The Influence of Nutritional Ergogenic Aids on Exercise ... · The Influence of Nutritional Ergogenic Aids on Exercise Heat Tolerance and Hydration Status Rebecca M. Lopez and Douglas

NUTRITION & ERGOGE,

The Influence of Nutritional Ergogenic Aids onExercise Heat Tolerance and Hydration StatusRebecca M. Lopez and Douglas J. Casa

Human Performance Laboratory, Department of Kinesiology, Neag School of Education, University ofConnecticut, Storrs, Connecticut

LOPEZ, R.M. and D.J. CASA. The influence of nutritional ergogenic aids on exercise heat tolerance and hydration status. Curr.S/xirts Med. Rep., Vol. 8, No. 4, pp- 192-199, 2009. Exercise in the heat may predispose an athlete to an exertional heat illness, h isimperative to be knowledgeahie on the influence of various nutritional supplements on exercise tolerance and hydration status. Because ofthe variety of nutritional ergogenic aids that are easily accessible to athletes, medical and health professionals must rely on empirical evidencewhen making conclusions about the efficacy of a supplement while not ignoring signißcant anecdotal reports that may resemble real'Ufe.situations mcïre closely.

INTRODUCTION

The use of supplements to improve athletic performancehas an extensive history by a wide range of competitiveathletes. Along with the proposed ergogenic effects ofnumerous supplements, which are often not proven or areexaggerated greatly, there could be harmful and potentiallyfatal side effects. Many athletes have a "win at all costs"mentality and will choose to use a supplement regardless ofthe possible side effects. Furthermore, many of the side effectsreported with supplements are anecdotal and have not beensupported by scientific evidence.

Exercise in the heat can have added risks to athletes.Recent exertional heat stroke tleaths have increased mediaattention to some supplements and their potential connec-tion with exertional heat stroke (7,15). Unfortunately, someof these reports and recommendations on the use of sup-plements are speculative and not based on factual evidenceor scientific research (7,55). As a result, athletes aremisinformed on which supplements may predispose them toan exertional heat illness. They are unaware what preven-tative measures to take when exercising in the heat. It isimperative that medical professionals educating athletes areknowledgeable about the various performance enhancers and

for correspondence: Rebecca M. Lopez, M.S., ATC, HFS, University ofConnecticut, Department of Kinesiology, 2CW5 Hillside Road, Uni[ 1110, Scorrs, CT06269-1110 (E-mail: Rchecca.Lopcî®uciinn.tdu).

1537-890X/0804/192-199Current Sports Medidni: ReportsCopyright © 2009 by the Ametican College of SporB Medicine

their possible effects on heat tolerance to be able to givesound recommendations to competitive athletes and otherphysically active populations. Randomized-control led trials(6,17,22,26,28,52,56,57) have resulted in evidence-hased rec-ommendations regarding the use of ergogenic supplements.Therefore, the purpose of this article is to describe the in-fluence of popular nutritional supplements on hydrationstatus and thermorégulation.

CREATINE

Although creatine was first identified in 1835, creatinesupplementation became increasingly popular in athleticpopulations in the 1990s (4). Creatine's popularity stemmedfrom research demonstrating an increase in skeletal musclephosphocreatine content and increased performance in somesubjects (55). Creatine is a dietary element found in meatand fish; however, creatine also is synthesized by the bodyand can be found in skeletal muscle, heart muscle, and otherorgans (27). Many athletes supplement with creatine becauseit has been shown to increase muscle concentrations of totalcreatine and phosphocreatine (32). This increase in creatineand phosphocreatine potentially can act as a source ofadenosine triphosphate in skeletal muscles, thereby increas-ing performance in short-duration, high-intensity lx>uLs ofexercise (55).

Initial reports on the efficacy and safety of creatine sup-plementation included warnings of possible long-term effectsof creatine and anecdotal reports of increased risk of heatillness and muscle injury (Figure; Table 1). In the late '90s,several media reports and scientific papers linked creatine to

192

-0.80 -0.60 -0.40 -0.20 0.00 0.20 0.40

Creatine-Placebo Difference (X)

Figure. Results of studies investigating the influence of creatine on hydration status and exercise heat tolerance. Reprinted from Lopez RM, ef al. Doescreatine suppiementation hinder exercise heat tolerance or hydration status: a systematic review with meta-analyses. J. Athl. Train. 2009;44:215-23.Copyright © 2009 National Athletic Trainers' Association. Used with permission. Citations pertain to references in the original artide.

several athletes' deaths (7,55). As a result, many havespeculated that individuals supplementing with creatine areat ijreater risk of heat illness when exercising in hot and/orhumid environments. In 2000, the American College ofSports Medicine's roundtable on creatine supplementationcautioned athletes on supplementing with creatine whileexercising in the heat (55). However, there was no evidenceat this time to support an Increased risk of an exertional heatillness as a result of creatine supplementation. Theseanecdotal claims resulted in an increase in scientific studies

TABLE 1. Nutritional ergogenic supplements: evidence of effectson heat tolerance and hydration status.

Putported Effects Evidence

Creatine increases bixiy mass ft

impairs hydration status J

Impairs thermorégulation Ji

Increases risk of EHI ?

Caifeine Mild diuretic at rest It

Dehydration during exercise ^

exacerbated

Impedes thermorégulation tt

Increases risk of EHI î

Glycerol Improves ability to retain fluids during ftendurance events

Improves physiological function when ^ in •athletes have access to fluids

Improves performance when athletes *»have access to fluids

Ephedra Impedes thermorégulation î

Increases ri.slc of EHI '

^ - No supporting evidence,to support, ' = Unknííwn.

EHI = cxertLonal heat injury

= Mixed results, ft = Existing evidence

investigating the relationship hetween creatine and hydra-tion status and/or heat intolerance (12,14,20,26,29,30,41,48,51,56,57,59,61,62). A systematic review ofthe exist-ing literature on the influence of creatine on thermorég-ulation and hydration .status concluded that there is noevidence to support claims that creatine impedes heat toler-ance or hydration status (35). As Table 2 illustrates, the sys-tematic review failed to show significant differences in hodytemperature between the creatine and placeho groups whileexercising in the heat.

The most common side effect from creatine supplementa-tion is increased hody mass as a result of water retention.This weight gain has heen hypothesized to affect the body'sability to thermoregulate by altering hody fluid balance. Re-searchers investigating the effect of creatine on body fluidbalance have had varying results. One study found that 10 dof creatine supplementation did not result in altered fluiddistribution or promote an osmotic fluid shift hetween fluidcompartments (14). Several studies found that supplement-ing with creatine increases total body water (20,29,30,48,56,59,61,62) and intracellular water (30,59,62), yet othershave found increases in extracellular water as well (20,59).This increase in total body water is evident in subjects whohave an increased body mass post-supplementation. How-ever, this influence of a possible fluid shift has not had anydetrimental effects on subjects' ability to dissipate heat whenexercising in the heat. Several studies have found that sub-jects supplementing with creatine had a lower heart rate andcore body temperature (20,29,30) while exercising in theheat when compared witb placebo. Also, subjects supple-menting with creatine who already were dehydrated beforeexercising in the heat showed no signs of heat intolerancecompared with placebo (57).

Researchers have concluded that both long-term andshort-tenn creatine supplementation may have no effect ormay even be advantageous for athletes exercising in the heat(12,14,20,23.29,30,35,41,57,59,61). The evidence from therecent increase in controlled studies does not support pre-vious claims that creatine may hinder heat tolerance and/or

Volume 8 • Number 4 • July/August 2009 The Influence of Nutritional Ergogenic Aids on EHT and Hydration Status 193

r

TABLE 2 . Results of studies investigating the influence of ereatine on hydration status and exercise heat tolerance."

Study

Eastonetal. {2007) (20)

Kern et ai. (2001) (29)

Kilduff et ai. (2004) (30)

Mendel ei ai. (2005) (41)

Volekeiol, (2001) (56)

Watson et ai, (2006) (57)

Weiss e( ai. (2006) (59)

Wright et fli. (2007) (61)

Overall

Mean

39.2

38.25

39.25

38.1

38.57

39.4

38.44

38.07

Great i ne

SD

0.5

0.35

0.4

0.4

0.07

0.4

0.42

0.47

Group

Participants

12

9

II

8

10

12

12

10

84

Mean

39.05

38.45

39.5

38.4

38.39

39.3

38.42

38.04

Placebo Gr

SD

0.5

0.35

0.55

0.3

0.26

0.4

0.29

0.56

oup

Participants

11

10

10

8

10

12

12

10

83

Weighting Factot

6.40%

10.90%

6.30%

9.00%

38.70%

10.50%

12.9

5.30%

100.00%

Mean Difference (C'rciUine-Placebo)

(95% Confidence Interval)

0.15 {-0.26, 0.56)

-0.20 (-0.52, 0.12)

-0.25 (-0.66, 0.16)

; -0.30 (-0.65. 0.05)

' 0.18 (0.01, 0J5)

0.10 (-0.22. 0.42)

0.02 (-0.27.0.31)

0.03 (-0.42. 0.48)

0.03 (-0.07. 0.13)

Hetetogeneitv: X^ = 10.90, # = 7, / = 0.14, / = 36%, Test for overall effect Z = 0.56, P = 0.57.

"Adapted from Lope: R. et ai Does creatine supplemencation hinder exercise heat tolerence or hydration status: a systematic review with meta-analyses.} . Athl. Train. 2009; 44:215-23. Copyright © 2009 National Athletic Trainers' Association. Used with permission. |

Fixed-effects, inverse variance model. I

hydration status. In fact, some studies found that creatineresulted in a lowet body temperature than placebo whenexercising in the heat (29,30,41). Although the rationalebehind this has not been elucidated, perhaps the increasedtotal body water seen with creatine supplementation resultsin improved thermorégulation. Therefore, there is a lack ofevidence to support advising athletes who are supplementingwith creatine to avoid exercise in the heat (35).

CAFFEINE

Caffeine, or 1,3,7-trimethylximthine, is one of the mostwidely used drugs. Recently, there has been an increase incaffeine intake by athletes to improve athletic performance.Only low to moderate doses of caffeine (3-10 mgkg ') areneeded to bring about an ergogenie effect (18). Researchershave found that these nontoxic doses of caffeine improveathletic performance, particularly endurance exercise (18).Some evidence suggests that caffeine also may serve as anergogenie aid in high-intensity bouts of exercise (18).

Although caffeine is a popular drug among general andathletic populations alike, caffeine often has been linkedwith dehydration and/or heat intolerance (Table 1). Thetheory behind this could be attributed to caffeine's diureticeffect, the stimulation of the sympathetic nervous system, oran increase in resting metabiilic rate (5). As a result, athletessometimes are advised to abstain from caffeine while exercis-ing, particularly in the heat. Recent studies have sought todetermine whether there is evidence to support advisingathletes to abstain fVom caffeine because of hydration and/orthermoregulatory impairments (6,17,19,21,22,42,52,54)-

Studies have investigated the short- and long-term effectsof various levels of caffeine ingestion on hydration status andthermorégulation in thermoneutral, warm, and hot con-ditions (Table 3). A study inve.stigating the effects of acutecaffeine ingestion on thermorégulation and hody fluidbalance during prolonged exercise in a thermoneutral envi-ronment found no adverse effects of caffeine on body fluidbalance or thermoregulatory or metabolic responses (21).

194 Current Sports Medicine Reports

Following ingestion of 5 and 2.5 mgkg of caffeine at 2 and0.5 h of exercise, respectively, there were no significant dif-ferences in final rectal temperature, total water loss, sweatrate, rise in rectal temperature, and percent change in plasmavolume compared with placebo (21 ).

Similarly, another study examined the effects of 6 mgkg"of caffeine before exercise in high ambient temperatutes onhemodynamic and body temperature responses (54)- Thisstudy found significant increases in lactate and heart rateduring exercise as a result of caffeine; however, caffeine againhad no effect on body temperature during exercise. Severalother researchers have found similar results with acutecaffeine intake having no adverse effects on flu id-electrolytebalance (42,52), sweat rate (22,52), urine osmolality (22,52),or thermoregulatory responses (22,42,52) compared witbnon-caffeinated sports drinks or placebo.

Although most studies have investigated the effects ofacute or short-term caffeine ingestion, one study looking atthe effects of long-term caffeine intake on hydration foundlittle evidence to suggest that chronic caffeine intake maylead to dehydration or heat intolerance (6). Armstrong et al.examined the effects of three levels of caffeine consumptionon fluid-electrolyte balance and renal function. Althoughthis study supported previous findings that caffeine may actas a diuretic soon after consumption, urine volumes, serumosmolality, and all other hydration measures were similaramong all treatment groups on all days (6). Until this study,little was known ahout the effects of chronic caffeine con-sumption greater than 24 h on hydration status. Across 11 d,changes in caffeine dosage had no significant effect on bodymass or urinary indices (6). This study found no evidence tosuggest that athletes consuming moderate amounts of caf-feine (3-6 mgkg d ) are at greater risk of hypohydrationand/or heat intolerance while exercising (6 mg kg d for a70-kg individual is equivalent to the following intake perday: 4 cups of coffee (8 oz.), 10 cans of Coca-Cola (12 oz.),or 5 cans of Red Bull (8 oz-), for example). Furthermore,caffeine's influence as a mild diuretic likely is negated whenfluid status is compromised during exercise in the heat.

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TABLE 3 . Diuretic effect of caffeine, considering dose and volume of fluid consumed."

Gender, Protocol L">uration (h), ScenarioCaffeine

Dose (mg)Did Caffeine InduceSignificant Diuresis?

Volume of FluidConsumed (mL)' Reference

6 women and 6 men, 24 h, in a laboratoty

4 men and 2 women, 4 h, laboratory cycling

7 men, 62-64 min, treadmill walking with 22 kg load

19 men, 6 d, free-living

19 men, 16 h, post-EHT and free-living

8 men, 4 h, resting in laboratory

Male medical students, 4 h, at rest in laboratory

12 women, 3 h, resting in laboratory

15 men, î h, resting in laboratory


18 men, free-living, 24 H

9 men, 3 h pose-exercise rehydration, lying supine in laboratory

16 men and 3 women, 2 h, post-exercise

7 women and 3 men, 4 hd~ ' for 3 d, outdoor field sports


20 men, 11 d, free-living

20 men, 16 h, post—EHT and free-living




18 men, free-living, 24 h


8 males, 4 h, resting in laboratory

642

596

553

452''

452''

360^

300

300

mm

250

m245

240

226^

226^

180*

150

150

Uf*90*

Yes at rest and sleep

Yes at rest, no during exercise

No during exercise

No during free—living and sleep

No during daily activities and sleep

Yes at rest

No at rest

No at rest

No at rest

No at rest


Yes at rest

yes at rest

No during exercise and rest periods

Yes at rest

No during free-living and sleep


No at rest

No at rest

No at rest


No at rest

No at rest

3294

2560

200

1821-2247-d"'

2600

946-1419

*

240

480

250

2800

300

1958

380C^3967-d"'

750

207a-2384-d"'

3280

946-1419

240

480

2800

946-1419

946-1419

2230

U

3

8

24

9

19

18

4

16

26

14

12

25

3

8

24

19

18

16

24

24

"Reprinted from Armstrong L, et d. Caffeine, fluid-electrolyte balance, temperature regulation, and exercist-heat tolerance. Exerc. Spun. Sd. Rev. 2007;33:135-40. Copyright © 2007 Wolters Kluwer Health. Used with permission. Citations pertain to references in the original article.

Comparison of group mean values W caffeine vs water or placebo (P < 0.05) in controlled-randomized experiments.

'Some studies reported only fluid intake, others total water intake from food + fluid.

Multiple caffeine doses (compare with same study in other rows). i

• Data not reported.

EHT = exercise—heat tolerance test (90 min treadmill walking, î7.7°C).

Results of the various studies examining the effects of caf-feine on hydration status suggest that there is little evidenceto support the recommendations for exercising individuals toavoid caffeine, particularly when exercising in the heat.

GLYCEROL

Compared with rhe other nutritional supplements men-tioned in this review, glycerol is the only ergogenic supple-menr with purported heneficial effects on hydration statusand/or heat tolerance (Table 1). Researchers have inves-tigated various means of hyperhydrating athletes beforeexercise, particularly for endurance events where hydratingduring exercise can be difficulr. Hyperhydration with wateralone has resulted in increased urine output soon afteringestion, thus leading to ineffective hyperhyd ration. As aresult, several studies have investigated the effects of glycerol

ingestion with water to promote hyperhydration to decreasecardiovascular and thermoregulatory strain and improveexercise perfonnance (3,24,25,28,31,36,38,40,44,46,49,60).A metaanalysis on the effects of glycert)l-induced hyper-hydration on fluid retention and exercise performancerevealed that hyperhydration with glycerol improved fluidretention by 50% compared to hyperhydration with wateralone (24). Glycerol is a naturally occurring three-carhonmolecule that increases the concentration of fluid in theblood and tissues (49). Increases in blood osmolality togetherwith increased water intake would result in an osmotic driveresulting in water retention (49).

The available literature on the influence of glycerol onincreasing athletic performance and/or improving variousphysiological responses is inconclusive. Various researchershave found that hyperhydration with glycerol has improvedperfonnance significantly versus hyperhydration with wateralone (25,28,44). However, others have found no significant


M

differences in exercise perfonnance when subjects were hy-perhydrated with glycerol (28,36,38,60). Data regarding theinfluence of giycerol on cardiovascular, theimoregulatory, andother physiologic responses also have varied. While somestudies have found decreases in cardiovascular and/or themio-regulatory strain with glycerol ingestion (25,28,38,44,46,60),others have found no significant differences between glyceroland placebo (31,38).

Studies investigating the effects of glycerol ingestionhefore exercise in the heat also varied in the results; how-ever, overall there were no definite advantages to glycerolover water in three out of these four studies (3,28,38,60).Anderson et a!, found that glycerol ingestion prior to 90 minof steady-state cycling resulted in fluid retention that wascapable of reducing cardiovascular strain and enhancingthermorégulation (3). Similarly, Kavouras et oí.'s findings ina rehydration study suggest that glycerol ingestion prior tocycling in the heat improved exercise capacity (28). Subjectsexercised 19% and 72% longer in the glycerol trial versusboth tbe water only and the non-fluid trials, respectively.However, despite increased cutaneous vascular conductanceand improved exercise capacity attributed to plasma volumeexpansion, there were no significant differences in urine out-put or other cardiovascular measures with glycerol comparedwith water or no fluid conditions (28).

In contrast to Anderson et ai.'s flndings, Marino et al.found no significant improvements in exercise perfonnancewith glycerol ingestion (38). Despite increases in sweat rateand urine osmolality in the glycerol condition compared withplacebo, a 60-min self-paced cycling bout in 34-5°C resultedin no decrease in thermoregulatory strain or increased per-formance. An investigation on the effects of pre-exerciseglycerol on performance and physiological function during amountain bike race in the heat found that glycerol withwater did not affect cardiovascular or thermoregulatory re-sponses compared with hydration without glycerol, despitedecreased urine output and water retention found withglycerol (60). Researchers also examined the effects of glyce-rol ingestion for both hyperhydration and as a rehydratingagent following 120 min of exercise-induced dehydra-tion. Results indicated the glycerol trial had significantlygreater fluid retention (approximately 700 mJL) compared withplacebt) (36).

The varying results in the literature could be attributedto differences in methodology, such as the time betweenglycerol hyperhydration and exercise. Studies with a greatergap between hyperhydration and exercise, such as 3 h post-glycerol, found approximately 600 mL greater total bodywater (34). Moreover, wben subjects were hyperhydratedpre-exercise and rehydrated during exercise, the hydrationadvantages of glycerol over water alone were lost. Similarly,when exercise start time was within 1 h of hyperhydration,there were no differences in hydration status between gly-cerol and water (34). Differences in exercise and hydrationprotocols also have been inconclusive. Therefore, the vari-ability in the literature makes it difficult to elucidate whetherhyperhydration with glycerol improves thermorégulation ordecreases cardiovascular strain during exercise, particularlywhile exercising in the heat. However, in certain situations(such as the inability to consume large amounts of fluid


during intense exercise in the heat or not having access tofluids), the use of preexercise glycerol may assist with main-taining hydration status during exercise.

EPHEDRA

The use of the supplement ephedra, from the Chineseplant species ma huang, has heen controversial in the lastdecade. Although the use of ephedra dates back more than5000 yr (1), only recently has the supplement been exposedas a potential performance enhancer and weight loss aid.Recent high-proflle athlete deaths have been linked to theuse of supplements such as ephedrine (7,15). Ephedrine isthe major isomer making up 30% to 90% oí the totalalkaloids found in ephedra (1); the other ephedra alkaloidsinclude pseudoephedrine, norpseudoephedrine, and methyl-ephedrine (2). Ephedra, often in combination with caffeine,has been associated with possibly predisposing athletes toexertional heat stroke, particularly with individuals exercis-ing in hot, humid environments (15,33).

As a result of speculations that ephedra is to blame forsome of these high-profile deaths, several sports organizationshave banned the use of ephedra for athletes. Several con-sumer health groups requested that the U.S. Ftxxl and DrugAdministration (FDA) ban the sale of ephedra-containingproducts, despite the lack of scientific evidence linkingephedrine to these reported deaths or serious side effects.Dietary supplements are regulated by tbe Dietary SupplementHealth and Education Act of 1994 (DSHEA); the FDAcan only ban a supplement if there is sufficient convincingevidence that the product is harmful (53). A review of 52randomized controlled trials investigating the effects ofephedra-containing dietary supplements on weight loss and/or athletic performance found there were no serious adverseevents, such as death or cardiovascular events; however,some ofthe side effects reported included anxiety, autonomiehyperactivity, palpitations, and headache (53). It could betheorized that increases in heart rate and metabolic rate as aresult of ephedra may lead to an increased heat load or someimpairment in the hody's ability to dissipate heat at the samerate that it is being generated. However, there has heen ntievidence of elevated core body temperature or heat intoler-ance in these randomized controlled trials (Table 1). Thesubjects used in these clinical trials, however, were healthyand had been screened for predisposing factors to illness.

There is a paucity of data regarding the potential influ-ence of ephedra-containing supplements on thermorég-ulation. Several studies have investigated the effects ofephedrine with caffeine (8-11,37), since many products onthe market contain both of these ingredients. However,many of these studies were examining the influence ofephedrine on exercise performance and did not report ther-moregulatory measures (8,10,11,45). One study hy Bell andassixiates examined the effects of caffeine and ephedrine(C+E) ingestion on thermal regulation during heat stresstrials in 40^C (9). Initial pre-exercise rectal temperatures( Tre) were not different, and changes in T^^ throughout theexercise bouts were not significantly different between C+Eand placebo conditions (9).

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There have, however, been several case studies linkingephedra to exertional heat stroke (15,47). The death of theBaltimore Orioles' pitcher Steve Bechler was linked initiallyto ephedrine supplements that he was taking when hecollapsed from exertional heat stroke (15). However, it hasbeen suggested that there were several other factors inBechler's case that may have either predisposed him to heatstroke {e.g.., history of heat illness, lack of acclimatization,and several layers of clothing) or contributed to his death(improper treatment). Therefore, ephedrine could not besolely responsible for his death (33).

Another case, of a highly trained infantry soldier, may bethe only case, to our knowledge, to report a concrete con-nection between ephedra and exertional heat stroke (47).Although the mechanism through which ephedra may causeexertional heat stroke is not immediately clear, it is believedthat ephedra may activate dopamine receptors and impairheat dissipation through vasoconstriction, thus pnjducing athermogenic effect (45). To date, there is insufficient evi-dence that ephedra can impair thermorégulation; however,the inability to conduct randomized controlled trials becauseof its potential negative effects may leave the effects ofephedra while exercising in the heat unknown. Furthermore,there have been sufficient case reports of deaths linked toephedra (whether heat-related or not) to make one wary ofsuggesting ephedra as a safe supplement for athletes or otherexercising individuals.

OTHER SUPPLEMENTS

With the abundance of supplements in the sports marketand the lack oí regulation by the FDA, it is not surprisingthat there are many unknowns regarding the effects of othersupplements on hydration and thermorégulation. There are afew other supplements that can be used as ergogenic aids andwarrant mention in this review with regard to their effect onhydration and/or thermorégulation. Although many studieshave investigated the effects of branched-chain amino acids(BCAA) on exercise performance, few have examined theeffect that BCAA supplementation may have on hydrationstatus and/or thermorégulation. Cheuvront et al. examinedthe impact of BCAA supplementation and performance inthe heat when hypohydrated (16). This study found thatexercise in the heat (40°C) after ingestion of either anisocaloric BCAA and carbohydrate drink or a carbohydrate-only drink resulted in no differences in core body temper-ature. Similarly, Mittleman et al. compared the effects of aBCAA drink to a placebo during exercise in the heat(34.4''C) and found no significant differences in core bodytemperature or sweat losses (43). In a study comparing theeffects of varying levels of protein Intake on hydration in-dexes, Martin et al. found that although plasma osmolalityand urine specific gravity were elevated as protein intakeincreased, these hydration indexes were still within normallimits (39). Therefore, the effect oí increased protein intakeon measures of hydration status was minimal.

The combination of several dietary supplements was alsobelieved to have caused a malignant hyperthermia reactionin an otherwise healthy trauma patient (13). A 24-yr-old

male trauma patient developed malignant hyperthermia afterreceiving the anesthetic sevoflurane in the operating room.The family denied a history of malignant hyperthermiaand heat/exercise intolerance; however, upon recovery thepatient admitted to 6 months of daily intense exercise, in-gestion of creatine monophosphate and Ripped Fuel* (con-taining caffeine, ephedrine, and aspirin), daily injections ofdeca-dunibolin (an anabolic steroid), and weekly testoster-one (13). Although the authors of this case study had severalhypotheses for the occurrence of malignant hyperthermia,the most prominent conclusion was that the patient mayhave increased intracellular calcium pharmacologically andaltered skeletal muscle metabolism, which combined withthe anesthetic may have contributed to the rapid malignanthyperthermia. Although the use of these supplements couldnot be confirmed as the cause of the hyperthermia, this casestudy epitomises the idea that the effects of combining un-controlled .supplements may be deleterious.

The effects of some prescribed medications on hydrationstatus and/or thermorégulation also warrant more randomizedcontrolled trials, particularly when combined with exercisein the heat. Recent studies on the effects of acute dopaminereuptake inhibition have demonstrated elevated tempera-tures during an exercise bout in the heat (50,58). Ingestionoí methylphenidate, a medication commonly prescribed tochildren and adults for the treatment of attention deficithyperactivity disorder (ADHD) resulted in increased exerciseperformance as well as increased core temperatures onlyin the warm condition (30°C) compared to a temperatecondition (lS^C) (50). The subjects' perceptual responsesof ratings of perceived exertion and thermal stress werenot influenced by the drug treatment (50). TTiis could bepotentially dangerous during intense exercise in the heat,as athletes taking this medication may be susceptible tobigher body temperatures while signals from the centralnervous system to decrease intet\sity or cease exercise may beinhibited.

CONCLUSION

Exercising in the heat can predispose an athlete to anexertional heat illness if preventative measures are notheeded. Given that supplements are easily available andthe veracity of their contents are tainted, it is imperative toremain abreast of the most recent evidence regardingsupplementation to better educate and advise athletes. Onealso must rely on empirical evidence when making con-clusions about the efficacy of a supplement while not ig-noring significant anecdotal reports that more closely mayresemble real-life situations. There continues to be an im-mense need for more randomized, controlled trials on theinfluence of nutritional supplements on hydration and ther-morégulation in order to determine their clinical applicationin the sports arena.

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Volume 8 • Number 4 • July/August 2009 The Influence of Nutritional Ergogenie Aids on EHT and Hydration Status 199

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The Influence of Nutritional Ergogenic Aids on Exercise ... · The Influence of Nutritional Ergogenic Aids on Exercise Heat Tolerance and Hydration Status Rebecca M. Lopez and Douglas