed SC (0.6 g × kg −1 bw) in a 16 hours rest period after losing 4% of their bw through exercise in the heat, and before 40 km TT the plasma volume was 7.8% higher in the SC group compared to 0.9% observed in the placebo group. ...
Full-text available
Based on the assumption that a significant buffering capacity is able to attenuate the negative pH changes associated with high intensity physical exercise, numerous studies have been focused on the effects the exogenous administration of sodium citrate (SC) on human performance. However, the exact mechanisms of action of citrates have never been accurately described and results obtained so far often failed to demonstrate a significant advantage, mainly to an unfavorable relationship between achievable benefits and risk of side effects. In recent years, new evidence has emerged on the fields of use of SC supplementation in sports thus providing the theoretical basis for its use after dehydrating exercise to promote a fast fluid recovery. The aim of this review is to highligths recent experimental observations that could provide new interest in this buffering agent.
... Therefore, future studies in women and/or older adults are warranted. It also needs to be mentioned that there are cases in which isolated sodium ingestion has been reported to be ergogenic for exercise performance [59]. Therefore, to isolate the effects of bicarbonate, some studies use sodium-matched placebos [60]. ...
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Background: The effects of sodium bicarbonate on muscular strength and muscular endurance are commonly acknowledged as unclear due to the contrasting evidence on the topic. Objective: To conduct a systematic review and meta-analysis of studies exploring the acute effects of sodium bicarbonate supplementation on muscular strength and endurance. Methods: A search for studies was performed using five databases. Meta-analyses of standardized mean differences (SMDs) were performed using a random-effects model to determine the effects of sodium bicarbonate supplementation on muscular strength (assessed by changes in peak force [N], peak torque [N.m], or maximum load lifted [kg]) and muscular endurance (assessed by changes in the number of repetitions performed or time to maintain isometric force production). Subgroup meta-analyses were conducted for the muscular endurance of small vs. large muscle groups and muscular strength tested in a rested vs. fatigued state. A random-effects meta-regression analysis was used to explore possible trends in the effects of: (a) timing of sodium bicarbonate ingestion; and (b) acute increase in blood bicarbonate concentration (from baseline to pre-exercise), on muscular endurance and muscular strength. Results: Thirteen studies explored the effects of sodium bicarbonate on muscular endurance and 11 on muscular strength. Sodium bicarbonate supplementation was found to be ergogenic for muscular endurance (SMD = 0.37; 95% confidence interval [CI]: 0.15, 0.59; p = 0.001). The performance-enhancing effects of sodium bicarbonate were significant for both small (SMD = 0.31; 95% CI: 0.04, 0.59; p = 0.025) and large muscle groups (SMD = 0.40; 95% CI: 0.13, 0.66; p = 0.003). Sodium bicarbonate ingestion was not found to enhance muscular strength (SMD = –0.03; 95% CI: –0.18, 0.12; p = 0.725). No significant effects were found regardless of whether the testing was carried out in a rested (SMD = 0.02; 95% CI: –0.09, 0.13; p = 0.694) or fatigued (SMD = –0.16; 95% CI: –0.59, 0.28; p = 0.483) state. No significant linear trends in the effects of timing of sodium bicarbonate ingestion or acute increase in blood bicarbonate concentrations on muscular endurance or muscular strength were found. Conclusions: Overall, sodium bicarbonate supplementation acutely improves muscular endurance of small and large muscle groups, but no significant ergogenic effect on muscular strength was found.
... In this case, the level of blood sugar might be more influential on the performance (Pottier et al., 2010). Due to the low degree of fluid loss, we do not assume changes in the cardiovascular system, as can be observed in the form of increased heart rates during long-term exertion and severe loss of sweat (Mora-Rodriguez & Hamouti, 2012). Even if the placebo group exhibited a higher heart rate, studies show that water and saline solutions can have similar effects on the heart rate when administered during exertion (Mora-Rodriguez & Hamouti, 2012). ...
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Background: Carbohydrate-electrolyte drinks support performance and recovery during athletic activities. The impact of these isotonic drinks is usually verified by means of placebos without energy. Objective: We checked the extent to which commercial sports drinks may be superior to a syrup-water mixture, similar in calorific value, during an intermittent exertion. Method: In a cross-sectional study, three homogeneously parallelized groups, including a total of 35 test subjects, performed full-strain endurance and speed tests (5,000 m, 3,000 m, 1,500 m, 800 m, 400 m, and 200 m). During the rest intervals, isocaloric drinks with the same CHO (6,66-7,0 g), but different sugar (ISO1: 2,46 g; ISO2: 5,6 g; syrup: 6,7 g) and electrolyte content were given in a randomized way. The parameters of running performance, body weight, rating of perceived exertion, heart rate, and blood lactate concentration were analyzed. Results: Over the distances (p≥0.10), the results did not show any ergogenic effect of the isotonic drinks in comparison with the syrup-water mixture. There were also no significant differences in terms of rates of perceived exertion (p≥0.26) and the physiological parameters of heart rate (p≥0.30) and blood lactate (p≥0.18) among the groups. Conclusion: During intermittent and repetitive exertion below 30 minutes, homemade energy drinks exhibited the same effects as commercial sports drinks.
Introduction: The Athlete's Biological Passport (ABP) is a tool for the indirect detection of blood doping. Guidelines from the World Anti-Doping Agency (WADA) require a 2 hours delay after any physical exercise, and to be seated for 10 minutes before collecting an ABP sample. This study investigated posture-related hematological variations with changes in body position during blood sampling. Methods: Ten successive venous blood samples from 38 subjects were collected in three situations: immediately after 10-minutes of normalized activity (B1), after 10-minutes seated (B2, typical reference sample in an anti-doping context), after a 50 m walk (B3), after 5 and 10-minutes in a seated position again (B4 and B5), and finally after 5-30 minutes supine (B6-B10). Hemoglobin concentration [Hb] and hematocrit (Hct) were determined by flow cytometry to assess putative posture-related variations. Results: Reticulocytes percentage was unchanged in all conditions, [Hb] and Hct were stable after at least 10-minutes in a seated position. Due to shifts in plasma volume, [Hb] and Hct increased slightly but significantly higher after changing posture for a short walk (+0.1 gr/dL [P = .008] and +0.4% [P = .01] respectively), but readjusted to previous levels after only 5 minutes. Supine position (>10 minutes) induced decreases of [Hb] (-0.2 g/dL in average, P < .01) and Hct (-1.1%, in average, P < .01). Conclusion: The observed variations in [Hb] and Hct may have minor clinical significance, while they underline the need to follow strict guidelines for posture before and during blood sampling in an anti-doping context.
The health and performance of ultra-endurance athletes is dependent on avoidance of performance limiting hypohydration while also avoiding the potentially fatal consequences of exercise-associated hyponatremia due to overhydration. In this work, key factors related to maintaining proper hydration during ultra-endurance activities are discussed. In general, proper hydration need not be complicated and has been well demonstrated to be achieved by simply drinking to thirst and consuming a typical race diet during ultra-endurance events without need for supplemental sodium. As body mass is lost from oxidation of stored fuel, and water supporting the intravascular volume is generated from endogenous fuel oxidation and released with glycogen oxidation, the commonly promoted hydration guidelines of avoiding body mass losses of >2% can result in overhydration during ultra-endurance activities. Thus, some body mass loss should occur during prolonged exercise, and appropriate hydration can be maintained by drinking to the dictates of thirst.
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Fluid is typically administered via intravenous (IV) infusion to athletes who develop clinical symptoms of heat illness, based on the perception that dehydration is a primary factor contributing to the condition. However, other athletes also voluntarily rehydrate with IV fluid as opposed to, or in conjunction with, oral rehydration. The voluntary use of IV fluids to accelerate rehydration in dehydrated, though otherwise healthy athletes, has recently been banned by the World Anti-Doping Agency. However, the technique remains appealing to many athletes. Given that it now violates the Anti-Doping Code, it is important to determine whether potential benefits of using this technique outweigh the risks involved. Several studies have shown that rehydration is more rapid with IV fluid. However, the benefits are generally transient and only small differences to markers of hydration status are seen when comparing IV and oral rehydration. Furthermore, several studies have shown improvements in cardiovascular function and thermoregulation with IV fluid, while others have indicated that oral fluid is superior. Subsequent exercise performance has not been improved to a greater extent with one technique over the other. The paucity of definitive findings is probably related to the small number of studies investigating these variables and the vast differences in the designs of studies that have been conducted. The major limitation of IV rehydration is that it bypasses oropharyngeal stimulation, which has an influence on factors such as thirst sensation, antidiuretic hormone (arginine vasopressin) release, cutaneous vasodilation and mean arterial pressure. Further research is necessary to determine the relative benefits of oral and IV rehydration for athletes.
Sweat Na(+) concentration ([Na(+)]) varies greatly among individuals and is particularly high in cystic fibrosis (CF). The purpose of this study was to determine whether excess sweat [Na(+)] differentially impacts thirst drive and other physiological responses during progressive dehydration via exercise in the heat. Healthy subjects with high-sweat [Na(+)] (SS) (91.0 ± 17.3 mmol/l), Controls with average sweat [Na(+)] (43.7 ± 9.9 mmol/l), and physically active CF patients with very high sweat [Na(+)] (132.6 ± 6.4 mmol/l) cycled in the heat without drinking until 3% dehydration. Serum osmolality increased less (P < 0.05) in CF (6.1 ± 4.3 mosmol/kgH(2)O) and SS (8.4 ± 3.0 mosmol/kgH(2)O) compared with Control (14.8 ± 3.5 mosmol/kgH(2)O). Relative change in plasma volume was greater (P < 0.05) in CF (-19.3 ± 4.5%) and SS (-18.8 ± 3.1%) compared with Control (-14.3 ± 2.3%). Thirst during exercise and changes in plasma levels of vasopressin, angiotensin II, and aldosterone relative to percent dehydration were not different among groups. However, ad libitum fluid replacement was 40% less, and serum NaCl concentration was lower for CF compared with SS and Control during recovery. Despite large variability in sweat electrolyte loss, thirst appears to be appropriately maintained during exercise in the heat as a linear function of dehydration, with relative contributions from hyperosmotic and hypovolemic stimuli dependent upon the magnitude of salt lost in sweat. CF exhibit lower ad libitum fluid restoration following dehydration, which may reflect physiological cues directed at preservation of salt balance over volume restoration.
To evaluate the influence of acute hypervolemia, achieved through the ingestion of a sodium citrate-rich beverage, on cardiovascular strain and thermoregulatory function, during moderate-intensity aerobic exercise in a warm environment. Sodium citrate's ability to increase buffering capacity was also assessed. Twelve endurance-trained athletes completed two blind randomized treatment trials, separated by a minimum of seven days, on a cycle ergometer under heat stress (30.9 degrees C, 64% RH). The subjects ingested 12 of (1) Gatorade, the control (CNT), or (2) sodium-citrate plus Gatorade (NaCIT: 170 mmol Na+L(-1)) before cycling at 15% below ventilatory threshold (VT) for 62 minutes. Core and skin temperature, expired gas samples, heart rate, and perceived exertion were measured throughout exercise. Blood samples were taken before drinking each beverage, before commencing exercise, and throughout the exercise bout. Plasma volume (PV) was significantly expanded in the NaCIT trial (3.6+/-5.5%) and remained significantly higher throughout exercise in the NaCIT trial compared with the CNT trial (P<or=.05). No significant differences were found in heart rate, in core and skin temperature, or in the metabolic data between the treatment groups. NaCIT significantly increased [HCO3-], base excess, and pH throughout the trial. Acute oral ingestion of high-sodium citrate beverages before moderate exercise induces mild levels of hypervolemia and improves blood-buffering capacity in humans; however, mild hypervolemia during 62 minutes of moderate exercise does not reduce physiological strain or improve thermoregulation.
The effect of alterations in intravascular volume and tonicity on thermoregulatory and cardiovascular responses to heat and exercise have been compared in four subjects. Core temperatures were found to be significantly higher during dehydration, and when dehydration was prevented by administration of 1% saline, than when dehydration was prevented by water administration. These higher temperatures were associated with elevated levels of plasma [Na] and osmolarity, but no consistent relationship between temperature and changes in intravascular volume could be demonstrated. Relationships observed between core temperature and plasma tonicity were consistent with the hypothesis that the adverse effects of dehydration on thermoregulation can be attributed to an inhibition of sweating mediated by an increase in either plasma osmotic pressure or plasma [Na]. In separate experiments the heart rate response to exercise was shown to be reduced by saline, compared with water and dehydration, and this may be explained by the smaller reduction in intravascular volume which occurs during exercise following administration of hypertonic saline. It is concluded that the effects of reduced intravascular volume, and increased intravascular tonicity on physical work capacity may be distinguished by the adverse effect on the cardiovascular system of the former, and on the thermoregulatory system of the latter.
Controversy exists as to whether plasma volume (PV) expansion has the potential to increase maximal oxygen uptake (VO2max). In the present study, VO2max and exercise time to fatigue were measured in nine untrained men when plasma volume (PV) was normal and then again on the next day following two levels of PV expansion. Resting PV was expanded (via intravenous infusion of a 6% dextran solution) by 282 +/- 16 ml (i.e., PVX-1) and then by 624 +/- 26 ml (i.e., PVX-2). PVX-1 increased stroke volume (CO2 rebreathing) during submaximal exercise by 15% (P less than 0.05) above normal levels. VO2max following PVX-1 was increased 4% (P less than 0.05; 3.78 to 3.92 l/min) despite a 4% reduction in hemoglobin concentration. Exercise time to fatigue was also increased (P less than 0.05). PVX-2 resulted in an 11% (P less than 0.05) reduction in hemoglobin concentration during maximal exercise and a return of VO2max and exercise time to normal levels. In summary, we have observed in untrained men that 200-300 ml of PV expansion increases SV, measured during submaximal exercise, yet causes only a small amount of hemodilution. As a result, VO2max is increased slightly and performance is improved. Further PV expansion to levels 500-600 ml above normal results in an excessive hemodilution and a subsequent decline in VO2max and performance to normal levels. There is an optimal PV for eliciting VO2max in untrained men which appears to be approximately 200-300 ml above their normal levels.
To clarify the role of progressive heavy training on vascular volumes and hematologic status, seven untrained males [maximal O2 uptake (VO2max) = 45.1 +/- 1.1 (SE)] cycled 2 h/day at an estimated 62% of VO2max. Training was conducted five to six times per week for approximately 8 wk. During this time, VO2max increased (P less than 0.05) by 17.2%. Plasma volume (PV) measured by 125I increased (P less than 0.05) from 3,068 +/- 104 ml at 0 wk to 3,490 +/- 126 ml at 4 wk and then plateaued during the remaining four wk (3,362 +/- 113 ml). Red cell (RBC) mass (RCM) measured by 51Cr-labeled RBC did not change during the initial 4 wk of training (2,247 +/- 66 vs. 2,309 +/- 128 ml). As well, no apparent change occurred in RCM during the final 4 wk of training when RCM was estimated using PV and hematocrit (Hct). Collectively, PV plus RCM, expressed as total blood volume (TBV), increased (P less than 0.05) by 10% at 4 wk and then stabilized for the final 4 wk. During the initial phase of training, reductions (P less than 0.05) were also noted in Hct (4.6%), hemoglobin (Hb, 4.0%), and RBC count (6.3%). In contrast, an increase in mean cell volume (MCV, 1.7%) and mean cell Hb (2.3%) was observed (P less than 0.05). From 4 to 8 wk, no further changes (P greater than 0.05) in Hb, RBC, and MCV were found, whereas both mean cell Hb and Hct returned to pretraining levels.(ABSTRACT TRUNCATED AT 250 WORDS)
To quantify the effect of an acute increase in plasma volume (PV) on forearm blood flow (FBF), heart rate (HR), and esophageal temperature (Tes) during exercise, we studied six male volunteers who exercised on a cycle ergometer at 60% of maximal aerobic power for 50 min in a warm [(W), 30 degrees C, less than 30% relative humidity (rh)] or cool environment [(C), 22 degrees C, less than 30% rh] with isotonic saline infusion [Inf(+)] or without infusion [Inf(-)]. The infusion was performed at a constant rate of 0.29 body wt-1.min-1 for 20-50 min of exercise to mimic fluid intake during exercise. PV decreased by approximately 5 ml/kg body wt within the first 10 min of exercise in all protocols. Therefore, PV in Inf(-) was maintained at the same reduced level by 50 min of exercise in both ambient temperatures, whereas PV in Inf(+) increased toward the preexercise level and recovered approximately 4.5 ml/kg body wt by 50 min in both temperatures. The restoration of PV during exercise suppressed the HR increase by 6 beats/min at 50 min of exercise in W; however, infusion had no effect on HR in C. In W, FBF in Inf(+) continued to increase linearly as Tes rose to 38.1 degrees C by the end of exercise, whereas FBF in Inf(-) plateaued when Tes reached approximately 37.7 degrees C. The infusion in C had only a minor effect on FBF.(ABSTRACT TRUNCATED AT 250 WORDS)
We tested the hypothesis that volume infusion during strenuous exercise, by expanding blood volume, would allow better skin blood flow and better temperature homeostasis and thereby improve endurance time. Nine males exercised to exhaustion at 84.0 +/- 3.14% (SE) of maximum O2 consumption on a cycle ergometer in a double-blind randomized protocol with either no infusion (control) or an infusion of 0.9% NaCl (mean vol 1,280.3 +/- 107.3 ml). Blood samples and expired gases (breath-by-breath), as well as core and skin temperatures, were analyzed. Plasma volume decreased less during exercise with the infusion at 15 min (-13.7 +/- 1.4% control vs. -5.3 +/- 1.7% infusion, P less than 0.05) and at exhaustion (-13.6 +/- 1.2% vs. -1.3 +/- 2.2%, P less than 0.01). The improved fluid homeostasis was associated with a lower core temperature during exercise (39.0 +/- 0.2 degrees C for control and 38.5 +/- 0.2 degrees C for infusion at exhaustion, P less than 0.01) and lower heart rate (194.1 +/- 3.9 beats/min for control and 186.0 +/- 5.1 beats/min for infusion at exhaustion, P less than 0.05). However, endurance time did not differ between control and infusion (21.96 +/- 3.56 and 20.82 +/- 2.63 min, respectively), and neither did [H+], peak O2 uptake, and CO2 production, end-tidal partial pressure of CO2, blood lactate, or blood pressure. In conclusion, saline infusion increases heat dissipation and lowers core temperature during strenuous exercise but does not influence endurance time.
We investigated the effects of a decrease in plasma volume (PV) and an increase in plasma osmolality during exercise on circulatory and thermoregulatory responses. Six subjects cycled at approximately 65% of their maximum O2 uptake in a warm environment (30 degrees C, 40% relative humidity). After 30 min of control (C) exercise (no infusion), PV decreased 13.0%, or 419 +/- 106 (SD) ml, heart rate (HR) increased to 167 +/- 3 beats/min, and esophageal temperature (Tes) rose to 38.19 +/- 0.09 degrees C (SE). During infusion studies (INF), infusates were started after 10 min of exercise. The infusates contained 5% albumin suspended in 0.45, 0.9, or 3.0% saline. The volume of each infusate was adjusted so that during the last 10 min of exercise PV was maintained at the preexercise level and osmolality was allowed to differ. HR was significantly lower (10-16 beats/min) during INF than during C. Tes was reduced significantly during INF, with trends for increased skin blood flow and decreased sweating rates. No significant differences in HR, Tes, or sweating rate occurred between the three infusion conditions. We conclude that the decrease in PV, which normally accompanies moderate cycle exercise, compromises circulatory and thermal regulations. Increases in osmolality appear to have small if any effects during such short-term exercise.