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Athletes engaged in heavy endurance training often seek additional nutritional strategies to help maximize performance. Specific nutritional supplements exist to combat certain factors that limit performance beginning with a sound everyday diet. Research has further demonstrated that safe, effective, legal supplements are in fact available for today’s endurance athletes. Several of these supplements are marketed not only to aid performance but also to combat the immunosuppressive effects of intense endurance training. It is imperative for each athlete to research the legality of certain supplements for their specific sport or event. Once the legality has been established, it is often up to each individual athlete to decipher the ethics involved with ingesting nutritional supplements with the sole intent of improving performance. Key wordsExercise–Nutrition–Endurance–Supplements–Ergogenics
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11 Nutritional Supplements
for Endurance Athletes
Christopher J. Rasmussen
Abstract
Athletes engaged in heavy endurance training often seek additional nutritional
strategies to help maximize performance. Specific nutritional supplements
exist to combat certain factors that limit performance beginning with a
sound everyday diet. Research has further demonstrated that safe, effective,
legal supplements are in fact available for today’s endurance athletes.
Several of these supplements are marketed not only to aid performance but
also to combat the immunosuppressive effects of intense endurance training.
It is imperative for each athlete to research the legality of certain supple-
ments for their specific sport or event. Once the legality has been established,
itisoftenuptoeachindividualathlete to decipher the ethics involved
with ingesting nutritional supplements with the sole intent of improving
performance.
Key words
Exercise Nutrition Endurance Supplements Ergogenics
1. INTRODUCTION
The endurance athlete has special nutritional needs that go above
and beyond those of the normal sedentary individual. To optimize
performance the endurance athlete needs a solid foundation that
includes proper training and nutrition. Proper training should be
based on the principles of training and largely depends on the goals
of the individual athlete and the point in time within the training
cycle (preseason, in-season, postseason). Proper nutrition should
focus on a variety of whole foods that adequately meet the demands
of the athlete. Supplementing the diet with additional nutrients is
From: Nutritional Supplements in Sports and Exercise
Edited by: M. Greenwood, D. Kalman, J. Antonio,
DOI: 10.1007/978-1-59745-231-1_11, ÓHumana Press Inc., Totowa, NJ
369
becoming increasingly important for those engaged in heavy endur-
ance training because it is often difficult to obtain the proper amount
of macronutrients through whole foods alone. This chapter largely
addresses the specific nutritional needs of the endurance athlete and
more specifically nutritional supplements for the endurance athlete.
Several studies have documented that endurance athletes can
improve their training sessions and performance with a combination
of proper everyday nutrition and effective supplementation (17).
To gain a better understanding of how supplementation can
improve performance for the endurance athlete it is important to
realize what drives their performance. Therefore, the chapter begins
with a description of the factors associated with optimal perfor-
mance of the endurance athlete and the factors that limit their
performance. The second section focuses on specific supplements
for endurance athletes and how they can prepare the athlete for
action and enhance the training response. The third section dis-
cusses how supplementation can aid the immune system to keep it
functioning during even the most intense phases of training. The
fourth section briefly dives into additional legal and ethical issues.
Finally, a brief summary reviews the most important points of the
chapter and brings it to a close.
2. FACTORS LIMITING ENDURANCE ATHLETIC
PERFORMANCE
Various types of training are utilized by endurance athletes
depending on whether they are aiming to improve anaerobic capa-
city, maximal aerobic power (MAP)—power output when VO
2
max
is reached—or endurance capability. It is important to point out
that the term ‘‘endurance athlete’’ in athletic circles today tradition-
ally refers to those participating in running, cycling, swimming, and/
or combinations of these activities, although other activities may
certainly be considered. Combinations of training including speed,
interval, tempo, resistive, and long slow distance (LSD) are common
for the endurance athlete. Manipulating the principles of training
depending on the overall goals while coinciding with the respective
training season helps optimize training and subsequent performance.
The nutritional supplements discussed in this chapter focus primarily
370 Rasmussen
on their effectiveness, or lack thereof, in athletes who are involved in
running, cycling, and/or swimming events.
Prior to discussing specific supplements for endurance athletes, it is
important to understand the factors that limit endurance performance.
Dehydration, the depletion of muscle glycogen, and limited blood
glucose availability can all play a role in fatigue during long-duration
aerobic exercise. The body transfers heat to the environment through
conduction, convection, radiation, evaporation, or a combination of
these methods. Conduction involves the transfer of heat from one
material to another through direct molecular contact, and convection
is the transfer of heat from one place to another by the motion of a gas
or a liquid across the heated surface. Radiation involves the dissipation
of heat in the form of infrared rays, and evaporation is best defined as
the evaporation of sweat from the skin’s surface.
Evaporation is the primary avenue for heat dissipation during
exercise, accounting for roughly 80% of the total heat loss during
exercise. With prolonged exercise or exercise in a hot and humid
environment, blood volume is reduced by a loss of water through
sweat. As exercise continues in a hot, humid environment, a redistribu-
tion of blood from the core to the periphery takes place to cool the
body. Cardiac filling is reduced as the total blood volume gradually
decreases with an increase in the duration of exercise. This leads to a
decrease in venous return to the right side of the heart. Subse-
quently, stroke volume is reduced. The heart rate then tries to
compensate for the decreased stroke volume by increasing in an
effort to maintain cardiac output. Collectively, these alterations are
referred to as the cardiovascular drift. The benefit of this phenom-
enon is that one is able to continue exercising at a low to moderate
intensity. The drawback is that the body is unable to compensate
fully for the decreased stroke volume at high exercise intensities
owing to the fact the heart rate attains its maximum value at a much
lower exercise intensity. A loss of body fluid equal to 1% of body
weight (approximately 2.0 lb for a 200 lb athlete) can significantly
reduce blood volume, placing undue stress on the cardiovascular
system and limiting physical performance (8).Whendehydration
reaches 4%, endurance athletes can experience heat cramps and
heat exhaustion (9); and when it reaches upwards of 6%, there may
be cessation of sweating, a rise in body temperature, and eventually
heat stroke (10).
Nutritional Supplements for Endurance Athletes 371
Collectively the depletion of muscle glycogen and the decline in
blood glucose can put a damper on endurance athletic performance.
Plasma fatty acids and muscle triglycerides are able to supply the
needed energy during low-intensity exercise (i.e., 25% VO
2
max) (11).
Carbohydrate use is relatively low and comes from blood glucose.
Exercise at lower intensities can be maintained for several hours
owing to the fact that the liver is able to continually supply glucose
to the working muscles. As the intensity of exercise increases, the
amount of carbohydrate necessary to keep pace with the increased
demand also increases. A combination of blood glucose and muscle
glycogen contributes a large percentage of the energy requirements
at moderate exercise intensities (i.e., 65% VO
2
max) (11). At the
beginning of exercise, muscle glycogen is the preferred fuel source;
but as these levels decline there is increased dependence on blood
glucose by the exercising muscles. Higher-intensity exercise (85%
VO
2
max) is performed at a level that promotes an even higher rate
of muscle glycogen breakdown and carbohydrate oxidation (11).
This results in an accelerated rate of lactic acid production and
ultimately accumulation in muscle and blood. Contrary to popular
belief, lactic acid and lactate—the scapegoats for the pain athletes
experience—are not responsible for all the ills for which they are
blamed (see sidebar: The Truth About Lactate). Higher-intensity
exercise represents the highest level an athlete can maintain for
approximately 60 minutes. At these high intensities, carbohydrate
oxidation accounts for more than two-thirds of the required energy,
with the remainder coming from a combination of plasma fatty
acids and intramuscular triglycerides. Given the fact that most
competitive endurance athletes often train and compete at a higher
intensity, it is easy to reason why the depletion of muscle glycogen
and subsequent decline in blood glucose can be such a deterrent to
endurance athletic performance. Maintaining adequate hydration
and energy supplies is therefore essential to the performance of the
endurance athlete.
2.1. The Truth About Lactate
Lactic acid and lactate are not the same compound. Lactate is any
salt of lactic acid that enters the blood during high-intensity efforts.
Recall that lactic acid is a by-product of glycolysis. Although most
372 Rasmussen
people believe that it is responsible for fatigue and exhaustion dur-
ing all types of exercise, lactic acid accumulates in muscle fibers only
during relatively brief high-intensity efforts. Athletes, and endur-
ance athletes in particular, have been told for years that the primary
reason they cannot ‘‘push’’ any more during intense exercise is that
lactic acid has built up in their muscles. This is not entirely true, and
there is evidence to disprove it. It is possible to experience muscle
fatigue while the lactic acid concentration in the muscle remains low.
Marathon runners, for example, may have near-resting lactic acid
levelsattheendoftheracedespitetheirexhaustion(12).Con-
versely, there can be an absence of fatigue when the lactic acid
concentration in the muscle is high. Exhausting isometric efforts
with the quadriceps, for example, can cause fatigue and ultimately
terminate the exercise. Minutes after completion the athlete can
once again produce the initial force despite the fact that the degree
of acidity in the muscles decreases to normal rather slowly. There-
fore, it is difficult to accept the idea that an increase in lactic acid
in the muscle causes fatigue as a high degree of acidity without
fatigue can be observed. Lactate can also serve as an important fuel
source by other tissues by converting it to pyruvate and oxidizing it
in the mitochondria. For example, during exercise lactate serves as
a significant fuel source for the heart (12). Therefore, the fatigue
experienced by the endurance athlete is largely caused by a combi-
nation of dehydration and inadequate energy supplies, not excess
lactic acid.
3. SUPPLEMENTS FOR ENDURANCE ATHLETES
To combat the damaging and depleting effects of intense endur-
ance training and further help the body respond to training, a well
planned diet and supplement strategy that meets energy intake needs
and incorporates proper timing of essential nutrients is vital. It is
important to differentiate between the two popular terms ‘‘supple-
ments’’ and ‘‘ergogenic aids’’ when discussing athletes and nutrition.
Although the two are often used interchangeably, there are subtle
differences. A nutritional supplement is usually thought of as some-
thing that completes or makes an addition to something else. On
the other hand, the scientific literature refers to substances that
Nutritional Supplements for Endurance Athletes 373
athletes use to help enhance performance as ergogenic aids or sports
ergogenics. The term ergogenic is derived from the Greek words ergon
(work) and gennan (to produce). Thus, an ergogenic usually refers to
something that produces or enhances work. To avoid confusion, this
chapter uses the two terms interchangeably, although specific clas-
sifications of the sports ergogenics are mentioned. Countless supple-
ments now exist for athletes of all kinds. This chapter addresses
the most popular nutritional supplements available to endurance
athletes today.
Nutritional ergogenic aids serve as the foundation for endurance
performance and primarily include the macronutrients and micro-
nutrients. Athletes that do not consume enough calories and/or do
not consume enough of the right type of calories may hinder training
adaptations and subsequent performance. However, athletes who
consume a well planned diet during training can help the body adapt
to training and more than likely notice improved performance.
Furthermore, maintaining a diet that is deficient of the essential
macronutrients over time may lead to a loss of body mass and muscle
mass, increased susceptibility to illness, and an increase in the symp-
toms associated with overtraining. Practicing good dietary habits on a
daily basis is essential to help optimize training adaptations and
subsequent performance.
Preexercise nutrition should consist largely of moderate to low
glycemic index (GI) foods/supplements (Table 1) that provide a
slow, sustained release of carbohydrates and protein necessary to
fuel a workout (see sidebar: What Is the Glycemic Index?). It gen-
erally takes about 4 hours for dietary carbohydrate to be digested
and begin to be stored as muscle and liver glycogen. Thus, preex-
ercise meals should be consumed about 4 to 6 hours prior to exercise
(13). Putting this into an average everyday scenario means that for
an athlete who trains in the afternoon breakfast is the most impor-
tant meal to top off muscle and liver glycogen levels. If the athlete
trains first thing in the morning, the meal the evening before is vital.
Recent research has also indicated that ingesting a light carbohy-
drate and protein snack 30 to 60 minutes prior to exercise (e.g., 50 g
carbohydrate and 5–10 g protein) further increases carbohydrate
availability toward the end of an intense exercise bout owing to
the slight increase in glucose and insulin levels (14,15). This can
serve to increase the availability of amino acids and decrease
374 Rasmussen
Table 1
Partial list of the glycemic index of foods using glucose as the standard
Low GI Moderate GI High GI
Food GI Food GI Food GI
Chana dal 8 Apple juice 40 Life Savers
TM
70
Peanuts 14 Snickers
TM
41 White bread 70
Plain yogurt 14 Peach 42 Bagel 72
Soy beans 18 Pudding 43 Watermelon 72
Rice bran 19 Pinto beans 45 Graham
crackers
74
Peas 22 Orange juice 46 French fries 75
Cherries 22 Baked beans 48 Total
TM
76
Barley 25 Strawberry jam 51 Vanilla wafers 77
Grapefruit 25 Sweat potato 54 Gatorade
TM
78
Kidney beans 27 Pound cake 54 Fava beans 79
Link sausages 28 Popcorn 55 Jelly beans 80
Black beans 30 Brown rice 55 Tapioca
pudding
81
Lentils 30 Fruit cocktail 55 Rice cakes 82
Butter beans 31 Pita bread 57 Team Flakes
TM
82
Soy milk 31 PowerBar
TM
58 Pretzels 83
Lima beans 32 Honey 58 Corn Chex
TM
83
Skim milk 32 Blueberry
muffin
59 Corn flakes
TM
84
Split peas 32 Shredded wheat 62 Baked white
potato
85
Fettucini 32 Black bean
soup
64 Mashed
potatoes
86
Chickpeas 33 Macaroni and
cheese
64 Dark rye 86
Peanut
M&M’s
TM
33 Raisins 64 Instant rice 87
Chocolate milk 34 Canteloupe 65 Crispix
TM
87
Vermicelli 35 Mars Bar
TM
65 Boiled Sebago 87
Whole wheat
spaghetti
37 Rye bread 65 Rice Chex
TM
89
(Continued )
Nutritional Supplements for Endurance Athletes 375
exercise-induced protein catabolism (1416). Insulin inhibits protein
degradation and apparently offsets the catabolic effects of other
hormones (e.g., cortisol) (17). Anabolic actions of insulin appear
to be related to its nitrogen-sparing effects and promotion of nitro-
gen retention (17). The choice of foods and supplements selected is
largely up to individual athlete and their personal preferences. It is
recommended that the endurance athlete consume something famil-
iar on the day of competition rather than experimenting with a new
food or supplement.
3.1. What Is the Glycemic Index?
The glycemic index (GI) is a ranking of foods based on their
postprandial blood glucose response compared to a reference
food, either glucose or white bread. The GI concept was first devel-
oped in 1981 to help determine which foods were best for people
with diabetes. The GI of a food is based on several factors, including
the physical form of the food, the amylose/amylopectin ratio (two
types of starch), sugar content, fiber content, fat content, and the
acidity of a food. The index consists of a scale from 0 to 100 with 0
Table 1
(Continued)
Low GI Moderate GI High GI
Food GI Food GI Food GI
Apple 38 Pineapple 66 Gluten-free
bread
90
Pear 38 Grapenuts
TM
67 Baked red
potato
93
Tomato soup 38 Angel food cake 67 French
baguette
95
Ravioli 39 Stoned wheat
thins
67 Peeled Desiree 101
Pinto beans 39 Taco shells 68 Dates 103
Plums 39 Whole wheat
bread
69 Tofu frozen
dessert
115
GI, glycemic index
376 Rasmussen
(water) representing the lowest ranking and 100 (pure glucose) the
highest ranking. The GI is obtained through use of an oral glucose
tolerance test (OGTT) utilizing 50 g of carbohydrate from the test
food. Blood samples are then obtained periodically throughout a
2-hour time period, glucose levels are measured, and the area under
the curve is calculated (18).
The GI of a carbohydrate has a profound effect on subsequent
glucose and insulin responses. High-GI carbohydrates (i.e., dex-
trose, maltose) produce large increases in glucose and insulin levels.
Moderate-GI carbohydrates (i.e., sucrose, lactose) traditionally
produce only modest increases in glucose and insulin. Finally, low-
GI carbohydrates (i.e., fructose, maltodextrin) have little if any
effect on glucose and insulin responses. It has been suggested that
manipulating the GI of a sports supplement may optimize carbohy-
drate availability for exercise, particularly prolonged intense exer-
cise. Caution should be used when applying the GI to whole foods
that contain several ingredients. The GI is more accurate for indivi-
dually packed foods/supplements because of the fewer ingredients
and the standardization that exists with the processing of these
snacks/supplements. The GI is not as applicable to whole foods/
meals and has not been established for many of these whole foods/
meals.
Nutrition during an intense endurance training session can aid
in the quality of the workout especially if the workout exceeds 60
to 90 minutes. Nutrition during exercise for the endurance athlete
usually centers on supplementation more than pre- and postexercise
nutrition if for no other reason than the convenience supplements
provide. Convenience supplements include glucose-electrolyte solu-
tions (GES), meal replacement powders (MRPs), ready-to-drink
supplements (RTDs), energy bars, energy gels, and fitness waters.
They are typically fortified with various amounts of vitamins and
minerals and differ on the amount of carbohydrate, protein, and fat
they contain. The beneficial effects of solid and liquid carbohydrate/
protein supplements are similar when thermal stress is not a factor.
Liquid supplements do provide the added benefits of aiding
rehydration and tend to digest easier for most athletes while exercis-
ing. Cyclists can generally empty from the stomach up to 1000 ml of
fluid per hour, and therefore 40 to 60 g of carbohydrate can be easily
ingested while consuming a large volume of fluid (19). On the other
Nutritional Supplements for Endurance Athletes 377
hand runners generally consume less than 500 ml of fluid per hour
(20). This is because of the difficulty of drinking on the run and the
potential discomfort of running with a full stomach. Therefore,
runners tend to use more concentrated solutions than do cyclists in
order to consume adequate amounts of carbohydrate. For cyclists, a
carbohydrate solution of 4% to 6% is generally sufficient when fluid
replacement is important. For runners, this concentration may have
to be 8% to 10% to provide adequate carbohydrate. Glucose con-
centrations in excess of 10% seem to delay gastric emptying and
compromise fluid replacement (Fig. 1). Adequate sodium intake is
also important to combat potential electrolyte imbalances during
exercise. Most GES solutions contain sufficient quantities of
sodium. If sodium is lacking in the supplement, however, electrolyte
tablets (i.e., Heat Guard) are also available. The bottom line is that
rapid nutrient availability is especially important during a workout
to maintain energy levels and training intensity. Thus, high-GI
sources should make up most of the supplements ingested during
an endurance-type workout. Once again, athletes should experiment
with different formulations to find the one that works best for them
prior to competition.
Fluid
CHO
0.0
0.2
0.4
0.6
0.8
1.0
1.2
024681012141618
CHO GASTRIC EMPTYING (g/min)
% CHO CONCENTRATION OF SUPPLEMENT
4
5
6
7
8
9
10
11
12
FLUID GASTRIC EMPTYING (ml/min)
Fig. 1. Effect of carbohydrate (CHO) concentration on the rate of gastric
emptying of fluids and carbohydrate from the stomach during exercise. Car-
bohydrate concentrations of 8% to 10% maximize carbohydrate gastric emp-
tying without substantially reducing fluid delivery. From Gisolfi and Lamb
(100), with permission.
378 Rasmussen
It is now well established that with prolonged continuous exercise
the time-to-fatigue at moderate submaximum exercise intensities is
related to preexercise muscle glycogen concentrations—thus the
importance of everyday nutrition along with preexercise nutrition
(21). In addition, a GES has been the recommended supplement of
choice for decades during exercise to preserve muscle glycogen and
maintain blood glucose levels. With short-term, high-intensity exer-
cise, the relation between the availability of muscle glycogen and
performance is less clear. One study that utilized 15 high-intensity
6-second bouts on a cycle ergometer concluded that a high carbohy-
drate regimen over 48 hours helped subjects maintain a higher
power output than did the exercise and dietary regimen that
included a low carbohydrate content (22). This study demonstrated
the importance of a high carbohydrate diet in relation to short-term,
high-intensity exercise.
Recent research has shown that the addition of protein can have
added benefits to a supplement ingested during exercise by reducing
muscle protein degradation and speeding postexercise recovery.
Carbohydrate and protein intake significantly alters circulating
metabolites and the hormonal milieu (i.e., insulin, testosterone,
growth hormone, cortisol) as well as the response of muscle protein
and glycogen balance (23). Furthermore, the addition of protein
to a carbohydrate supplement enhances the insulin response of a
carbohydrate supplement compared to a placebo (24), which can
ultimately lead to performance gains (25).
Saunders et al. (7) examined the effects of a carbohydrate-
protein beverage on cycling endurance and muscle damage. They
utilized 15 male cyclists who were randomly administered either a
carbohydrate or carbohydrate-protein beverage (4:1 ratio) every
15 minutes during exercise and immediately upon completion of a
ride to volitional exhaustion. The carbohydrate-protein beverage
produced significant improvement in time-to-fatigue and reduction
of muscle damage in the selected endurance athletes. The authors
concluded that the benefits observed were the result of a higher total
caloric content of the carbohydrate-protein beverage or were due to
specific protein-mediated mechanisms.
Controversy exists among numerous studies examining the addition
of protein due to the fact that such addition increases the total caloric
content of the supplement. Anytime a larger amount of calories is
Nutritional Supplements for Endurance Athletes 379
consumed an athlete is likely to perform and recover more rapidly.
Therefore, when examining studies that are not based on isocaloric
data, one should give them careful consideration.
Whey is the preferred protein to ingest during exercise because of
its rapid absorption rates and the fact that is contains all of the
essential amino acids (refer to Table 3) as well as a high percentage
of leucine and glutamine, which are amino acids the body uses
during sustained exercise (26). High-GI carbohydrates (glucose,
sucrose, maltodextrin) should be combined with the protein in a
4:1 ratio to provide optimal benefits. Table 2 gives an example of the
ideal nutrient composition for a sports drink during exercise (27).
Sports drinks such as that shown in Table 2 should be ingested every
20 minutes during an endurance training session to help improve
performance and reduce muscle protein breakdown.
Postexercise nutrition for the endurance athlete is vital to restore
muscle glycogen stores, enhance skeletal muscle fiber repair and
growth, and maintain overall health and wellness. After an intense
exercise bout, the body is in a catabolic state (thus key muscle
Table 2
Ideal Nutrient Composition for a Sports Drink During Exercise
Nutrient objectives
Replace fluids and electrolytes
Preserve muscle glycogen
Maintain blood glucose levels
Maintain hydration
Minimize cortisol increases
Set the stage for a faster recovery
Satisfy thirst
Ideal composition (per 12 oz water)
High-glycemic carbohydrates (e.g., glucose, sucrose, maltodextrin):
20–26 g
Whey protein: 5–6 g
Vitamin C: 30–120 g
Vitamin E: 20–60 IU
Sodium: 100–250 mg
Potassium: 60–120 mg
Magnesium: 60–120 mg
Adapted from Ivy and Portman (27), with permission
380 Rasmussen
nutrients are being broken down). However, the opportunity exists
to alter the catabolic state into a more anabolic hormonal profile
where the athlete begins to rebuild muscle and thus initiates a much
faster recovery. Exercise that results in glycogen depletion activates
glycogen synthase, the enzyme responsible for controlling the trans-
fer of glucose from UDP-glucose to an amylase chain (28,29). This
also happens to be the rate-limiting step of glycogen formation. The
degree of glycogen synthase activation is influenced by the extent of
glycogen depletion (28). Complete resynthesis of muscle glycogen,
however, ultimately depends on adequate carbohydrate intake. Car-
bohydrates composed of glucose or glucose polymers are the most
effective for replenishing muscle glycogen, whereas fructose is most
beneficial for replenishing liver glycogen (30,31). Glucose and fruc-
tose are metabolized differently. They have different gastric empty-
ing rates and are absorbed into the blood at different rates (29,32).
Furthermore, the insulin response to a glucose supplement is gen-
erally much greater than that of a fructose supplement (33). The
fact that approximately 79% and 14% of total carbohydrate is
stored in skeletal muscle and the liver, respectively, is further indica-
tion of the importance of consuming glucose or glucose polymers
after exercise (13).
Blom et al. (34) found that ingestion of glucose and sucrose was
twice as effective as fructose for restoring muscle glycogen. The
maximum stimulatory effect of oral glucose intake on post-exercise
muscle glycogen synthesis was reached at a dose of 0.70 g/kg taken
every second hour following exercise in which the muscle glycogen
concentration was reduced by an average of 80%. In addition,
the rate of post-exercise muscle glycogen synthesis increases with
increasing oral glucose intake, up to a maximum rate of approxi-
mately 6 mmol/kg/hr. Blom et al. indicated that the differences
between glucose and fructose supplementation were the result of
the way the body metabolized these sugars. Fructose metabolism
takes place predominantly in the liver, whereas most glucose
appears to bypass the liver and is stored or oxidized by muscle (31).
Subsequent research by Burke and associates (35) found that the
intake of high-GI carbohydrate foods after prolonged exercise pro-
duces significantly more glycogen storage than consumption of low-
GI carbohydrate foods 24 hours after exercise. Although the meal
immediately after exercise elicited exaggerated blood glucose and
Nutritional Supplements for Endurance Athletes 381
plasma insulin responses that were similar for the low-GI and high-
GI meals, for the remainder of the 24 hours the low-GI meals elicited
lower glucose and insulin responses than the high-GI meals. As
previously mentioned, protein has shown additive effects to that of
carbohydrate alone in regard to the rate of muscle glycogen resynth-
esis and overall post-exercise recovery. The addition of protein to a
carbohydrate supplement increases insulin levels more than that
produced by carbohydrate or protein alone (36). Tarnopolsky
et al. showed that post-exercise carbohydrate and carbohydrate-
protein-fat nutritional supplements can increase glycogen resynth-
esis during the first 4 hours after exercise to a greater extent than
placebo for both men and women (37). The supplements adminis-
tered were both isoenergetic and isonitrogenous. Insulin has been
demonstrated to have profound anabolic effects on skeletal muscle.
In the resting state, insulin has been demonstrated to decrease the
rate of muscle protein degradation (38).
To summarize, in addition to the macronutrients selected, the
timing of nutrient ingestion can greatly affect the speed of recovery.
Research has clearly shown that muscle glycogen resynthesis occurs
more quickly if carbohydrate is consumed immediately following
exercise in contrast to waiting for several hours (39). Whereas most
of the everyday diet for the endurance athlete should be a low- to
moderate-GI diet, the post-exercise diet should be centered on mod-
erate- to high-GI sources. This nutritional approach has been found
to accelerate glycogen resynthesis and promote a more anabolic
hormonal state, which may speed recovery (37).
The increased protein and glycogen synthesis is believed to be due
to insulin secretion from the pancreas combined with an increase in
muscle insulin sensitivity (40). This was demonstrated in a study
(Fig. 2) showing that a carbohydrate-protein combination was
38% more effective in stimulating protein synthesis than a protein
supplement and more than twice as effective as a carbohydrate
supplement (41). Insulin appears to stimulate biosynthetic path-
ways that lead to increased glucose utilization, increased carbohy-
drate and fat storage, and increased protein synthesis. This metabolic
pattern is characteristic of the absorptive state. The rise in insulin
secretion during this state is responsible for shifting metabolic path-
ways to net anabolism (13). In contrast, when insulin secretion is
low, the opposite effect occurs. The rate of glucose entry into the
382 Rasmussen
cells is reduced and net catabolism occurs, rather than net synthesis
of glycogen, triglycerides, and protein. This pattern is reminiscent of
the postabsorptive state.
In addition to the major macronutrients, phosphorus, an essen-
tial mineral distributed widely in foods, may also be classified as
a nutritional sports ergogenic. Phosphorus is distributed widely in
foods, particularly meat, seafood, eggs, milk, cheese, whole-grain
products, nuts, and legumes. The Recommended Dietary Allowance
(RDA) is 800 mg for adults and 1200 mg for those 11 to 25 years of
age (42). Phosphate salts in both inorganic and organic forms play
important roles in human metabolism, particularly as related to
sports performance. They may influence all three human energy
systems by acting as intracellular buffers. Another theory suggests
that phosphate salts increase the formation of 2,3-diphosphoglycerate
(2,3-DPG), a compound in the red blood cells (RBCs) that facilitates
the release of oxygen to tissues.
An early study on phosphate loading examined highly trained
runners who took 1 g sodium phosphate four times daily for 6 days.
The phosphate salts increased the concentration of 2,3-DPG in
0
20
40
60
80
100
120
Protein Synthesis (mg/3 hr/leg)
Carbohydrate Protein Carb/Protein
Effect of Protein and Carbohydrate Alone and in Combination on Protein Synthesis Following
Exercise
Fig. 2. Effect of protein and carbohydrate alone and in combination on
protein synthesis, measured after exercise. From Tarnopolsky et al. (37),
with permission.
Nutritional Supplements for Endurance Athletes 383
RBCs by 6.6%, which subsequently resulted in an increase in
VO
2
max (43). This study also reported decreased production of
lactate and reduced sensation of physiological stress. A later study
utilizing highly trained crosscountry runners found that 1 g sodium
phosphate four times daily for 6 days resulted in a 10% increase in
VO
2
max and an 11.8% increase in the anaerobic threshold (5). The
authors attributed the improvements in exercise performance to
increased metabolic efficiency. Well controlled studies support the
theory that phosphate salt supplementation may enhance function
of the oxygen energy system. Furthermore, studies show that phos-
phate salt supplementation increases VO
2
max and improves perfor-
mance in endurance exercise tasks, including a greater number of
stages completed in a progressive treadmill running test, increased
time-to-exhaustion on a bicycle ergometer, and a decreased time to
complete a 40-km cycling test (42). However, if phosphate salts are
in fact ergogenic, the underlying mechanism has yet to be deter-
mined (42). The scientific literature suggests that phosphates may
have an ergogenic effect on endurance athletes, but there is little
support for its effectiveness during anaerobic exercise (44). More
research with tight methodological control is needed to support
claims made in regard to phosphorus supplementation in both
aerobic and anaerobic events.
Another popular nutritional ergogenic aid is the branched-chain
amino acids (BCAAs): leucine, isoleucine and valine. They are
prevalent in both protein/meal replacement powders and energy
drinks. Table 3 shows the typical amino acid composition of some
common protein preparations. The RDA for BCAAs is less than 3 g
per day, although supplementation studies frequently utilize 5 to
20 g per day in tablet form and 1 to 7 g per liter in solutions (42). The
theory behind BCAA supplements relates to a phenomenon known
as central fatigue, which holds that mental fatigue in the brain can
adversely affect physical performance in endurance events. The
central fatigue hypothesis suggests that low blood levels of
BCAAs may accelerate the production of the brain neurotransmit-
ter serotonin, or 5-hydroxytryptamine (5-HTP), and prematurely
lead to fatigue (45). Tryptophan, an amino acid that circulates in
the blood, is a precursor of serotonin and can be more easily
transported into the brain to increase serotonin levels when
BCAA levels in the blood are low because high blood levels of
384 Rasmussen
BCAAs can block tryptophan transport into the brain (46).Dur-
ing endurance exercise, as muscle and liver glycogen are depleted
for energy the blood levels of BCAAs also decrease, and fatty acid
levels increase to serve as an additional energy source (47).The
issue with extra fatty acids in the blood is that they need to attach
to albumin as a carrier protein for proper transport. In doing so,
the fatty acids displace tryptophan from its place on albumin and
facilitate the transport of tryptophan into the brain for conversion
to serotonin (48). Thus, the combination of reduced BCAAs and
elevated fatty acids in the blood causes more tryptophan to enter
the brain and more serotonin to be produced, leading to central
fatigue (49).
Table 3
Typical amino acid composition of whey, casein, and soy isolates
Amino acid Whey Casein Soy
Alanine 4.6 2.7 3.8
Arginine 2.3 3.7 6.7
Aspartic acid 9.6 6.4 10.2
Cysteine/cystine 2.8 0.3 1.1
Glutamic acid 15.0 20.2 16.8
Glycine 1.5 2.4 3.7
Histidine
a
1.6 2.8 2.3
Isoleucine
a,b
4.5 5.5 4.3
Leucine
a,b
11.6 8.3 7.2
Lysine
a
9.1 7.4 5.5
Methionine
a
2.2 2.5 1.1
Phenylalanine
a
3.1 4.5 4.6
Proline 4.4 10.2 4.5
Serine 3.3 5.7 4.6
Threonine
a
4.3 4.4 3.3
Tryptophan
a
2.3 1.1 1.1
Tyrosine 3.3 5.7 3.3
Valine
a,b
4.5 6.5 4.5
Values are expressed per 100 g of product
a
Essential amino acid
b
Branched-chain amino acid
Nutritional Supplements for Endurance Athletes 385
For endurance athletes competing in long races (more than 2 hours),
BCAA supplements can help delay central fatigue and maintain mental
performance (50). One study looked at BCAA supplementation dur-
ing a marathon and showed improved performance for slower runners
(3.05þhours) but no effect on faster runners (less than 3.05 hours) (2).
Chronic BCAA supplementation (2 weeks) has also been shown to be
effective in improving time-trial performance in trained cyclists (6).In
addition to their effects on prolonging endurance and delaying central
fatigue, BCAA supplements have been associated with a reduced rate
of protein and glycogen breakdown during exercise and an inhibition
of muscle breakdown following exhaustive endurance exercise (2,51).
A number of studies in trained and untrained subjects, however, have
shown no effect of BCAA supplements on exercise performance or
mental performance (52). In some cases, BCAAs have been compared
with carbohydrate supplementation during exercise, with results show-
ing they both delay fatigue to similar degrees (53). The data on BCAA
supplements are mixed, but they clearly do not harm endurance per-
formance. Some studies have shown positive adaptations, whereas
others have displayed no effect. Biological variations may determine
whether BCAAs are effective for the individual athlete and the parti-
cular sport or event.
Pharmacological sports ergogenics are drugs designed to func-
tion like hormones or neurotransmitter substances that are found
naturally in the human body. Like some nutritional sports ergo-
genics, pharmacological sports ergogenics may enhance physical
power by affecting various metabolic processes associated with
sport success. The most popular pharmacological sports ergogenics
used by endurance athletes today are caffeine and ephedrine.
Caffeine is theorized to enhance endurance performance by first
stimulating the central nervous system (CNS) and increasing psy-
chological arousal. Caffeine also stimulates the release of epinephr-
ine from the adrenal glad, which may further enhance physiological
processes such as cardiovascular function and fuel utilization. The
caffeine-mediated increase in free fatty acid mobilization and spar-
ing of muscle glycogen is the primary theory underlying the ergo-
genic effects of caffeine on prolonged endurance activities. Lastly,
caffeine increases myofilament affinity for calcium and/or increases
the release of calcium from the sarcoplasmic reticulum in skeletal
muscle, resulting in more efficient muscle contractions.
386 Rasmussen
In one of the first studies conducted on caffeine’s ergogenic effect,
subjects consumed decaffeinated coffee or decaffeinated coffee com-
bined with 330 mg pure caffeine 60 minutes prior to exercise. Time to
exhaustion was more than 19% longer in the caffeine trial than in
the decaffeinated trial (54). The authors concluded that the perfor-
mance increase was more than likely due to the increase in fat
oxidation as muscle glycogen was not measured. Another study
measured muscle glycogen utilization and found that caffeine prior
to exercise reduced muscle glycogen utilization by 30% (4). A later
study supported the muscle glycogen-sparing hypothesis by report-
ing a 55% decrease in muscle glycogenolysis during the first 15 min-
utes of exercise in the caffeine trial (55). The decrease in
glycogenolysis during the initial stages of exercise allowed more
glycogen to be available during the final stages, subsequently lead-
ing to an increased time to exhaustion. Further support of caffeine
supplementation was demonstrated in a study examining the effects
of acute caffeine ingestion (6 mg/kg) on prolonged, intermittent
sprint performance on a cycle ergometer. The total amount of sprint
work performed during the caffeine trial was 8.5% greater than that
performed during the placebo trial (56). The authors concluded
that acute caffeine ingestion can significantly enhance performance
of prolonged, intermittent sprint ability in competitive male, team-
sport athletes.
Despite the overwhelming ergogenic evidence of caffeine supple-
mentation, caution should be exercised when considering its use.
A recent study showed that in healthy volunteers a caffeine dose
corresponding to two cups of coffee (200 mg) significantly decreased
blood flow to the heart during exercise by 22%. That percentage
increased to 39% for people exercising in a high-altitude chamber,
which the researchers used to simulate the way coronary artery
disease (CAD) limits the amount of oxygen that gets to the heart
(57). Because an increase in blood to the heart is necessary for
aerobic activity, the findings theoretically suggest that caffeine
could slow the body down. The study’s purpose, however, was not
to look at whether caffeine could help athletes go faster or farther.
Instead, it set out to investigate the effect caffeine has on blood flow
to the heart. It can thus be concluded that people with CAD or those
at a high risk for heart disease should avoid loading up on caffeine
before a run or at least check with their primary care physician first.
Nutritional Supplements for Endurance Athletes 387
A final note in regard to caffeine supplementation is that the
International Olympic Committee lists caffeine as a banned substance.
Although some amount of caffeine is allowed because of its occur-
rence in foods, a urinary level that exceeds 12 mg/ml results in a doping
violation and possible disqualification or suspension. Therefore, it is
recommended to keep the daily caffeine intake to less than 3 mg/kg
body weight (i.e., 50–200 mg of caffeine) (44). Table 4 lists typical
caffeine content in common beverages, pills, and other products.
Although ephedrine is typically thought of as a weight loss sup-
plement, evidence supports its role in enhancing endurance exercise
performance. Ephedrine is a general sympathomimetic agent, which
means that it stimulates the CNS by mimicking the effects of many
of the body’s own sympathetic hormones [e.g., epinephrine (adrena-
line), norepinephrine] (50).
Ephedrine is found in various antiasthmatic and cold or cough
medications in pill, tablet, or inhaler form. It is also found in herbal
teas and dietary supplements containing Ma Huang (Chinese ephedra
or herbal ephedrine) as well as in dietary supplements marketed for
weight loss and for increasing energy. All cold medications with
decongestants are likely to contain prohibited sympathomimetics.
Typical doses used in research range from 20 to 25 mg ephedrine (42).
Table 4
Typical Caffeine Content in Common Beverages, Pills, and Other Products
Brewed coffee (cup)
a
= 100 mg
Decaffeinated coffee (cup) = 3 mg
Medium-brewed tea (cup) = 50 mg
Cocoa (cup) = 5 mg
Starbucks’ Coffee Grande (cup) = 90
Excedrin (one tablet) = 65 mg
No Doz (one tablet) = 100 mg
Vivarin (one tablet) = 200 mg
Guarana (100 mg) = 100 mg
SoBe No Fear (16 oz) = 159 mg
Cola-type soda (can) = 40 mg
Adapted from M.H. Williams (42), with permission
a
cup = 5–6 ounces
388 Rasmussen
Ephedrine is commonly combined with caffeine when assessing
its ergogenic potential. One study examined ephedrine and caffeine
separately and in combination in 12 subjects running a 10-km race.
The run times for the ephedrine-containing trials were significantly
shorter than those in the caffeine-only and placebo trials. In addi-
tion, heart rate and pace for the ephedrine-containing trials were
significantly lower than in the caffeine-only and placebo trials (58).
Another study examined the effects of caffeine and ephedrine on
running times of nine male subjects performing the Canadian Forces
Warrior Tests (WT). This is a standard test that all land forces soldiers
must perform within 22 minutes. Time to exhaustion was significantly
improved in the treatment group versus the placebo (1). The caffeine
and ephedrine enabled the subjects to exercise at a higher percentage
of the maximum aerobic power for a longer period of time when
compared with the placebo trials. These observations suggest that the
improved performance may have been due to the CNS stimulatory
effects of both caffeine and ephedrine (44). Ephedrine has a track
record of safe use at the recommended amount. Abuse of ephedrine,
however, can lead to amphetamine-like side effects, including elevated
blood pressure, rapid heart beat, nervousness, irritability, headache,
urination disturbances, vomiting, muscle disturbances, insomnia, dry
mouth, heart palpitations, and even death caused by heart failure
(59). It is important to note that ephedra use is banned by most
sports governing bodies (e.g., International Olympic Committee).
Additional research on the safety and efficacy of caffeine and ephe-
drine alone and in combination is warranted.
Physiological sports ergogenics are substances or techniques
designed specifically to augment natural physiological processes
that generate physical power. Two popular examples are glycerol
and creatine. Physiological sports ergogenics are not drugs per se. In
a strict sense, however, some may be regarded as drugs because they
are prescribed substances.
Glycerol is also known as glycerin and is an alcohol compound
that is more commonly found in the diet as a component of fat or
triglycerides. It serves as a backbone onto which fatty acid molecules
are attached and is marketed as an aid for ‘‘hyperhydrating’’ the body
by increasing blood volume and helping to delay dehydration. Thus,
glycerol may aid endurance athletes training or competing in hot,
humid environments by hydrating tissues, increasing blood volume,
Nutritional Supplements for Endurance Athletes 389
and ultimately delaying fatigue and exhaustion associated with dehy-
dration. Glycerin dosages used in research are based on body weight
or total body water and have approximated 1 g/kg body weight, with
each gram diluted in about 20 to 25mL of water or similar fluid (42).
Numerous studies support the theory that glycerol added to
fluids increase tissue hydration compared with drinking fluid with-
out glycerol added. Following glycerol consumption, the heart rate
and body core temperature are lower during exercise in the heat
(60), suggesting an ergogenic effect. In endurance type of activities a
larger supply of stored water may lead to a delay in dehydration and
exhaustion (61). More specifically, one study examined the effect of
glycerol (1 g/kg) supplementation on body temperature while exer-
cising on a treadmill (60% VO
2
max) at 428C at 25% relative humid-
ity for 90 minutes 2.5 hours after ingestion of the glycerol. Results
showed that the urine volume decreased before exercise, the sweat
rate increased, and the rectal temperature was lower during exercise
(62). These findings imply that glycerol ingestion was helpful in
maintaining normal body temperature during exercise in the heat.
Another study reporting positive results gave 11 fit adults gly-
cerol (1.2 g/kg in a 26 ml/kg body weight solution) or a placebo
(26 mg/kg body weight aspartame-flavored solution) 1 hour prior
to cycle exercise to exhaustion at 60% of maximum workload
(temperature 23.58–24.58C, humidity 25%–27%). The heart rate
for those taking glycerol was 2.8 bpm lower, and endurance time
was 21% longer (63). In a follow-up study, these same researchers
wanted to determine whether the same preexercise routine followed
by a carbohydrate oral replacement solution during exercise had any
further effect. Once again, they found that when glycerol had been
taken the endurance time was 25% longer (63).
It is important to note that not all studies show an ergogenic
effect and that the benefits—although noted for trained endurance
athletes exercising in hot, humid environments—are not necessarily
observed in athletes who are less well trained or are exercising in
more temperate climates (61,64). These factors should be taken into
account when considering glycerol supplements.
Although creatine supplements are typically marketed as body-
building and ‘‘strength-boosting’’ supplements, growing evidence
suggests that they may prove beneficial for endurance athletes as
well. Normally, about 1 to 2 g of creatine daily are produced in the
390 Rasmussen
body from the amino acids arginine, glycine, and methionine. Diet-
ary sources (Table 5), including meat and fish, add another 1 to 2 g
of creatine per day, although overcooking destroys most of the
creatine (the 1 g of creatine in an 8-oz steak may fall to zero if that
steak is well done).
In the body, creatine plays a vital role in cellular energy produc-
tion as creatine phosphate (phosphocreatine) in regenerating ATP
in skeletal muscle (50). Most studies utilize doses approximating 20
to 30 g/day, consumed in four or five equal doses throughout the day
for 5 to 7 days followed by a maintenance dose of 5 g/day (42).
One of the earliest creatine studies utilized well trained distance
runners and demonstrated improved cumulative, repeated running
times following four 300-m sprints (65). Another study demon-
strated significant increases in time to exhaustion during intense
cycle ergometry with creatine supplementation (66). Yet another
study reported that creatine loading in both male and female ath-
letes resulted in a 12% increase in the anaerobic threshold as well
as a decrease in blood lactate during incremental cycle tests (67).
One other study showed continued support by delaying the onset of
neuromuscular fatigue (a parameter similar to anaerobic threshold)
Table 5
Creatine Content in Select Foods
Food Creatine content
g/lb g/kg
Cod
Beef
Herring
Milk
Pork
Salmon
Shrimp
Tuna
Plaice
Fruits/vegetables
1.4
2.0
3.0–4.5
0.05
2.3
2.0
Trace
1.8
0.9
Trace
3.0
4.5
6.5–10.0
0.1
5.0
4.5
Trace
4.0
2.0
Trace
Adapted from Williams MH, Kreider RB, Branch D. Creatine:
The Power Supplement (p 15). Human Kinetics, Champaign,
IL, 1999
Nutritional Supplements for Endurance Athletes 391
by 13% in highly trained female athletes (68). Most scientists agree
that creatine’s effectivenss can be attributed to one of two scenarios:
1) Phosphocreatine may aid ATP resynthesis for up to 3 minutes,
albeit in a decreasing role with time and intensity of work (69);2)it
may act as an energy shuttle between the mitochondria and muscle
fibers, which suggests that creatine may help produce ATP aero-
bically (70). Regardless, increasing muscle creatine phosphate
levels through creatine supplementation may decrease the reliance
on anaerobic glycolysis and reduce intramuscular lactate accumula-
tion, thereby delaying the onset of fatigue (44). More research on
the effects of creatine supplementation on endurance performance is
needed before definitive conclusions can be drawn.
4. IMMUNE SYSTEM AND ENDURANCE
PERFORMANCE
Endurance athletes engaged in intense training run the risk of
overtraining. Overtraining is usually encountered after several days
of intense training and is generally associated with muscle fatigue.
During the training period, transient signs and symptoms may occur
including changes in the profile of mood state (POMS) where ten-
sion, depression, anger, fatigue, and confusion may be present.
Other signs include depleted muscle glycogen stores, increased rest-
ing heart rate, increased cortisol secretion, decreased appetite, sleep
disturbances, head colds, and immunosuppression. Most of the
symptoms that result from overtraining, collectively referred to as
overtraining syndrome, are subjective and identifiable only after the
individual’s performance has suffered. Unfortunately, these symp-
toms can be highly individualized, which can make it difficult for
athletes, trainers, and coaches to recognize that performance decre-
ments are brought on by overtraining. The first indication of over-
training syndrome is a decline in physical performance. The athlete
can sense a loss in muscle strength, coordination, and maximal
working capacity.
The immune system provides a line of defense against invading
bacteria, parasites, viruses, and tumor cells. The system depends on
the actions of specialized cells and antibodies. Unfortunately, one
of the most serious consequences of overtraining is the negative
effect it has on the body’s immune system. Recent studies confirm
392 Rasmussen
that excessive training suppresses normal immune function, increas-
ing the overtrained athlete’s susceptibility to infections (71,72).
Numerous studies show that short bouts of intense exercise can
temporarily impair the immune response, and successive days of
heavy training can amplify this suppression (73). Several investiga-
tors have reported an increased incidence of illness following a
single, exhaustive exercise bout. Also, intense exercise during illness
might decrease one’s ability to fight off infection and increases the
risk of even greater complications. In some cases, supplementation
may help attenuate the immunosuppression typically seen with
overtraining and in doing so may help prevent overtraining.
To bolster the first line of defense, an endurance athlete must
ensure that adequate calories are being consumed. Endurance ath-
letes maintaining heavy volume training often do not consume
enough calories to keep up with energy demands because of the
suppressive effect exercise can have on the appetite (74). This
point can be especially concerning for endurance athletes engaged
in prolonged training or competition sessions on the same or suc-
cessive days. Multiple training sessions on the same day have now
become the norm more than the exception for the elite endurance
athlete owing to the ever-increasing level of competition and pres-
sure to perform at optimal levels. An example is performing a long,
slow, distance (LSD) run in the morning only to follow-up with a
strength training session that evening. Although it is unlikely that
muscle glycogen stores can be completely resynthesized within a few
hours by nutritional supplementation alone, it would behoove all
endurance athletes to maximize the rate of muscle glycogen storage
after exercise. This ultimately results in faster recovery from train-
ing, possibly allowing a greater training volume (75).
To demonstrate the importance of nutrient timing, Flakoll et al.
(76) provided either a placebo, carbohydrate, or carbohydrate/
protein supplement to U.S. Marine recruits immediately after exer-
cise during 54 days of basic training to test the long-term impact of
postexercise carbohydrate/protein supplementation on variables
such as health, muscle soreness, and function. Compared to the
placebo and carbohydrate groups, the combined carbohydrate/pro-
tein group had 33% fewer total medical visits, 28% fewer visits due
to bacterial/viral infections, 37% fewer visits due to muscle and joint
problems, and 83% fewer due to heat exhaustion. Muscle soreness
Nutritional Supplements for Endurance Athletes 393
was also reduced immediately after exercise by the carbohydrate/
protein supplement. The authors postulated that post-exercise car-
bohydrate/protein supplementation not only may enhance muscle
protein deposition but also have significant potential to affect
health, muscle soreness, and tissue hydration positively during
prolonged intense exercise training. This suggests a potential ther-
apeutic approach for the prevention of health problems in severely
stressed exercising populations.
Hence, it is essential for the endurance athlete to consume an
adequate balance of macro and micronutrients at the proper times
throughout the day especially during periods of heavy training.
Athletes involved in intense training not only have greater macro-
nutrient needs but, more specifically, greater dietary protein needs
than individuals who do not train. Intense training has been shown
to decrease the availability of certain essential amino acids. Chronic
depletion of essential amino acids may slow the rate of tissue repair
and growth. Therefore, athletes involved in intense training need to
ingest enough high quality protein in the diet to maintain essential
amino acid availability during training. Dietary supplementation of
protein has been a common practice among athletes. More recently,
advances in food processing have allowed extraction of high quality
proteins from food. These proteins have been used in numerous
food products and have been marketed to athletes as a convenient
means of increasing the quality of protein in their diet.
Several ergogenic aids have been reported to aid the immune
system. Colostrum is the clear or cloudy ‘‘premilk’’ that female
mammals secrete after giving birth and before producing milk.
Colostrum for dietary supplements is usually derived from bovine
sources and contains various immunoglobulins (also called antibo-
dies) and antimicrobial factors (i.e., lactoferrin, lactoperoxidase, lyso-
zyme) as well as insulin-like growth factors (e.g., IGF-I, IGF-II).
Bovine colostrum is among the highest quality sources of protein.
The most prevalent claims for dietary supplements containing
colostrum are in the area of generalized immune function and
improved recovery from intense exercise. One study examined the
effects of consuming colostrum (60 g/day) or placebo (whey protein)
during an 8-week running program, running three times a week for
45 minutes per session (77). Participants conducted two treadmill
runs to exhaustion, with 20 minutes of rest between runs, at baseline
394 Rasmussen
and 4 and 8 weeks into the study. No differences existed in treadmill
running performance at baseline, and at week four both groups had
similar improvements in running performance. At week 8, however,
the colostrum group ran significantly farther and did more work
than the placebo group during the treadmill test. In addition, the
colostrum supplemented group exhibited lower serum creatine
kinase (CK) levels. CK is an important muscle cell enzyme that
some scientists believe can be used as a marker of muscle cell
damage. High CK levels often indicate that significant muscle
damage has occurred. However, some scientists believe that if CK
levels remain fairly normal, the athlete has experienced little muscle
trauma (77).
Another study examined rowing performance in a group of elite
female rowers. Eight rowers completed a 9-week training program
while consuming either colostrum (60 g/day) or whey protein. By
week 9, rowers consuming colostrum had greater increases in the
distance covered and work done than the whey protein group (78).
Additional studies on bovine colostrum consumption suggest that it
can deliver some generalized anti-inflammatory benefits (79,80)
and help prevent and treat the gastric injury associated with non-
steroidal anti-inflammatory drugs (81).
Glutamine is another supplement popular in athletic popula-
tions today. It is the most abundant amino acid in the body,
comprising approximately half of the free amino acids in the
blood and muscle. Glutamine is a nonessential glucogenic amino
acid and an anaplerotic precursor that has been shown to be a vital
fuel for a variety of cells of the immune system (82). In skeletal
muscle, glutamine has an inhibitory role on proteolysis and
branched-chain amino acid catabolism. Recent evidence has placed
emphasis on glutamine as a positive component of immune func-
tion (82,83).
Glutamine has two main functions in the body: It is a precursor in
the synthesis of other amino acids, and it converts to glucose for
energy. Cells of the immune system, small intestine, and kidney are
the major consumers of glutamine, making ‘‘immune boosting’’ and
‘immune maintenance’’ claims for glutamine supplements quite
common. In addition, there are claims for glutamine supplements
in maintaining muscle mass, reducing post-exercise catabolism
(muscle tissue breakdown), and accelerating recovery from intense
Nutritional Supplements for Endurance Athletes 395
exercise. Intense exercise training often exhibited by the endurance
athlete results in a drop in plasma glutamine levels. Chronically low
glutamine levels have been implicated as a possible contributing
factor for athletic overtraining syndrome as well as the transient
immunosuppression and increased risk of infections that typically
affect competitive athletes during intense training and competition.
Under conditions of metabolic stress, the body’s need for glutamine
may become conditionally essential, meaning that the body cannot
produce adequate levels and a dietary source is required to prevent
catabolism of skeletal muscle, the primary source of stored gluta-
mine in the body.
A significant body of scientific literature supports the beneficial
effects of glutamine supplementation in maintaining muscle mass
and immune system function in critically ill patients and in those
recovering from extensive burns and major surgery (84). When
plasma glutamine levels fall, skeletal muscles may enter a state of
catabolism in which muscle protein is degraded to provide free
glutamine for the rest of the body. Because skeletal muscle is the
major source of glutamine (other than the diet), prolonged deficits
in plasma glutamine can lead to a significant loss of skeletal muscle
protein and muscle mass. Postsurgical deposition of collagen (a
marker for wound healing) can be enhanced by amino acid sup-
plementation containing 14 g of glutamine (85), whereas a lower
dose of mixed amino acids containing glutamine (2.9 g) provides
no change in athletic performance or on adaptations to cycling
training (86).
Studies have also been conducted on glutamine supplementation
in athletes, and a strong rationale exists for the efficacy of glutamine
supplements in athletic populations. One study found that athletes
who consumed glutamine immediately and 2 hours after running a
marathon or ultramarathon reported fewer infections than a pla-
cebo group (87). The levels of infection were lowest in the middle
distance runners and highest in the runners after a marathon or
ultramarathon. Glutamine supplements have also been shown to
play a role in counteracting the catabolic effects of stress hormones,
such as cortisol, which are typically elevated by strenuous exercise.
Under conditions of stress-induced protein wasting in adults and
children, including burns, surgery, and some forms of cancer, glu-
tamine supplementation has been associated with reduced protein
396 Rasmussen
breakdown (88), enhanced lymphocyte function (89), reduced gut
permeability (90), and reduced infections (91).
In addition to lowering glutamine levels, prolonged strenuous
exercise has been reported to lower zinc levels apparently owing to
greater zinc loss during training from sweat and/or inadequate
intake of dietary zinc (92). Zinc deficiency has been reported to
diminish serum testosterone levels (93), impair immune function
(94), and decrease strength (95). Zinc is an essential trace mineral
that functions as part of about 300 enzymes. As such, zinc plays a
role in numerous biochemical pathways and physiological pro-
cesses. Because of the varied roles of zinc in the body, claims for
zinc-containing dietary supplements are numerous, including those
for improved wound healing, general immune system support, and
support of various aspects of men’s health.
Zinc lozenges have become one of the most popular natural
approaches to treating the common cold. The scientific evidence
generally supports this use for short periods (1–2 weeks) (96). Zinc
lozenges appear to reduce cold symptoms, such as sore throats,
hoarseness, and coughing, and may even be able to shorten the
duration of colds by a full day.
Exercise performance has been associated with decreased zinc
status, especially in athletes who avoid red meat, who concentrate
their diets too much on carbohydrates, or who follow an overly
restricted dietary regimen. Low zinc intake (<3 mg/day) has been
linked to reduced activity of a zinc-containing enzyme in red blood
cells, carbonic anhydrase, which helps red blood cells transport
carbon dioxide from tissues to the lungs to be exhaled. Mild-to-
moderate zinc deficiency can lead to significant reductions in the
body’s ability to take up and use oxygen, remove carbon dioxide,
and generate energy during high-intensity exercise (50).
One study examined the effects of daily physical training on
serum and sweat zinc concentrations in professional sportsmen
between October and December, during the competition season.
They discovered a significantly higher zinc concentration in sweat
in December than in October. They stated that a daily and main-
tained exercise routine was probably responsible for the altered zinc
metabolism. The authors further concluded that alterations in zinc
metabolism with increases in zinc excretion and stress levels lead to a
situation of latent fatigue associated with decreased endurance (97).
Nutritional Supplements for Endurance Athletes 397
Another study attempted to investigate how exhaustive exercise
affects thyroid hormones and testosterone levels in male wrestlers
who were supplemented with oral zinc sulfate (3 mg/kg/day) for
4 weeks. The results demonstrated that exhaustive exercise led to
significant inhibition of both thyroid hormones and testosterone
concentrations but that 4-week zinc supplementation prevented this
inhibition in wrestlers. The authors concluded that physiological
doses of zinc administration may benefit performance (98). Another
study, however, examined plasma zinc concentrations and markers
of immune function in 10male runners following a moderate increase
in training over 4weeks and found no benefit in zinc concentration,
differential leukocyte counts, lymphocyte subpopulations, or lym-
phocyte proliferation. These authors concluded that athletes are
unlikely to benefit from zinc supplementation during periods of
moderately increased training volume (99).
Overall, then, studies on colostrum, glutamine, and zinc have
provided favorable evidence that they support the immune system
and should be considered by the endurance athlete engaged in
intense training.
5. ADDITIONAL CONCERNS
Despite the fact that there is solid scientific evidence backing the
safety and efficacy of certain nutritional supplements, some remain
skeptical as to whether they should be used at all. The two most
popular questions raised generally address legal and ethical consid-
erations. Although some drugs may be effective sports ergogenics,
their use might also significantly increase health risks. The Medical
Commission of the International Olympic Committee (IOC) noted
that doping violates the ethics of both sport and medical science and
is prohibited. Most athletic governing bodies, such as the IOC, the
National Basketball Association (NBA), the National Football
League (NFL), The National Collegiate Athletic Association
(NCAA), and the United States Olympic Committee (USOC) have
developed drug-use policies. Any athlete competing under the jur-
isdiction of a specific athletic governing body should be aware of its
drug rules and regulations before consuming any nutritional supple-
ment designed to aid performance.
398 Rasmussen
What are the ethics of sport? According to Webster’s Dictionary,
the definition for ethics includes the following: 1) the discipline
dealing with what is good and bad and with moral duty and obliga-
tion; 2) a theory or system of moral values; 3) the principles of
conduct governing an individual or group; and 4) a guiding philo-
sophy. All four definitions can be operational in sports.
The IOC embraces the idea that athletes should succeed through
their unaided efforts; in other words, the ‘‘Do the best with what
you’ve got’’ approach. However, the athlete whose primary goal is
to win at all costs may be guided by his or her own principles in an
attempt to obtain that unfair advantage. With increasing pressures
to perform and potential scholarships, jobs, endorsements, and
contract extensions on the line, an increasing number of elite ath-
letes participating in both the collegiate and professional ranks are
learning to modify their natural ability by techniques that go beyond
normal training in order to get an advantage—not necessarily an
unfair one—over their competitors. As noted throughout this chap-
ter, safe, effective, legal ergogenics are available. Whether their use is
ethical may depend on the individual athlete’s code of ethics. Some
authorities believe that because a sports ergogenic is legal, its use is
ethical. Others may contend that such a sports ergogenic violates the
ethics of the IOC antidoping rule. In this situation, the ultimate
decision about whether to use a safe, effective, legal ergogenic rests
with the individual athlete.
6. CONCLUSION
Proper training, maintaining a positive energy balance, and uti-
lizing effective nutritional supplements form the foundation for
optimal performance. Training for the endurance athlete should be
based on proper utilization of the principles of training, depending
on individual goals and the training season (preseason, in-season,
postseason). The nutritional base should focus on an everyday diet
that emphasizes a combination of all the nutritional ergogenic aids.
The types of macronutrients and micronutrients selected and the
timing of their use are of the utmost importance for developing a
well refined everyday diet. The use of nutritional supplements that
research has shown can help improve energy availability (e.g., sports
Nutritional Supplements for Endurance Athletes 399
drinks, carbohydrate) and/or promote recovery (e.g., carbohydrate,
protein) can provide additional benefits in certain situations. In
addition, a combination of effective pharmacological and physiolo-
gical ergogenic supplements can further propel performance and
support the immune system. Following these training and nutri-
tional recommendations can serve as the foundation for a successful
endurance athlete.
7. PRACTICAL APPLICATIONS
To prepare for competition, endurance athletes should strive to hyper-
hydrate prior to exercise. Full hydration requires that water along with
fluids containing moderate concentrations of carbohydrate and sodium
be ingested regularly starting several days before competition.
Endurance athletes should try to maximize their muscle glycogen stores
prior to competition. This can be accomplished during the training taper
by consuming 7 to 10 g carbohydrates/kg body weight daily.
Prior to competition, it is recommended that 500 to 1000 ml of fluid be
ingested. It may also be beneficial to consume 200 to 300 g of carbohy-
drate if supplementation during exercise is limited or not possible.
During exercise, endurance athletes should try to replace fully any fluid
losses that occur, although during hot and humid conditions this may be
next to impossible.
It is best to consume small volumes of fluid frequently (150–250 ml every
15 minutes) rather than consume high volumes of fluid occasionally
(e.g., 400 ml every 30 minutes).
Electrolyte replacement should be considered by the endurance athlete.
Most sports drinks are formulated adequately to replace electrolyte
losses due to sweating.
To maximize endurance performance, 45 to 60 g of high glycemic index
(GI) carbohydrates should be ingested per hour during exercise. Carbo-
hydrate solutions should not exceed 10% if maintaining hydration is of
importance.
Carbohydrate supplementation can be delayed until about 30 to 40 min-
utes prior to the onset of fatigue and still be effective. However, if fluid
replacement is of concern, it is recommended that supplementation with
a dilute carbohydrate solution start as soon as possible and continued
periodically throughout exercise.
The addition of small amounts of protein to a carbohydrate supplement
(4:1 ratio) may also increase the effectiveness of the supplement.
400 Rasmussen
For rapid rehydration following exercise, it is important to start fluid
consumption early and replace at least 150% of the fluid lost during
exercise with a dilute sodium solution.
Requirements for the daily recovery of muscle glycogen depend on exer-
cise intensity and duration. If the training duration is moderate and the
intensity is low, 5 to 7 g of carbohydrate (CHO)/kg/day should be con-
sumed. If the training duration is moderate and the intensity is high, 7 to
12 g CHO/kg/day should be consumed. If the training is extreme
(4–6 hours per day), 10 to 12 g CHO/kg/day should be consumed.
If there is only limited time to replenish the muscle glycogen stores, 1.0
to 1.2 g CHO/kg/hr should be consumed at frequent intervals starting
within the first 30 minutes after exercise.
The addition of protein to the carbohydrate supplement (4:1 ratio)
promotes additional glycogen storage when carbohydrate intake is
suboptimal or when frequent supplementation is not possible.
Post-exercise supplements composed of carbohydrate and protein have
the added benefit of limiting muscle tissue damage, stimulating protein
accretion, and protecting the immune system from exercise-induced
immunosuppression.
Several pharmacological and physiological ergogenic aids can further
propel performance for the endurance athlete and should be considered
depending on the individual goal of the athlete.
There is strong evidence that colostrum, glutamine, and zinc support the
immune system. Hence, these supplements should be considered by the
endurance athlete engaged in intense training.
REFERENCES
1. Bell DG, Jacobs I. Combined caffeine and ephedrine ingestion improves
run times of Canadian Forces Warrior Test. Aviat Space Environ Med
1999;70:325–328.
2. Blomstrand E, Hassem P, Ekblom B, Newsholme EA. Administration of
branched-chain amino acids during sustained exercise-effects on performance
and plasma concentration of some amino acids. Eur J Appl Physiol
1991;63:83–88.
3. Bridge CA, Jones MA. The effect of caffeine ingestion on 8 km run perfor-
mance in a field setting. J Sports Sci 2006;24:433–439.
4. Erickson MA. Effects of caffeine, fructose, and glucose ingestion on muscle
glycogen utilization during exercise. Med Sci Sports Exerc 1987;19:579–583.
5. Kreider RB, Miller GW, Williams MH, Somma CT, Nasser TA. Effects of
phosphate loading on oxygen uptake, ventilatory anaerobic threshold, and
run performance. Med Sci Sports Exerc 1990;22:250–256.
Nutritional Supplements for Endurance Athletes 401
6. Mittleman KD, Ricci MR, Bailey SP. Branched-chain amino acids prolong
exercise during heat stress in men and women. Med Sci Sports Exerc
1998;30:83–91.
7. Saunders MJ, Kane MD, Todd MK. Effects of a carbohydrate-protein beverage
on cycling endurance and muscle damage. Med Sci Sports Exerc
2004;36:1233–1238.
8. Coyle EF, Montain SJ. Benefits of fluid replacement with carbohydrate
during exercise. Med Sci Sports Exerc 1992;24:S324–S330.
9. Armstrong LE, Costill DL, Fink WJ. Influence of diuretic-induced dehydration
on competitive running performance. Med Sci Sports Exerc 1985;17:456–461.
10. Sutton JR, Bar-Or O. Thermal illness in fun running. Am Heart J
1980;100:778–781.
11. Coyle EF. Substrate utilization during exercise in active people. Am J Clin
Nutr 1995;61(Suppl):968S–979S.
12. Thibault G. Ahead of the pack. Training Cond 2006;16:25–31.
13. Kreider R, Fry AC, O’Toole ML (eds). Overtraining in Sport. Human
Kinetics, Champaign, IL, 1998.
14. Carli G. Changes in the exercise-induced hormone response to branched
chain amino acid administration. Eur J Physiol Occup Physiol
1992;64:272–277.
15. Cade JR. Dietary intervention and training in swimmers. Eur J Physiol Occup
Physiol 1997;63:210–215.
16. Kreider RB. Dietary supplements and the promotion of muscle growth with
resistance exercise. Sports Med 1999;27:97–110.
17. Komi PV (ed). Strength and Power in Sport. Blackwell Scientific, Cambridge,
MA, 1992.
18. Brand-Miller J, Wolever TMS, Colagiuri S, Foster-Powell K (eds). The
Glucose Revolution. Marlowe, New York, 1999.
19. Coyle EF, Montain SJ. Carbohydrate and fluid ingestion during exercise: are
there trade-offs? Med Sci Sports Ex 1992;24:671–678.
20. Noakes TD, Myburgh KH, Du Plessia J, et al. Metabolic rate, not percent
dehydration, predicts rectal temperature in marathon runners. Med Sci
Sports Exerc 1991;23:443–449.
21. Bergstrom J, Hermansen L, Hultman E, Saltin B. Diet, muscle glycogen and
physical performance. Acta Physiol Scand 1967;71:140–150.
22. Balsom PD, Gaitanos GC, Soderlund K, Ekblom B. High-intensity exercise
and muscle glycogen availability in humans. Acta Physiol Scand
1999;165:337–345.
23. Volek JS. Influence of nutrition on responses to resistance training. Med Sci
Sports Exerc 2004;36:689–696.
24. Ivy JL, Res PT, Sprague RC, Widzer MO. Effect of a carbohydrate-protein
supplement on endurance performance during exercise of varying intensity.
Int J Sport Nutr Exerc Metab 2003;13:382–395.
25. Anderson LL, Tufekovic G, Zebis MK, et al. The effect of resistance training
combined with timed ingestion of protein on muscle fiber size and muscle
strength. Metabolism 2005;54:151–156.
402 Rasmussen
26. Dangin M, Boirie Y, Garcia-Rodenas C, et al. The digestion rate of protein is
an independent regulating factor of postprandial protein retention. Am J
Physiol Endocrinol Metab 2001;280:E340–E348.
27. Ivy JL, Portman R (eds) The Performance Zone. Basic Health Publications,
North Bergen, NJ, 2004.
28. Costill D, Hargreaves M. Carbohydrate nutrition and fatigue. Sports Med
1992;13:86–92.
29. Ivy JL. Muscle glycogen synthesis before and after exercise. Sports Med
1991;11:6–11.
30. Houston M (ed). Biochemistry Primer for Exercise Science. Human Kinetics,
Champaign, IL, 1995.
31. Ivy JL. Glycogen resynthesis after exercise: effect of carbohydrate intake. Int J
Sports Med 1998;19:S142–S145.
32. Haymond M. Hypoglycemia in infants and children. Endocrinol Metab Clin
North Am 1989;18:211–252.
33. Gastelu D, Hatfield F (eds). Nutrition for Maximum Performance. Avery,
Garden City Park, NY, 1997.
34. Blom P, Hostmark A, Vaage O, Kardel K, Maehlum S. Effects of different
post-exercise sugar diets on the rate of muscle glycogen synthesis. Med Sci
Sports Exerc 1987;19:491–496.
35. Burke L, Collier G, Hargreaves M. Muscle glycogen storage after prolonged
exercise: effect of the glycemic index of carbohydrate feedings. J Appl Physiol
1993;75:1019–1023.
36. Jentjens RLPG, van Loon LJC, Mann CH, Wagenmakers AJM, Jeukendrup
AE. Addition of protein and amino acids to carbohydrates does not enhance
post-exercise muscle glycogen synthesis. J Appl Physiol 2001;91:839–846.
37. Tarnopolsky MA, Bosman M, Macdonald JR, Vandeputte D, Martin J, Roy
BD. Post-exercise protein-carbohydrate and carbohydrate supplements
increase muscle glycogen in men and women. J Appl Physiol
1997;83:1877–1883.
38. Evans WJ. Protein nutrition and resistance exercise. Can J Appl Physiol
2001;26(Suppl):S141–S152.
39. Ivy JL, Katz AL, Dutler CL, Sherman WM, Cyyle EF. Muscle glycogen
synthesis after exercise: effect of time of carbohydrate ingestion. J Appl
Physiol 1988;64:1480–1485.
40. Garetto OP, Richter EA, Goodman MN, Ruderman NB. Enhanced muscle
glucose metabolism after exercise in the rat: the two phases. Am J Physiol
1984;246:E471–E475.
41. Miller SL, Tipton KD, Chinkes DL. Independent and combined effects of
amino acids and glucose after resistance exercise. Med Sci Sports Exerc
2003;35:449–455.
42. Williams MH. The Ergogenics Edge. 1st ed. Human Kinetics, Champaign, IL,
1998.
43. Cade R, Conte M. Effects of phosphate loading on 2,3-diphosphoglycerate
and maximum oxygen uptake. Med Sci Sports Exerc 1984;16:263–268.
Nutritional Supplements for Endurance Athletes 403
44. Antonio J, Stout J. Supplements for Endurance Athletes. Human Kinetics,
Champaign, IL, 2002.
45. Blomstrand E, Celsing F, Newsholme EA. Changes in plasma concentrations
of aromatic and branched-chain amino acids during sustained exercise in man
and their possible role in fatigue. Acta Physiol Scand 1988;1:115–121.
46. Castell LM, Yamamoto T, Phoenix J, Newsholme EA. The role of tryptophan
in fatigue in different conditions of stress. Adv Exp Med Biol
1999;467:697–704.
47. Davis JM. Carbohydrates, branched-chain amino acids, and endurance: the
central fatigue hypothesis. Int J Sport Nutr 1995;5(Suppl):S29–S38.
48. Hassmen P, Blomstrand E, Ekblom B, Newsholme EA. Branched-chain
amino acid supplementation during 30-km competitive run: mood and cog-
nitive performance. Nutrition 1994;10:405–410.
49. Tanaka H, West KA, Duncan GE, Bassett DRJ. Changes in plasma trypto-
phan/branched chain amino acid ration in responses to training volume
variation. Int J Sport Nutr 1997;18:270–275.
50. Talbott SM, Hughes K. The Health Professional’s Guide to Dietary Supple-
ments. 1st ed. Lippincott Williams & Wilkins, Philadelphia, 2007.
51. Gastmann UA, Lehmann MJ. Overtraining and the BCAA hypothesis. Med
Sci Sports Exerc 1998;30:1173–1178.
52. Van Hall G, Raaymakers JS, Saris WH, Wagenmakers AJ. Ingestion of
branched-chain amino acids and tryptophan during sustained exercise in
man: failure to affect performance. J Physiol 1995;486:789–794.
53. Davis JM, Bailey SP, Woods JA, Galiano FJ, Hamilton MT, Bartoli WP.
Effects of carbohydrate feedings on plasma free tryptophan and branched-
chain amino acids during prolonged cycling. Eur J Appl Physiol Occup
Physiol 1992;65:513–519.
54. Costill DL, Dalsky GP, Fink WJ. Effects of caffeine ingestion on metabolism
and exercise performance. Med Sci Sports Exerc 1978;10:155–158.
55. Spreit LL, MaClean DA, Dyck DJ, Hultmant E. Caffeine ingestions and
muscle metabolism during prolonged exercise in humans. Am J Physiol
1992;262:E891–E898.
56. Schneiker KT, Bishop D, Dawson B, Hackett LP. Effects of caffeine on
prolonged intermittent-sprint ability in team-sport athletes. Med Sci Sports
Exerc 2006;38:578–585.
57. Namdar M, Koepfli P, Grathwohl R, et al. Caffeine decreases exercise-
induced myocardial flow reserve. J Am Coll Cardiol 2006;47:405–410.
58. Bell DG, McLennan TM, Sabiston CM. Effect of ingesting caffeine and
ephedrine on 10-km run performance. Med Sci Sports Exerc 2002;34:344–349.
59. Blumenthal M, Busse WR, Goldberg A (eds). The Complete Commission E
Monographs: Therapeutic Guide to Herbal Medicines. Integrative Medicine
Communications, Boston, 1998.
60. Jimenez C, Melin B, Doulmann N, Allevard AM, Launay JC, Savourey G.
Plasma volume changes during and after acute variations of body hydration
level in humans. Eur J Appl Physiol Occup Physiol 1999;80:1–8.
404 Rasmussen
61. Wagner DR. Hyperhydrating with glycerol: implications for athletic perfor-
mance. J Am Diet Assoc 1999;99:207–212.
62. Lyons TP, Riedesel ML, Meuli LE, Chick TW. Effects of glycerol-induced
hyperhydration prior to exercise in the heat on sweating and core tempera-
ture. Med Sci Sports Exerc 1990;22:477–483.
63. Montner P, Stark DM, Riedesel ML. Pre-exercise glycerol hydration
improves cycling endurance time. Int J Sports Med 1996;17:27–33.
64. Arnall DA, Goforth HWJ. Failure to reduce body water loss in cold-water
immersion by glycerol ingestion. Undersea Hyperb Med 1993;20:309–320.
65. Harris RC, Viru M, Greenhaff PL, Hultman E. The effect of oral creatine
supplementation on running performance during maximal short term exercise
in man. J Physiol 1993;467:74P.
66. Smith JC, Stephens DP, Hall EL, Jackson AW, Earnest CP. Effect of oral
creatine ingestion on parameters of the work rate-time relationship and time
to exhaustion in high-intensity cycling. Eur J Appl Physiol 1998;77:360–365.
67. Nelson A, Day R, Glickman-Weiss E, Hegstad M, Sampson B. Creatine
supplementation alters the response to a graded cycle ergometer test. Eur J
Appl Physiol 2000;83:89–94.
68. Stout J, Eckerson J, Ebersole K, et al. Effect of creatine loading on neuro-
muscular fatigue threshold. J Appl Physiol 2000;88:109–112.
69. Bangsbo J, Gollnick PD, Graham TE. Anaerobic energy production and O
2
deficit-debt relationship during exhaustive exercise in humans. J Physiol
1990;422:539–559.
70. Wallimann T, Wyss M, Brdiczka D, Nicolay K, Eppenberger HM. Intracel-
lular compartmentation, structure and function of creatine kinase isoenzymes
in tissues with high and fluctuating energy demands: the ‘phosphocreatine
circuit’ for cellular energy homeostasis. Biochem J 1992;281:21–40.
71. Mackinnon LT. Exercise and natural killer cells: what is the relationship?
Sports Med 1989;7:141–149.
72. McCarthy DA, Dale MM. The leucocytosis of exercise: a review and model.
Sports Med 1988;6:333–363.
73. Brahmi Z, Thomas JE, Park M, Dowdeswell IRG. The effect of acute exercise
on natural killer cell activity of trained and sedentary subjects. J Clin Immu-
nol 1985;5:321.
74. Berning JR. Energy intake, diet and muscle wasting. In: Kreider RB, Fry AC,
O’Toole ML (eds) Overtraining in Sport (pp 275–288). Human Kinetics,
Champaign, IL, 1998.
75. Haff GG, Lehmkuhl MJ, McCoy LB, Stone MH. Carbohydrate supplemen-
tation and resistance training. J Strength Cond Res 2003;7:187–196.
76. Flakoll PJ, Judy T, Flinn K, Carr C, Flinn S. Postexercise protein supple-
mentation improves health and muscle soreness during basic military training
in marine recruits. J Appl Physiol 2001;96:951–956.
77. Buckley J. Effect of oral bovine colostrum supplement (Intact) on running
performance. In: Proceedings of the Australian Conference of Science and
Medicine in Sport (p 79).
Nutritional Supplements for Endurance Athletes 405
78. Brinkworth GD, Buckley JD, Bourdon PC, Gulbin JP, David A. Oral bovine
colostrum supplementation enhances buffer capacity but not rowing perfor-
mance in elite female rowers. Int J Sport Nutr Exerc Metab 2002;12:349–365.
79. Bolke E, Jehle PM, Hausmann F, et al. Preoperative oral application of
immunoglobulin-enriched colostrum milk and mediator response during
abdominal surgery. Shock 2002;17:9–12.
80. Playford RJ, MacDonald CE, Calnan DP, et al. Co-administration of the
health food supplement, bovine colostrum, reduces the acute non-steroidal
anti-inflammatory drug-induced increase in intestinal permeability. Clin Sci
(Lond) 2001;100:627–633.
81. Khan Z, Macdonald C, Wicks AC, et al. Use of the ‘nutriceutical,’’ bovine
colostrum, for the treatment of distal colitis: results from an initial study.
Aliment Pharmacol Ther 2002;16:1917–1922.
82. Ardawi MSM, Newsholme EA. Glutamine metabolism in lymphocytes of
rats. Biochem J 1983;212:835.
83. Ardawi MSM, Newsholme EA. Metabolism in lymphocytes and its impor-
tance in immune response. Essays Biochem 1985;21:1.
84. Carli F, Webster J, Ramachandra V, et al. Aspects of protein metabolism
after elective surgery in patients receiving constant nutritional support. Clin
Sci (Colch) 1990;78:621–628.
85. Williams JZ, Abumrad N, Barbul A. Effect of a specialized amino acid
mixture on human collagen deposition. Ann Surg 2002;236:369–374.
86. Vukovich MD, Sharp RL, Kesl LD, Schaulis DL, King DS. Effects of a low-
dose amino acid supplement on adaptations to cycling training in untrained
individuals. Int J Sport Nutr 1997;7:298–309.
87. Castell LM, Poortmans JR, Newsholme EA. Does glutamine have a role in
reducing infections in athletes? Euro J Appl Physiol 1996;73:488–490.
88. Des Robert C, Le Bacquer O, Piloquet H, Roze JC, Darmaun D. Acute
effects of intravenous glutamine supplementation on protein metabolism
in very low birth weight infants: a stable isotope study. Pediatr Res
2002;51:87–93.
89. Yoshida S, Kaibara A, Ishibashi N, Shirouzu K. Glutamine supplementation
in cancer patients. Nutrition 2001;17:766–768.
90. Klimberg VS, Nwokedi E, Hutchins LF, et al. Glutamine facilitates che-
motherapy while reducing toxicity. JPEN J Parenter Enteral Nutr
1992;16:83S–87S.
91. Barbosa E, Moreira EA, Goes JE, Faintuch J. Pilot study with a glutamine-
supplemented enteral formula in critically ill infants. Rev Hosp Clin Fac Med
Sao Paulo 1999;54:21–24.
92. Khaled S, Brun JF, Micallef JP, et al. Serum zinc and blood rheology in
sportsmen (football players). Clin Hemorheol Microcirc 1997;17:47–58.
93. Om A, Chung K. Dietary zinc deficiency alters 5 alpha-reduction and aroma-
tization of testosterone and androgen estrogen receptors in rat liver. J Nutr
1996;126:842–848.
94. Nieman DC. Nutrition, exercise, and immune system function. Clin Sports
Med 1999;18:537–548.
406 Rasmussen
95. Van Loan MD, Sutherland B, Lowe NM, Turnland JR, King JC. The effects
of zinc depletion on peak force and total work of knee and shoulder extensor
and flexor muscles. Int J Sport Nutr 1999;9:125–135.
96. Eby GA. Zinc ion availability: the determinant of efficacy in zinc lozenge
treatment of common colds. J Antimicrob Chemother 1997;40:483–493.
97. Cordova A, Navas FJ. Effect of training on zinc metabolism: changes in
serum and sweat zinc concentrations in sportsmen. Ann Nutr Metab 1998;
42:274–282.
98. Kilic M, Baltaci AK, Gunay M, Gokbel H, Okudan N, Cicioglu I. The effect
of exhaustion exercise on thyroid hormones and testosterone levels of elite
athletes receiving oral zinc. Neuro Endocrinol Lett 2006;27:247–252.
99. Peake JM, Gerrard DF, Griffin JF. Plasma zinc and immune markers in
runners in response to a moderate increase in training volume. Int J Sports
Med 2003;24:212–216.
100. Gisolfi CV, Lamb DR (eds). Fluid Homeostasis During Exercise (Perspec-
tives in Exercise and Sports Medicine). Benchmark Press, Indianapolis, 1990.
Nutritional Supplements for Endurance Athletes 407
... Athletes who practice endurance disciplines such as running often use supplements that help improve their athletic performance (Rasmussen et al., 2008, Carlsohn et al., 2011. Supplements such as caffeine appear to have an effect on the performance of endurance athletes by stimulating the central nervous system and the release of epinephrine optimizing cardiovascular function. ...
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