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Nutritional Supplement for Athletic Performance: Based on Australian Institute of Sport Sports Supplement Framework



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.
Copyright © 2019 Korean Society of Exercise Physiology 
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
Corresponding author: Jooyoung Kim Tel +82-53-420-4910 Fax +82-53-422-9195 E-mail
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 ( 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
Vol.28, No.3, August 2019: 211-220
212 |Juyoung Kim Nutritional Supplement and Athletic Performance
Vol.28, No.3, August 2019: 211-220
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.
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
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].
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
at troponin C and delayed Ca
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
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
214 |Juyoung Kim Nutritional Supplement and Athletic Performance
Vol.28, No.3, August 2019: 211-220
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].
Juyoung Kim Nutritional Supplement and Athletic Performance| 215
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
216 |Juyoung Kim Nutritional Supplement and Athletic Performance
Vol.28, No.3, August 2019: 211-220
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].
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
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.
No potential conf lict of interest relevant to this article was reported.
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... Therefore, coaches, trainers, and players are interested in various factors for optimizing performance in soccer games, especially apparel, footwear, training, diets, and ergogenic aids that can help improve and maintain player performance in a game [5,6]. Among them, ergogenic aids are useful tools that can be utilized for improving performance in sports [7]. Through a consensus statement, the International Olympic Committee (IOC) recently presented few ergogenic aids that have adequate level of scientific evidence and are safe and effective with respect to performance gains by athletes. ...
... As is well known, sodium bicarbonate supplementation is proposed because of the relationship between exercise-induced acidosis and fatigue [15]. ATP hydrolysis and glycolysis can improve anaerobic performance in soccer because they alleviate metabolic acidosis by removing H+ in cells [7,15]. ...
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Creatine and sodium bicarbonate are both ergogenic aids for athletic performance. However, research on the combined creatine and sodium bicarbonate (CSB) supplementation in soccer is limited. This study investigated the changes in soccer-specific performance in elite soccer players after supplementing with CSB. Twenty well-trained elite soccer players participated in the study (age: 20.70 ± 1.08 years; height: 173.95 ± 2.81 cm; body weight: 70.09 ± 3.96 kg; soccer experience: 8 years; average training hours per week: 20 h). The participants were randomly allocated into CSB groups (CSB, n = 10) and placebo groups (PLA, n = 10). The CSB group took creatine (20 g/day) and sodium bicarbonate (0.3 g/kg/day); these two supplements were taken four times a day (morning, afternoon, evening, and before sleep) for seven days. Soccer-specific performance was assessed via 10- and 30-m sprint, coordination, arrowhead agility, and Yo-Yo intermittent recovery level 1 tests. Compared to the PLA group, the CSB group performed better in the 30-m sprint (CSB: −3.6% vs. PLA: −0.6%, p = 0.007, effect size (ES): 2.3) and both right and left arrowhead agility (right: CSB: −7.3% vs. PLA: −0.7%, p < 0.001, ES: 2.8; left: CSB: −5.5% vs. PLA: −1.2%, p = 0.001, ES: 2.1) tests. However, there were no differences in 10 m sprints, coordination, and Yo-Yo intermittent recovery level 1 tests between the two groups (p > 0.05). In conclusion, CSB supplementation improved sprint and agility in elite soccer players. However, it is still unclear whether such effect is synergistic effect of two supplements or the result of either one of them. Therefore, caution should be taken when interpreting the results, and the limitations should be examined further in future studies.
... The framework was developed based on scientific evidence, safety, legality, and effectiveness in improving sports performance. It classifies nutritional supplements into four groups, A, B, C, and D, which are used to develop recommended best practice protocols for athletes [8]. However, supplements may contain undeclared doping substances that are banned by many sports associations. ...
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The lack of specific recommendations on the use of supplements for sport climbers may be the reason for their misuse by athletes of this discipline. This study aimed to evaluate choices of dietary supplementation, the reasons for taking them, and the source of information on supplementation among sport climbers at different levels. In addition, how climbers subjectively evaluated the impact of their diets in supporting selected aspects of climbing training was evaluated. We enrolled 110 regular sport climbers (40 women and 70 men) from Wroclaw, Poland, who completed a validated questionnaire, assessing their use of dietary supplements, attitudes towards the influence of diet on sports performance, and climbing level. Their anthropometric measurements were also collected. Participants regarded diet as an important element of sports performance. Sport climbers indicated the Internet to be the main source of information on supplements. Health maintenance and improvement of recovery were the most frequently chosen reasons for taking dietary supplements. The most common supplements were isolated protein, vitamin C, vitamin D, magnesium, and amino acid blends. However, participants rarely used supplements suggested as beneficial for sport climbing performance. Therefore, developing recommendations for supplementation in sport climbing and promoting this should be an elementary part of the preparation for climbing training.
... There are also supplements such as beetroot juice, caffeine, and glycerol, which are said to boost performance and help the body cope with the demands of marathon training. However, their effects vary among athletes and may depend on training content, physical condition and habits [64]. ...
Full-text available
Performance in different athletic activities has continued to improve over time, with some athletes from diverse parts of the world registering new world records from time to time. With stiff competition from athletes from different parts of the world, constant upgrading of sports science based approaches to training and competition are employed to achieve more success. However, some approaches used to improve sports performance may pose ethical concerns and may challenge sports as a concept of celebrating natural human abilities. This book chapter interrogates the factors associated with efforts towards improvement of performance in endurance sports events, with a specific focus on marathon races, and the future implications for training, competition, and the nature of sports. While the interplay between nature and nurture determines the unique psychophysiological responses to training and competition, technological exploits leading to advanced sports products coupled with favourable natural and/or manipulated internal (body) and external environmental conditions will ensure continued improvement in performance. However, there is a need to censor commercial interest as well as safeguard safety and the nature of sports as a medium to celebrate natural human abilities.
... Sodium bicarbonate is often recommended for performance enhancement of rowing athletes as well. It has similar functions to β-alanine (the ability to buffer H +) [33]. Hobson et al. [34] reported intake of 0.3 g/kg sodium bicarbonate enhanced the athletic performance. ...
Full-text available
Rowing is a high-intensity sport requiring a high level of aerobic and anaerobic capacity. Although good nutrition is essential for successful performance in a rowing competition, its significance is not sufficiently established. This review aimed to provide nutritional strategies to optimize performance and recovery in rowing athletes based on a literature review. Following the guidelines given in the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA), we performed web searches using online databases (Pubmed, Web of Science, Wiley Online Library, ACS Publications, and SciFinder). Typically, a rowing competition involves a 6-8-min high-intensity exercise on a 2000-m course. The energy required for the exercise is supplied by muscle-stored glycogens, which are derived from carbohydrates. Therefore, rowing athletes can plan their carbohydrate consumption based on the intensity, duration, and type of training they undergo. For effective and safe performance enhancement, rowing athletes can take supplements such as β-alanine, caffeine, β-hydroxy-β-methylbutyric acid (HMB), and beetroot juice (nitrate). An athlete may consume carbohydrate-rich foods or use a carbohydrate mouth rinse. Recovery nutrition is also very important to minimize the risk of injury or unexplained underperformance syndrome (UUPS) from overuse. It must take into account refueling (carbohydrate), rehydration (fluid), and repair (protein). As lightweight rowing athletes often attempt acute weight loss by limiting food and fluid intake to qualify for a competition, they require personalized nutritional strategies and plans based on factors such as their goals and environment. Training and competition performance can be maximized by including nutritional strategies in training plans.
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Exercise-induced muscle damage (EIMD) causes increased soreness, impaired function of muscles, and reductions in muscle force. Accumulating evidence suggests the beneficial effects of creatine on EIMD. Nevertheless, outcomes differ substantially across various articles. The main aim of this meta-analysis was to evaluate the effect of creatine on recovery following EIMD. Medline, Embase, Cochrane Library, Scopus, and Google Scholar were systematically searched up to March 2021. The Cochrane Collaboration tool for examining the risk of bias was applied for assessing the quality of studies. Weighted mean difference (WMD), 95% confidence interval (CI), and random-effects model, were applied for estimating the overall effect. Between studies, heterogeneity was examined using the chi-squared and I² statistics. Nine studies met the inclusion criteria. Pooled data showed that creatine significantly reduced creatine kinase (CK) concentration overall (WMD = −30.94; 95% CI: −53.19, −8.69; p = .006) and at three follow-up times (48, 72, and 96 hr) in comparison with placebo. In contrast, effects were not significant in lactate dehydrogenase (LDH) concentration overall (WMD = −5.99; 95% CI: −14.49, 2.50; p = .167), but creatine supplementation leaded to a significant reduction in LDH concentrations in trials with 48 hr measurement of LDH. The current data indicate that creatine consumption is better than rest after diverse forms of damaging and exhaustive exercise or passive recovery. The benefits relate to a decrease in muscle damage indices and improved muscle function because of muscle power loss after exercise. Practical applications Creatine supplementation would be effective in reducing the immediate muscle damage that happens <24, 24, 48, 72, and 96 hr post-exercise. In the current meta-analysis, the positive effects of creatine could cause a decrease in CK concentration overall. But, due to high heterogeneity and the medium risk of bias for articles, we suggest that these results are taken into account and the facts are interpreted with caution by the readers.
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Carbonates and bicarbonates are two groups of accelerators which can be used in sprayed concrete. In this study, the effects of the two accelerators sodium carbonate (Na₂CO₃) and sodium bicarbonate (NaHCO₃) (0%, 1%, 2%, 3%, and 4% by weight of ordinary Portland cement OPC) on the properties of OPC paste were compared. The results show that both of them could accelerate the initial and final setting time of OPC paste, but the effect of the two accelerators on the compressive strength were different. After 1 day, sodium bicarbonate at 3% had the highest strength while sodium carbonate at 1% had the highest strength. After 7 days, both of the two accelerators at 1% had the highest compressive strength. After 28 days, the compressive strength decreased with the increase of the two. The improved strength at 1 and 7 days was caused by the accelerated formation of ettringite and the formation of CaCO₃ through the reactions between the two with portlandite. The decrease of strength was caused by the Na⁺ could reduce the adhesion between C-S-H gel by replacing the Ca2+. NaHCO₃ was found be a better accelerator than Na₂CO₃.
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Background Theacrine (1,3,7,9-tetramethyluric-acid) is a pure alkaloid with a similar structure to caffeine and acts comparably as an adenosine receptor antagonist. Early studies have shown non-habituating effects, including increases in energy and focus in response to Teacrine®, the compound containing pure theacrine. The purpose of this study was to determine and compare the effects of Teacrine® and caffeine on cognitive performance and time-to-exhaustion during a simulated soccer game in high-level male and female athletes. Methods Male and female soccer players (N = 24; MAge = 20.96 ± 2.05y, MMaleVO2max = 55.31 ± 3.39 mL/O2/kg, MFemaleVO2max = 50.97 ± 3.90 mL/O2/kg) completed a 90-min simulated treadmill soccer match over four randomized sessions (TeaCrine®, caffeine, TeaCrine® + caffeine, placebo). Cognitive testing at halftime and end-of-game including simple reaction time (SRT), choice RT (CRT), and cognitive-load RT with distraction questions (COGRT/COGRTWrong) was performed, with a run time-to-exhaustion (TTE) at 85% VO2max following end-of-game cognitive testing. Session times and pre-exercise nutrition were controlled. RM-MANOVAs with univariate follow-ups were conducted and significance was set at P < 0.05. Results TTE trended towards significance in TeaCrine® and TeaCrine® + caffeine conditions compared to placebo (P < 0.052). A condition main effect (P < 0.05) occurred with faster CRT in caffeine and TeaCrine® + caffeine compared to placebo. COGRTWrong showed a significant time main effect, with better accuracy at end-of-game compared to halftime (P < 0.05). A time x condition interaction in SRT (P < 0.05) showed placebo improved from halftime to end-of-game. Conclusions The 27–38% improvements in TTE reflect increased performance capacity that may have important implications for overtime scenarios. These findings suggest TeaCrine® favorably impacts endurance and the combination with caffeine provides greater benefits on cognitive function than either supplement independently.
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β-Alanine supplementation is one of the world's most commonly used sports supplements, and its use as a nutritional strategy in other populations is ever-increasing, due to evidence of pleiotropic ergogenic and therapeutic benefits. Despite its widespread use, there is only limited understanding of potential adverse effects. To address this, a systematic risk assessment and meta-analysis was undertaken. Four databases were searched using keywords and Medical Subject Headings. All human and animal studies that investigated an isolated, oral, β-alanine supplementation strategy were included. Data were extracted according to 5 main outcomes, including 1) side effects reported during longitudinal trials, 2) side effects reported during acute trials, 3) effect of supplementation on circulating health-related biomarkers, 4) effect of supplementation on skeletal muscle taurine and histidine concentration, and 5) outcomes from animal trials. Quality of evidence for outcomes was ascertained using the Grading of Recommendations Assessment Development and Evaluation (GRADE) framework, and all quantitative data were meta-analyzed using multilevel models grounded in Bayesian principles. In total, 101 human and 50 animal studies were included. Paraesthesia was the only reported side effect and had an estimated OR of 8.9 [95% credible interval (CrI): 2.2, 32.6] with supplementation relative to placebo. Participants in active treatment groups experienced similar dropout rates to those receiving the placebo treatment. β-Alanine supplementation caused a small increase in circulating alanine aminotransferase concentration (effect size, ES: 0.274, CrI: 0.04, 0.527), although mean data remained well within clinical reference ranges. Meta-analysis of human data showed no main effect of β-alanine supplementation on skeletal muscle taurine (ES: 0.156; 95% CrI: −0.38, 0.72) or histidine (ES: −0.15; 95% CrI: −0.64, 0.33) concentration. A main effect of β-alanine supplementation on taurine concentration was reported for murine models, but only when the daily dose was ≥3% β-alanine in drinking water. The results of this review indicate that β-alanine supplementation within the doses used in the available research designs, does not adversely affect those consuming it.
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Studies have shown that creatine supplementation increases intramuscular creatine concentrations, favoring the energy system of phosphagens, which may help explain the observed improvements in high-intensity exercise performance. However, research on physical performance in soccer has shown controversial results, in part because the energy system used is not taken into account. The main aim of this investigation was to perform a systematic review and meta-analysis to determine the efficacy of creatine supplementation for increasing performance in skills related to soccer depending upon the type of metabolism used (aerobic, phosphagen, and anaerobic metabolism). A structured search was carried out following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines in the Medline/PubMed and Web of Science, Cochrane Library, and Scopus databases until January 2019. The search included studies with a double-blind and randomized experimental design in which creatine supplementation was compared to an identical placebo situation (dose, duration, timing, and drug appearance). There were no filters applied to the soccer players’ level, gender, or age. A final meta-analysis was performed using the random effects model and pooled standardized mean differences (SMD) (Hedges’s g). Nine studies published were included in the meta-analysis. This revealed that creatine supplementation did not present beneficial effects on aerobic performance tests (SMD, −0.05; 95% confidence interval (CI), −0.37 to 0.28; p = 0.78) and phosphagen metabolism performance tests (strength, single jump, single sprint, and agility tests: SMD, 0.21; 95% CI, −0.03 to 0.45; p = 0.08). However, creatine supplementation showed beneficial effects on anaerobic performance tests (SMD, 1.23; 95% CI, 0.55–1.91; p <0.001). Concretely, creatine demonstrated a large and significant effect on Wingate test performance (SMD, 2.26; 95% CI, 1.40–3.11; p <0.001). In conclusion, creatine supplementation with a loading dose of 20–30 g/day, divided 3–4 times per day, ingested for 6 to 7 days, and followed by 5 g/day for 9 weeks or with a low dose of 3 mg/kg/day for 14 days presents positive effects on improving physical performance tests related to anaerobic metabolism, especially anaerobic power, in soccer players.
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Background The ability to generate high levels of power is one of the key factors determining success in many sport disciplines. Although there are studies confirming ergogenic effects of caffeine (CAF) on different physical and mental abilities, much controversy remains about its influence on power. The main goal of this study was to assess the effects of caffeine supplementation on time under tension (TUT) and the number of performed repetitions (REP). The second objective was to determine the effects of CAF supplementation on power (P) and movement velocity (V) during the bench press movement. Additionally the authors evaluated whether CAF has a significant effect on velocity of the bar in the eccentric (ECC) phase (VEMEAN) of the bench press movement. Methods The study included 20 men (20–31 yrs., 87.3 ± 7.7 kg) with at least 2 years of experience in resistance training. The study participants were divided randomly into two groups: the supplemented group ingested caffeine before exercise (GCAF), while the control group was given a placebo (GCON). The exercise protocol consisted of performing the bench press movement with a load equal to 70%1RM with maximal possible velocity (X/0/X/0). The experimental sets were performed to momentary muscular failure. Results The repeated measures ANOVA between the GCAF and GCON groups revealed statistically significant differences in 2 variables. Post-hoc tests demonstrated statistically significant differences in TUT when comparing the group supplemented with caffeine (13.689 s GCAF) to the one ingesting a placebo (15.332 s GCON) at p = 0.002. Significant differences were also observed in mean velocity during the eccentric phase of movement (0.690 m/s in the GCAF to 0.609 in GCON with p = 0.002). There were no significant differences in generated power and velocity in the CON phase of the movement between the GCAF and GCON. Conclusions The main finding of the study is that CAF ingestion increases movement velocity of the bar in the eccentric phase of the movement, what results in shortening of the time under tension (TUT) needed for performing a specific number of repetitions, without decreasing power and velocity in the CON phase of the movement.
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Human MondoA requires glucose as well as other modulatory signals to function in transcription. One such signal is acidosis, which increases MondoA activity and also drives a protective gene signature in breast cancer. How low pH controls MondoA transcriptional activity is unknown. We found that low pH medium increases mitochondrial ATP (mtATP), which is subsequently exported from the mitochondrial matrix. Mitochondria-bound hexokinase transfers a phosphate from mtATP to cytoplasmic glucose to generate glucose-6-phosphate (G6P), which is an established MondoA activator. The outer mitochondrial membrane localization of MondoA suggests that it is positioned to coordinate the adaptive transcriptional response to a cell’s most abundant energy sources, cytoplasmic glucose and mtATP. In response to acidosis, MondoA shows preferential binding to just two targets, TXNIP and its paralog ARRDC4. Because these transcriptional targets are suppressors of glucose uptake, we propose that MondoA is critical for restoring metabolic homeostasis in response to high energy charge.
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This study was designed to investigate the effects of β-alanine (BA) supplementation on peak power, power drop, and lactate response in elite male amateur boxers. Nineteen male Korean national team boxers were divided into groups with either BA (n=9) or placebo (PL, n=10) supplementation. BA consumed 4.9-5.4 g/day of BA with training for 10 weeks and PL took PL in a similar manner. Physical fitness and lactate changes in sparring were measured before and after the 10-week inter-vention. Significant interactions (P < 0.05) were shown for lower body peak power (P=0.049) and upper body power drop (P=0.042). Positive effects for the BA group were shown for lower body peak power (Co-hen d=0.72; 95% confidence interval [CI], 0.09-1.35) and the mainte-nance of upper body power output (d=-0.91; 95% CI, -1.61 to -0.17). These findings suggest that Korean national amateur boxers who con-sumed BA demonstrated differential responses following a training in-tervention in specific physical fitness when compared to boxing ath-letes who consumed a PL.
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As a nitric oxide precursor, beetroot juice (BJ) is known to enhance high-intensity exercise performance (80-100% VO 2max) yet its impacts on higher intensity sprint exercise (>100% VO 2max) remain to be established. This study sought to examine the effects of BJ supplementation on performance and subsequent fatigue during an all-out sprint exercise. Using a randomized cross-over, double-blind, placebo-controlled design, 15 healthy resistance-trained men (22.4 ± 1.6 years) ingested 70 mL of either BJ or placebo. Three hours later, participants undertook a 30-s all-out Wingate test. Before and after the sprint exercise and at 30 s and 180 s post-exercise, three countermovement jumps (CMJ) were performed and blood lactate samples were obtained. Compared to placebo, BJ consumption improved peak (placebo vs. BJ, 848 ± 134 vs. 881 ± 135 W; p = 0.049) and mean (641 ± 91 vs. 666 ± 100 W; p = 0.023) power output and also reduced the time taken to reach W peak in the Wingate test (8.9 ± 1.4 vs. 7.3 ± 0.9 s; p = 0.003). No differences were detected in the fatigue index. In addition, while over time CMJ height and power diminished (ANOVA p < 0.001) and blood lactate levels increased (ANOVA p < 0.001), no supplementation effect was observed. Our findings indicate that while BJ supplementation improved performance at the 30-s cycling sprint, this improvement was not accompanied by differences in fatigue during or after this type of exercise.
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Background: Sports nutrition is a constantly evolving field with hundreds of research papers published annually. In the year 2017 alone, 2082 articles were published under the key words 'sport nutrition'. Consequently, staying current with the relevant literature is often difficult. Methods: This paper is an ongoing update of the sports nutrition review article originally published as the lead paper to launch the Journal of the International Society of Sports Nutrition in 2004 and updated in 2010. It presents a well-referenced overview of the current state of the science related to optimization of training and performance enhancement through exercise training and nutrition. Notably, due to the accelerated pace and size at which the literature base in this research area grows, the topics discussed will focus on muscle hypertrophy and performance enhancement. As such, this paper provides an overview of: 1.) How ergogenic aids and dietary supplements are defined in terms of governmental regulation and oversight; 2.) How dietary supplements are legally regulated in the United States; 3.) How to evaluate the scientific merit of nutritional supplements; 4.) General nutritional strategies to optimize performance and enhance recovery; and, 5.) An overview of our current understanding of nutritional approaches to augment skeletal muscle hypertrophy and the potential ergogenic value of various dietary and supplemental approaches. Conclusions: This updated review is to provide ISSN members and individuals interested in sports nutrition with information that can be implemented in educational, research or practical settings and serve as a foundational basis for determining the efficacy and safety of many common sport nutrition products and their ingredients.
Dittrich, N, Serpa, MC, Lemos, EC, De Lucas, RD, and Guglielmo, LGA. Effects of caffeine chewing gum on exercise tolerance and neuromuscular responses in well-trained runners. J Strength Cond Res XX(X): 000-000, 2019-This study aimed to investigate the effects of caffeinated chewing gum on endurance exercise, neuromuscular properties, and rate of perceived exertion on exercise tolerance. Twelve trained male runners (31.3 ± 6.4 years; 70.5 ± 6.6 kg; 175.2 ± 6.2 cm; 9.4 ± 2.7% body fat; and V[Combining Dot Above]O2max = 62.0 ± 4.2 ml·kg·min) took part of the study. The athletes performed an intermittent treadmill test to determine maximal aerobic speed and delta 50% (Δ50%) intensity. In the following visits, they performed 2 randomized time to exhaustion tests (15.4 ± 0.7 km·h) after the ingestion of 300 mg of caffeine in a double-blind, crossover, randomized design. Maximal voluntary contraction of the knee extensor associated to surface electromyographic recording and the twitch interpolation technique were assessed before and immediately after the tests to quantify neuromuscular fatigue of the knee extensor muscles. Caffeine significantly improved exercise tolerance by 18% (p < 0.01). Neuromuscular responses decreased similarly after time to exhaustion in both exercise conditions; however, athletes were able to run a longer distance in the caffeine condition. The performance improvement induced by caffeine seems to have a neuromuscular contribution because athletes were able to run a longer distance with the same neuromuscular impairment.