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211
Nutritional Supplement for Athletic Performance: Based on
Australian Institute of Sport Sports Supplement Framework
Jooyoung Kim
Department of Anatomy, School of Medicine, Kyungpook National University, Daegu, Korea
Introduction nutrition is essential for athletic performance, condition-
ing, and recovery from fatigue after exercise [1]. In this context, the use
of nutritional supplements (also called ergogenic aids) is a matter of great
interest for athletes. Although many nutritional supplements are used,
there is debate about whether they actually have effects on athletes’ per-
formance, and several nutritional supplements are not sufficiently sup-
ported by scientific evidence [2]. Indeed, the use of some nutritional sup-
plements is being stopped due to side effects or positive doping tests [3].
In order to reduce these issues, the Australian Institute of Sport (AIS)
developed the Sports Supplement Framework. This classifies nutritional
supplements into 4 groups (A, B, C, and D) based on scientific evidence,
safety, legality, and effectiveness in improving sports performance. The
nutritional supplements in Group A of the AIS Sports Supplement
Framework possess strong scientific evidence and are permitted for ath-
letes according to best practice protocols. This group includes sports
food (sports drink, sports gel, sports bar, isolated protein supplement,
etc.), medical supplements (iron, calcium, multivitamin, etc.), and perfor-
mance supplements (caffeine, beta-alanine, bicarbonate, beetroot juice,
creatine, and glycerol) [4].
The performance supplements in Group A are supported by sports
nutrition expert groups and the latest literature [5-7]. In the International
Society of Sports Nutrition (ISSN) exercise & sports nutrition review,
Kerksick et al. [6] report that there is strong evidence for the efficacy and
safety of beta-alanine, caffeine, creatine, and bicarbonate, and in a con-
sensus statement by the International Olympic Committee (IOC),
Maughan et al. [7] included creatine, nitrate, bicarbonate, and beta-ala-
nine as performance-enhancing supplements with an adequate level of
support to indicate the potential for performance enhancement. Close et
al. [5] classified performance supplements with strong evidence into
those for endurance (caffeine, beta-alanine, beetroot juice, bicarbonate)
and those for strength/size (creatine). In summary, in order for athletes
to safely and effectively utilize performance supplements in competition
and training, it is important to investigate the level of scientific evidence.
Group B of the AIS Sports Supplement Framework includes food
REVIEW
ARTICLE
Corresponding author: Jooyoung Kim Tel +82-53-420-4910 Fax +82-53-422-9195 E-mail hirase1125@hanmail.net
Received 2 Jun 2019 Revised 22 Jul 2019 Accepted 29 Jul 2019
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use,
distribution, and reproduction in any medium, provided the original work is properly cited.
ISSN(Online) 2384-0544
INTRODUCTION: Many athletes use nutritional supplements for their performance enhancements and training effects. However, it is
unclear that some of the dietary supplements have favorable outcomes, and others may increase the risk of doping or side effects.
METHODS: In this review, we discuss the Australian Institute of Sport (AIS) Sports Supplement Framework’s Group A performance
supplements regarding safety, legality, and effectiveness in improving sports performance. Group A supplements include caffeine, beta-
alanine, bicarbonate, beetroot juice, creatine, and glycerol.
RESULTS: We found the use of these performance supplements could help athletes improve strength and endurance. However, the
effects vary with individual athletes and depend on sports characteristics, training content, physical condition, and habits.
CONCLUSIONS: Therefore, a case-by-case approach is warranted to ensure their desirable effects. It is important to consult a doctor or
sports nutritionist before consuming theses supplements and to monitor the individual’s response through simulation.
Key words: Beetroot juice, Beta-alanine, Bicarbonate, Caffeine, Creatine, Glycerol
Exercise Science
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polyphenols (cherries, berried, quercitin, epigallocatechin gallate, etc.),
other (collagen support, carnitine, β-Hydroxy β-methylbutyric acid, fish
oils, etc.), sick pack (zinc lozenges and vitamin C), and amino acids
(branched-chain amino acids and leucine). Group C contains all other
nutritional supplements that are not found in Groups A or B. Finally,
Group D contains substances banned by the World Anti-Doping Agen-
cy (WADA), such as stimulants (ephedrine, strychnine, sibutramine, etc.)
and prohormones and hormone boosters (dehydroepiandrosterone, an-
drostenedione, 19-norandrostenione/ol, etc.) [4].
The purpose of our study is to enable coaches, trainers, and athletes to
safely and effectively utilize caffeine, beta-alanine, bicarbonate, beetroot
juice, creatine, and glycerol, which are included in the Group A perfor-
mance supplements in the AIS Sports Supplement Framework, by pro-
viding information about their effectiveness and recommendations.
PERFORMANCE SUPPLEMENTS
1. Caffeine
Caffeine (1, 3, 7-trimethylxanthine) is a major component of tea, cof-
fee, guarana, and cacao [8]; it is a pharmacologic and psychoactive sub-
stance that is consumed frequently worldwide [9]. In sports, caffeine is a
well known nutritional supplement, and has been actively studied since
the 1970s [10].
Generally, caffeine helps to improve endurance, strength, and power
Table 1. Recommendations for performance supplements
Performance
Supplements Recommendations
Caffeine - The dose of caffeine should be in the range 3-6 mg/kg b.w. High doses, such as 9 mg/kg b.w. may be ineffective [16,17] .
- Caffeine can be consumed as coffee, in an anhydrous state (capsule/tablet, powder), or as chewing gum [17,24,25].
- A single can of caffeine-containing energy drink does not provide the required caffeine dose [22,23].
- Good timing for caffeine intake is 60 minutes before competition or training [17].
- Potential side effect: headaches, gastrointestinal upset, nervousness, mental confusion, and disturbed sleeping [10].
Beta-alanine - To improve athletic performance, beta-alanine should be taken for at least 2-4 weeks [26].
- Beta-alanine can generally be consumed within a range of 4-6 g/day [26].
- If symptoms such as paresthesia develop after taking beta-alanine, intake can be split across several doses per day (e.g., 1.6 g doses) [26].
- Beta-alanine can be taken after a meal at breakfast, lunch, and dinner [35,36].
Bicarbonate - In bicarbonate supplementation, it is effective to use a loading protocol to increase serum bicarbonate concentration and buffering ca-
pacity [45,46].
- L oading protocols Acute loading: 0.3 g/kg b.w., taken 1-3 hours before competition or training [45].
S erial loading: 0.3-0.5 g/kg b.w. (divided into 3-4 doses/day), taken for 3-5 days before competition
or training [46].
- D uring bicarbonate supplementation, side effects, such as gastrointestinal distress, can be reduced by methods such as multiday in-
gestion, chronic progressive-dose, or split-dose protocols [47,48].
Beetroot juice - Beetroot juice can be consumed 90 minutes before competition or training [50].
- Beetroot juice can be consumed at a dose of 500 mL/day (around 2 cups) (the beetroot juice should contain 5-8.4 mmol nitrate) [55,58].
- Both acute (single dose) and chronic (doses for 6-7 days) beetroot juice intake are effective at improving exercise performance [60,61].
- If beetroot juice is consumed, oral antiseptic rinses should be avoided [50].
- No side effects have been reported.
Creatine -
C reatine loading is generally proposed to increase intramuscular creatine capacity. Creatine loading consists of a loading phase (0.3 g/kg
b.w. or 20-30 g/day, divided into 3-4 doses/day, for 3-5 days) and a maintain phase (3-5 g/day after the loading phase) [72].
- A small amount of creatine (3-5 g/day) can be taken from the start, without creatine loading [63].
- During creatine intake, it is still not clear whether a washout phase is required. More scientific evidence is required in this area [74,75].
- Creatine can be taken in a mixture together with carbohydrates or carbohydrates and proteins [76].
- In terms of timing for creatine intake, post-exercise intake is more effective than pre-exercise intake [78,79].
- Potential side effect: dehydration, muscle cramping, and gastrointestinal upset [63].
Glycerol - G lycerol intake can help to prevent dehydration and improve endurance performance during competition or training in high-tempera-
ture environments [89-91].
- Glycerol can be take before or during exercise. Refer to the protocols below [87,92,93].
- Protocols for glycerol intake P re-exercise: It is recommended to take 1.2 g/kg b.w. of glycerol with 26 mL/kg b.w. of fluid during
60 minutes [86].
D uring exercise: If glycerol was taken pre-exercise, 0.125 g/kg b.w. of glycerol should be taken with
5 mL/kg b.w. of fluid; if glycerol was not taken pre-exercise, 0.4 g/kg b.w. of glycerol should be
taken with fluid during each of the first 4 hours of exercise [85].
- Glycerol can be taken with an electrolyte sports drink [88].
- Potential side effect: nausea, gastrointestinal discomfort, dizziness, and headaches [85].
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Juyoung Kim • Nutritional Supplement and Athletic Performance| 213
by activating various biologic mechanisms [11]. Caffeine stimulates the
sympathetic nervous system and increases the blood epinephrine con-
centration, promoting lipolysis of adipose and intramuscular triglycer-
ides. These changes conserve stored glycogen and improve endurance
performance. This is referred to as the glycogen sparing effect [8]. Potgi-
eter et al. [11] reported that 6 mg/kg body weight (b.w.) of caffeine intake
before exercise reduced swim time and time to completion by 3.7% and
1.3%, respectively, in triathletes. Felippe et al. [12] reported that 5 mg/kg
b.w. of caffeine intake before exercise resulted in faster 4-km cycling time
trials in cyclists.
Caffeine is able to help improve strength and power because it in-
creases the intracellular Ca2+ concentration by stimulating the sarcoplas-
mic reticulum in muscle fibers, while also affecting excitation-contrac-
tion coupling by inhibiting uptake [13]. In fact, Diaz-Lara et al. [14] re-
ported that Jiu-jitsu athletes who took caffeine before exercise showed
improved hand grip force, countermovement jump height, one-repeti-
tion maximum, and mean power during the bench-press exercise, and
Glaister et al. [15] reported that pre-exercise caffeine intake significantly
improves peak anaerobic power output in well-trained men.
In terms of practical applications for athletic performance, factors
such as dose, form, and timing can be considered (Table 1). A caffeine
dose of 3-6 mg/kg b.w. is recommended [16,17]. Recently Chia et al. [18]
reported that intake of 3-6 mg/kg b.w. of caffeine appears to be a safe er-
gogenic aid for ball game athletes. However, doses of caffeine over 9 mg/
kg b.w. show no beneficial effects, and can actually decrease performance
level [19]. It has been reported that caffeine produces a stronger effect
when consumed in an anhydrous state (capsule/tablet, powder) com-
pared to coffee [17], but if the dose is sufficient, pre-exercise caffeine in-
take is effective at improving endurance performance in either state
[20,21]. Several studies have reported that caffeine-containing energy
drinks help to improve athletes’ performance [22,23]. Although some
athletes have tried consuming caffeine in energy drinks, it is important
to be aware that one can does not provide the recommended caffeine in-
take for athletes. For example, the caffeine content in a single can (250
mL) of the well-known energy drink ‘Red Bull’ is only 80 mg. In actual
research, athletes consumed 3 mg/kg b.w. of caffeine from energy drinks,
not just a single can [22,23]. In order to satisfy the caffeine intake sug-
gested in these studies, the athlete needs to drink several cans, and this
requires caution as it could promote weight gain due to unnecessary cal-
orie and carbohydrate intake.
In recent studies, caffeine chewing gum (300 mg of caffeine) was also
reported to help improve muscle function, such as vertical jump height
and knee extension peak torque [24], as well as exercise tolerance [25].
Meanwhile, with regard to the timing of intake, most studies suggested a
protocol for caffeine intake 60 minutes before exercise for optimum ab-
sorption [17]. In addition, caffeine is quickly absorbed into the body after
ingestion. The peak of the blood concentration is shown to be around 30
to 60 minutes after ingestion [19].
2. Beta-alanine
Beta-alanine is a non-essential and non-proteinogenic amino acid
synthesized by the liver, and can also be obtained from foods such as
pork, chicken, or red meat [26]. The main aim of beta-alanine supple-
mentation is to increase intramuscular carnosine (b-alanyl-L-histidine).
Carnosine is a cytoplasmic dipeptide formed when carnosine synthetase
catalyzed the formation of peptide bond between beta-alanine and L-
histidine; carnosine is found in many tissues in the body, but mostly is
present in skeletal muscle [27]. In normal conditions, beta-alanine pro-
duction is relatively low and serum beta-alanine is undetectable, but
when serum beta-alanine increases to detectable levels, intramuscular
carnosine levels are known to also increase [28]. Carnosine synthesis is
controlled by the rate and amount of beta-alanine absorption into mus-
cle fibers, insufficient serum carnosine synthetase activity, beta-alanine
content in food, and hepatic synthesis of amino acids and their transport
to skeletal muscles [29,30]. When beta-alanine is supplemented, 1) beta-
alanine moves into the blood stream via the gastrointestinal tract, 2) be-
ta-alanine and histidine are transported into the muscle sarcoplasm by
amino acid transporters, 3) beta-alanine and histidine are bonded to-
gether in the muscle sarcoplasm by carnosine synthetase to produce car-
nosine [31].
Increased carnosine can improve performance during exercise by buff-
ering hydrogen ion (H
+
) accumulation, limiting the effects of metabolic
acidosis such as reduced phosphofructokinase activity, phosphocreatine
resynthesis and glycolysis inhibition, and competitive inhibition of Ca
2+
at troponin C and delayed Ca
2+
reuptake to the sarcoplasmic reticulum
[32]. Thus, it has also been suggested that the improvements in muscle
strength, power, and endurance following beta-alanine supplementation
are due to increased muscle fiber sensitivity to Ca
2+
and the resulting en-
hancement in excitation-contraction coupling [26]. In practice, Baguet et
al. [33] observed increased carnosine concentration in the soleus and gas-
trocnemius after elite rowers consumed 5 g/day of beta-alanine for 7
weeks, and reported that these changes were positively correlated with
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rowing performance. Saunders et al. [34] also had soccer players consume
3.2 g/day of beta-alanine for 12 weeks, and reported significant improve-
ments in Yo-Yo Intermittent Recovery test (Yo-Yo IR) times.
In order to significantly increase intramuscular carnosine levels, 4-6
g/day of beta-alanine should be consumed for at least 2-4 weeks, and 4-6
g/day of beta-alanine intake is safe for healthy individuals [26] (Table 1).
The optimal timing for beta-alanine intake is not yet well known. With
reference to previous studies, beta-alanine has been taken after each
meal (morning, lunch, and dinner) [35,36]. Adverse events have not
commonly been reported after beta-alanine supplementation, but pares-
thesia can occur [37]. However, when beta-alanine intake is divided
across several small doses (1.6 g/dose) rather than one large dose, pares-
thesia can be reduced [26].
3. Bicarbonate
Bicarbonate (HCO3−) is an extracellular anion that plays an important
role in maintaining extracellular and intracellular pH [38]. In humans at
rest, the blood is slightly alkaline (pH ~7.4) while the muscles are neutral
(pH ~7.0), and this acid-base balance in the blood and muscle is impor-
tant for normal cell metabolism [39]. However, during high-intensity ex-
ercise, acidification of cells occurs. This change interferes with muscle
contraction through negative effects on myosin ATPase, Ca2+ ATPase,
and Na+-K+ ATPase activity, weakens K+ efflux through pH-sensitive po-
tassium channels, and impairs the activity of metabolic enzymes [40]. It
also decreases energy production by lowering the proton gradient be-
tween the mitochondrial matrix and the cell cytoplasm [41].
When bicarbonate is supplemented, bicarbonate loading prevents the
accumulation of H+, which is over-produced by the anaerobic energy
metabolism used in short-duration, high-intensity exercise, which delays
fatigue and allows energy production to continue, ultimately contribut-
ing to improved exercise performance [42]. In other words, bicarbonate
has a similar mechanism and effect to those of beta-alanine, discussed
above. Krustrup et al. [40] analyzed the serum pH after giving trained
young men bicarbonate supplement, and observed higher serum pH
than a control group, accompanied by significantly improved high-in-
tensity intermittent exercise performance. Likewise, Wu et al. [43] re-
ported that bicarbonate supplementation in tennis players resulted in
higher blood pH, and helped to maintain service and forehand ground
stroke consistency scores. Lopes-Silva et al. [44] reported that, when bi-
carbonate supplementation was provided to taekwondo athletes, glyco-
lytic energy contribution increased in the first round of simulated tae-
kwondo combat, resulting in improved exercise performance.
Bicarbonate supplementation needs to occur at the appropriate time
before exercise, and a loading protocol should be utilized, as this can in-
crease the serum bicarbonate concentration and the buffering capacity.
Bicarbonate supplementation can use acute loading or serial loading
methods (Table 1). For acute loading, Price & Singh [45] reported that
bicarbonate needs to be taken 1-3 hours before exercise in order to sig-
nificantly increase serum bicarbonate levels, and Lopes-Silva et al. [44]
reported that 0.3 g/kg b.w. should typically be taken before exercise. Seri-
al loading, which is the method of taking bicarbonate several times per
day for several days, involves 3-4 doses/day of 0.3-0.5 g/kg b.w. for 3-5
days before competition or training [46].
The main reported side effect of bicarbonate is gastrointestinal dis-
tress including nausea, stomach pain, diarrhea and vomiting [42]. In or-
der to reduce these side-effects, methods such as multiday ingestion,
chronic progressive-dose, and split-dose protocols have been suggested
[47,48]. For example, recently, Durkalec-Michalski et al. [47] provided
progressive supplementation of bicarbonate to wrestlers for 10 days, start-
ing from a dose of 25 mg/kg b.w. up to a dose of 100 mg/kg b.w., and re-
ported that this was effective at eliminating side effects, including gastro-
intestinal symptoms.
4. Beetroot juice
Beetroot (Beta vulgaris) juice is a natural food and nutritional supple-
ment that has recently been receiving much attention from athletes and
sports scientists in the field of sports nutrition. Beetroot is known to be
abundant in antioxidants and micronutrients such as potassium, beta-
ine, sodium, magnesium, and vitamin C [49]. Most importantly, beet-
root is a source of nitrate [50]. Nitrate is a naturally existing inorganic
polyatomic anion [49]. When nitrate enters the mouth, it is actively ex-
tracted and concentrated from the saliva and reduced to nitrite by bacte-
ria; in the stomach, nitrite is further reduced, and eventually converted
into nitric oxide (NO) in the muscle [51]. Therefore, nitrate that is sup-
plemented through beetroot juice can be considered a precursor of NO,
and NO contributes to various physiological functions, including vaso-
dilation, mitochondrial respiration, biogenesis, muscle glucose uptake,
angiogenesis, and sarcoplasmic reticulum calcium handling [52]. Fur-
thermore, NO can improve exercise tolerance while reducing muscle
metabolic perturbation (reduction of phosphocreatine and accumulation
of adenosine diphosphate and Pi) that occurs during high-intensity exer-
cise [53].
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Several studies have reported that beetroot juice produces significant
changes in athletic performance [54-57]. Lansley et al. [55] reported that
beetroot juice intake significantly improved power output and 16.1-km
cycling time trials in competitive male cyclists, and Cuenca et al. [54] re-
ported that beetroot juice intake significant improved 30-second cycling
sprint performance in resistance-trained men. Thompson et al. [56] re-
ported that nitrate supplementation by beetroot juice improved sprint
split times and also Yo-Yo IR performance in team-sport players. Wylie et
al. [57] reported that nitrate-rich beetroot juice intake helped recreational
team-sport players to better maintain muscle glucose uptake and muscle
excitability while improving Yo-Yo IR performance. In summary, beet-
root juice intake has been found to be effective at improving power exer-
cise, high-intensity intermittent exercise, and endurance performance.
In order for athletes to benefit from the effects of beetroot juice, sever-
al protocols need to be considered from previous study (Table 1). First,
the appropriate time for beetroot juice intake is approximately 90 min-
utes before competition. The peak nitrate concentration occurs 2-3
hours after beetroot juice intake [50]. It is recommended to consume
500 mL/day (approximately 2 cups) of beetroot juice containing 5-8.4
mmol nitrate [55,58]. According to previous studies, a single dose of
beetroot juice produces an acute effect [55,59], and consuming beetroot
juice for 6-7 days also has a positive effect on exercise performance
[60,61]. Finally, when consuming beetroot juice, oral antiseptic rinses
should be avoided. This is because oral antiseptic rinses inhibit the con-
version of nitrate from beetroot juice to nitrite in the mouth [50].
5. Creatine
Creatine is an amino acid that is synthesized in the liver, kidney, and
pancreas, can be found in high levels in the musculoskeletal system, and
can also be obtained naturally by consuming fish or meat [62]. Creatine
is currently the most effective ergogenic nutritional supplement that can
be used to increase high-intensity exercise ability and lean mass [63]. In
many studies, creatine supplementation has been reported to increase
intramuscular phosphocreatine concentration and high-energy phos-
phate metabolism, helping to improve exercise performance, including
muscle strength [64-66]. In addition, creatine increases calcium re-up-
take into the sarcoplasmic reticulum, enabling rapid detachment of ac-
tin-myosin cross-bridges and augmenting the latent force-generating ca-
pacity [67]. Creatine also increases water retention by cells [68]. Increased
cell size due to creatine-induced water retention is associated with up-
regulation of signaling pathways that mediate protein synthesis, as well
as mechanistic target of rapamycin (mTOR)-mediated signaling [69,70].
These changes help muscle hypertrophy by both stimulating muscle
protein synthesis and reducing breakdown [71].
Creatine is typically taken in a loading phase (0.3 g/kg b.w. or 20-30 g/
day, divided into 3-4 doses/day, for 3-5 days) and a maintain phase (3-5
g/day after the loading phase) [72] (Table 1). This method is called ‘cre-
atine loading’
, and is the optimal method to increase the intramuscular
creatine capacity [73]. Creatine can be taken in small amounts (3-5 g/
day) from the start, without a loading phase, but the initial enhancement
of exercise performance is better if a loading phase is included [63]. In
some studies, long-term intake for at least 3 months could cause down-
regulation of creatine transporter [74,75], and so it has been suggested
that a washout phase is necessary. However, there is still a shortage of
clear evidence for this hypothesis, and further research is required.
Alongside creatine loading, it is recommended that creatine should be
taken in a mixture with carbohydrates or carbohydrates and proteins
[76], since this can promote insulin stimulation [77].
In terms of the timing of creatine intake, post-exercise is recommend-
ed more than pre-exercise [78,79]. Antonio & Ciccone [78] reported that
when creatine was given before or after resistance exercise, post-exercise
supplementation had greater positive effects on body composition and
strength; Candow et al. [79] also reported that creatine supplementation
after resistance exercise resulted in greater augmentation of muscle ac-
cretion and lean tissue mass. One possible reason why post-exercise cre-
atine intake could be more effective is because creatine transport and
accumulation is increased due to higher muscle blood glow and Na+-K+
pump function [80,81].
On the other hand, creatine is not a suitable nutritional supplement
for athletes trying to improve aerobic performance [82]. This is because
aerobic metabolism is affected by triglycerides rather than PCR [83].
6. Glycerol
Glycerol (1, 2, 3-propanetriol) is produced from glucose, protein, py-
ruvate, triacylglycerols and other glycerolipid metabolic pathways [84].
The function of glycerol is to maintain hydration status by increasing
water compartments in the body. The aim of glycerol supplementation is
to create a state of hyperhydration pre-exercise, delays fluid loss and de-
hydration during exercise, and improve the rate of rehydration and total
fluid retention post-exercise [85]. Although maintaining hydration status
pre-exercise is important to improve athletic performance, it is difficult
to drink a large volume of water at once, and this can cause side effects
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such as frequent diuresis [86]. Glycerol can be supplemented to reduce
these issues. Compared to water intake only, glycerol supplementation
increased f luid retention by 400-1,000 mL [87]. For this reason glycerol
is currently sold as a sports supplement for water or sports drink con-
sumption [88].
Glycerol supplementation can be especially effective when exercising
in high-temperature environments [89-91]. According to a study by van
Rosendal et al. [90], when endurance-trained men received intravenous
fluids and glycerol supplementation, plasma volume restoration in-
creased. Wingo et al. [91], administered a water and glycerol mixture to
male mountain bikers, and observed less dehydration compared in a
high-temperature environment compared to water alone, lower pre-ex-
ercise urine volume, and lower post-exercise environmental symptoms
questionnaire scores. Lyons et al. [89] also administered a mixture of
water and glycerol, and reported increased sweat rate and decreased rec-
tal temperature during exercise, resulting in reduced thermal burden in
a high-temperature environment. This changes are ultimately linked to
improvements in exercise performance, especially endurance perfor-
mance. van Rosendal et al. [85] reported that glycerol supplementation
increased endurance time to exhaustion up to 25%. During exercise after
glycerol supplementation, fluid retention helps to reduce dehydration
and cardiovascular strain while improving endurance performance. Ac-
cording to a study by Montner et al. [92], pre-exercise glycerol-enhanced
hyperhydration reduced heart rate and increased endurance time.
Generally, glycerol is used before and during exercise [87,92,93] (Table
1). Pre-exercise, it is recommended to take 1.2 g/kg b.w. of glycerol to-
gether with 26 mL/kg b.w. of fluid in 60 minutes [86]. During exercise,
the glycerol supplementation method is as follows: if glycerol was taken
pre-exercise, 0.125 g/kg b.w. of glycerol should be taken with 5 mL/kg
b.w. of f luid; if glycerol was not take pre-exercise, athletes should take 0.4
g/kg b.w. of glycerol with fluid during each of the first 4 hours of exercise
[85]. Although rare, side-effects during glycerol supplementation can in-
clude nausea, gastrointestinal discomfort, dizziness, and headaches [94].
If an athlete develops these symptoms, they should stop taking glycerol
or reduce the dose [85].
CONCLUSION
In sports, even a small improvement in performance can make a very
important difference. Athletes choose and consume performance sup-
plements for these small differences. In this study, we reviewed caffeine,
beta-alanine, bicarbonate, beetroot juice, creatine, and glycerol, which
are included in Group A performance supplements in the AIS Sports
Supplement Framework. Our review of the literature showed that appro-
priate use of these performance supplements can help to improve ath-
letes’ strength or endurance. However, it is essential for athletes, coaches,
and trainers to understand that the effects of performance supplements
show considerable inter-subject variability, and since there may be differ-
ences in the sport characteristics, training content, physical condition,
and habits, a case-by-case approach is required. Thus, it is important to
assess the risk-benefit ratio of performance supplements, and before use,
a specialist (doctor or sports nutritionist) should be consulted, and the
individual’
s response should be monitored through simulation in a sim-
ilar environment to competition or training.
Before using performance supplements, athletes should ask themselves
several questions. An IOC consensus statement published in 2018 pro-
vided a flow chart to guide informed decision-making regarding ergo-
genic supplement use and reduce the risk of antidoping rule violations.
This flow chart contains a sequence of questions such as ‘Is the athlete
ready for supplement use?’, ‘Should I use this supplement?’, ‘Is supple-
ment effective in my event?’, ‘Is it safe for me to use?’, ‘Supplement
comes from a reliable source?’, and ‘Consistent positive results?’; after
going through these questions, if the response is ‘No/Not known’, the
supplement should not be used [7]. Athletes should always be cautious
about indiscriminate use of performance supplements, and be aware of
the potential risks.
CONFLICT OF INTEREST
No potential conf lict of interest relevant to this article was reported.
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