Supplements for Endurance Athletes

Abstract

ENDURANCE ATHLETES EXPEND REMARKABLE AMOUNTS OF ENERGY AND CHALLENGE THE RECOVERY PROCESSES OF THEIR BODIES. SCORES OF NUTRITIONAL SUPPLEMENTS ARE MARKETED FOR THEIR ABILITY TO IMPROVE ONE OR BOTH OF THESE PROCESSES. A LIMITED NUMBER OF THESE SUPPLEMENTS HAVE AN APPRECIABLE AMOUNT OF RESEARCH TO SUPPORT THEIR USE BY ENDURANCE ATHLETES. CARBOHYDRATE-ELECTROLYTE SOLUTIONS, CAFFEINE, AND ADDING PROTEIN TO CARBOHYDRATE SUPPLEMENTATION OR MEALS ARE 3 STRATEGIES THAT ARE SCIENTIFICALLY BACKED AND SHOULD BE CONSIDERED AS A TRAINING AID FOR THOSE ENDURANCE ATHLETES WHO COMPETE AND TRAIN ON A REGULAR BASIS.

Full text

Supplements for
Endurance Athletes
Chad Kerksick, PhD, ATC, CSCS*D, NSCA-CPT*D
1,2,3
and Mike Roberts, MS, CSCS
1
1
Department of Health and Exercise Science, University of Oklahoma, Norman, Oklahoma;
2
Section of Endocrinology
and Diabetes, Department of Pediatrics, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma;
and
3
Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma
SUMMARY
ENDURANCE ATHLETES EXPEND
REMARKABLE AMOUNTS OF EN-
ERGY AND CHALLENGE THE RE-
COVERY PROCESSES OF THEIR
BODIES. SCORES OF NUTRI-
TIONAL SUPPLEMENTS ARE MAR-
KETED FOR THEIR ABILITY TO
IMPROVE ONE OR BOTH OF THESE
PROCESSES. A LIMITED NUMBER
OF THESE SUPPLEMENTS HAVE AN
APPRECIABLE AMOUNT OF RE-
SEARCH TO SUPPORT THEIR USE
BY ENDURANCE ATHLETES. CAR-
BOHYDRATE-ELECTROLYTE SOL-
UTIONS, CAFFEINE, AND ADDING
PROTEIN TO CARBOHYDRATE
SUPPLEMENTATION OR MEALS
ARE 3 STRATEGIES THAT ARE
SCIENTIFICALLY BACKED AND
SHOULD BE CONSIDERED AS A
TRAINING AID FOR THOSE EN-
DURANCE ATHLETES WHO COM-
PETE AND TRAIN ON A REGULAR
BASIS.
INTRODUCTION
Reports of athletes consuming
specific foods, nutrients, or in-
gredients to optimize perfor-
mance can be traced back for
centuries. Endurance athletes, by virtue
of training for their sporting compet-
itions, can expect to burn tens of
thousands of calories. It is estimated
that a typical male endurance athlete
will expend approximately 1,000 kcal
and a female 600–700 kcal when
completing an hour of activity at
approximately 70% of their maximal
oxygen uptake (i.e.,
_
VO
2
max) (59).
With this remarkable demand for
energy and a desire to adopt various
training or nutritional strategies to
maximize performance, the interest in
nutritional supplements to aid in this
process continues to be popular.
In a 2004 survey addressed to 207
collegiate athletes, many of who par-
ticipated in endurance-oriented sports,
only 11% of the respondents claimed
to have never consumed a nutritional
supplement (25). Their reasons for
supplementing included a desire to
increase health and energy levels and
decrease the chance for injury. Al-
though supplements that fulfill the
aforementioned claims do exist, there
are several supplements (albeit, indi-
vidual ingredients or proprietary
blends) which, to date, have not
proven to be beneficial for endurance
performance and/or recovery in labo-
ratory settings (Table 1). Therefore,
this review will attempt to discuss
those nutritional supplements that
have adequate scientific support for
their ability to impact endurance
training and performance. Although
other notable supplements have stud-
ies to support their consideration such
as medium-chain triglycerides, phos-
phates, carnitine, or glycerol supple-
mentation, the conclusions are
equivocal. Currently, the literature
surrounding carbohydrate-electrolyte
solutions (sports drinks), caffeine, and
ingestion of carbohydrate + protein
during exercise and after exercise to
facilitate performance and promote
recovery is widespread and continues
to grow in support.
CARBOHYDRATE-ELECTROLYTE
BEVERAGES
BACKGROUND
In a historical sense, reports surround-
ing the ingestion of sugary candy and
sweets before endurance events go
back the early 1900s. From there,
Swedish scientists in the 1960s re-
ported that high carbohydrate feedings
before and during exercise increased
endurance performance parameters
(43), and a few years later, the first
commercial carbohydrate-electrolyte
drink became available. Although much
of the attention for carbohydrate-
electrolyte beverages has centered on
increasing performance, carbohydrate-
electrolyte beverages can also atten-
uate fatigue, replace lost fluid and
carbohydrate, prevent extraneous los-
ses of important electrolytes, and
assist in thermoregulation during pro-
longed athletic events (15,59). It is
these combinations of effects that make
carbohydrate-electrolyte solutions one
of the most effective nutritional supple-
ments for an endurance athlete (56).
FLUID AND ELECTROLYTE
REPLACEMENT
Endurance athletes can have sweat
rates ranging from 1.2 to 1.7 liters of
bodily fluid (i.e., approximately 2%
bodyweight in a 70 kg athlete) per
hour (63), with the highest docu-
mented sweat rate being 4.2 liters per
KEY WORDS:
carbohydrate; caffeine; electrolyte;
glycogen; performance; sport; exercise;
recovery
Copyright ÓNational Strength and Conditioning Association Strength and Conditioning Journal | www.nsca-lift.org 55

hour (59). Considering that a serious
decrement in performance can occur
after only a 2% reduction in body mass
from fluid and this can occur after only
1 hour (Table 2), endurance athletes
need to take strides to ensure that
optimal fluid rehydration occurs (63).
In this respect, simply taking strides
to adequately replace fluids when
exercising during hot/humid environ-
ments can be ergogenic (performance
enhancing) for an endurance athlete
(56). In addition to fluid loss, losing
electrolytes from the blood as a person
sweats increases as a concern when
prolonged bouts of exercise are un-
dertaken, and only water is used to
replace lost fluids. This situation can
result in the development of hypona-
tremia (low blood sodium levels) and is
a situation that can result in deleterious
health effects including fainting, seiz-
ures, and death (13,52).
Currently, most commercial carbohy-
drate-electrolyte solutions contain any-
where from 50 to 110 mg of sodium
per 8 fluid ounces. The most practical
advice seems to be for athletes to
weigh themselves before and after an
exercise bout and attempt to keep body
mass losses to no more than 1% when
exercising for greater than 90 minutes
(13,53). Considering the wide varia-
tions in the ambient temperature,
humidity, racecourse topography,
placement of fluid stations, distance
to be covered, and so on makes
additional specific recommendations
challenging to meet all situations.
Minimally, athletes could strive to
consume approximately 100 mL of
fluid every 10 minutes resulting in an
hourly ingestion of 600 mL, an amount
that has been shown to help offset
the magnitude of fluid loss seen when
exercising for prolonged periods in hot
and humid conditions (18) but may not
necessarily be enough to offset de-
velopment of dehydration. Table 2
is provided to illustrate the potential
changes in body weight that can occur,
how quickly it can happen, and how
much fluid is needed to offset this
fluid loss.
CARBOHYDRATE REPLACEMENT
During moderate intensity (e.g., ap-
proximately 65–70%
_
VO
2
max) exercise,
carbohydrate is oxidized at a rate of
1 gram of carbohydrate per minute or
60 grams of carbohydrate per hour
(36,38). When considering that endog-
enous carbohydrate stores can become
severely depleted after 60–90 minutes
of prolonged exercise, replacing lost
carbohydrate is a primary concern for
the endurance athlete. Studies have
illustrated that carbohydrate ingestion
during exercise alters hepatic glucose
Table 1
List of popular supplements that have alleged physiological effects in endurance athletes
Performance-enhancing
ingredients
pH and fluid
modulators
Fuel provision
ingredients Recovery-enhancing ingredients
Acetylcholine b-Alanine a-Lipoic acid 5-HT
Carbohydrate-electrolyte
drinks or gels
Carnosine Branched-chain amino acids Adaptogens (i.e., extracts from Rhodiola rosea,
Cordyceps sinensis,Panax ginseng, and so on)
Citrulline Creatine Caffeine Antioxidants (i.e., vitamins C and E, catechins,
polyphenols)
Creatine Polylactate Carbohydrate/electrolyte
drinks or gels
HMB
Dimethylglycine Sodium tablets Creatine Carbohydrate-protein beverages
Ginseng (i.e., extracts
from Panax ginseng)
Sodium bicarbonate L-Carnitine Colostrum
Coenzyme Q10 Echinacea
Iron Sodium citrate Glycerol GABA
Inosine Medium-chain triglycerides Glucosamine and chondroitin sulfate
Phosphatidylserine Modified corn starch L-Glutamine
Smilax (Sarsaparilla root) Phosphate Ketoisocaproate
Taurine Pyruvate
Ribose 5-HT
Synephrine
5-HT = 5-hydroxytryptophan; HMB = b-hydroxy-b-methybutyrate; GABA = g-aminobutyric acid.
VOLUME 32 | NUMBER 1 | FEBRUARY 2010
56
Supplements for Endurance Athletes

output (8,16), but its impact on muscle
glycogen utilization is equivocal.
Nonetheless, ingesting 30–60 grams
of carbohydrate (in any form except
fructose) per hour during exercise
increases time to exhaustion at
predetermined intensity levels and
time-trial performance of varying dis-
tances (2,5,10,11,23,24,37,45, 48,57,65).
Fructose alone is attributed to gastro-
intestinal distress, decreased perfor-
mance, and lower rates of glycogen
resynthesis, likely because of different
digestive kinetics and absorption
mechanisms when compared with
other forms of carbohydrate (12,22).
For this reason, it is not recommended
to ingest fructose unless it is combined
Table 2
Rate of fluid loss and required fluid replacement
Percent of body mass lost (in lbs)
1% 2% 3% 4%
Body mass (lbs) Pounds of body mass lost
140 1.4 2.8 4.2 5.6
160 1.6 3.2 4.8 6.4
180 1.8 3.6 5.4 7.2
200 2 4 6 8
220 2.2 4.4 6.6 8.8
240 2.4 4.8 7.2 9.6
260 2.6 5.2 7.8 10.4
280 2.8 5.6 8.4 11.2
300 3 6 9 12
320 3.2 6.4 9.6 12.8
340 3.4 6.8 10.2 13.6
Sweat rate
Time (min) 0.5 L/h 1 L/h 1.5 L/h 2 L/h 2.5 L/h 3 L/h 3.5 L/h
Amount of fluid lost (in lbs) according to sweat rate
30 0.6 1.1 1.7 2.2 2.8 3.3 3.9
60 1.1 2.2 3.3 4.4 5.5 6.6 7.7
90 1.7 3.3 5.0 6.6 8.3 9.9 11.6
120 2.2 4.4 6.6 8.8 11.0 13.2 15.4
150 2.8 5.5 8.3 11.0 13.8 16.5 19.3
180 3.3 6.6 9.9 13.2 16.5 19.8 23.1
Cups of fluid needed to replace body mass loss
30 1 234567
60 2 4 6 8 11 13 15
90 3 6 10 13 16 19 22
120 4 8 13 17 21 25 30
150 5 111621263237
180 6 131925323844
Strength and Conditioning Journal | www.nsca-lift.org 57

with other carbohydrate sources
(34,64).
Widrick et al. (65) determined that
preexercise muscle glycogen status and
carbohydrate ingestion improved the
time it took for cyclists to complete
a 70 km self-paced time trial. Through-
out exercise, carbohydrate was in-
gested using a 9% carbohydrate
solution at a rate of 116 66 grams of
carbohydrate per trial. When carbohy-
drate was provided, blood glucose
values were sustained and performance
over the last 14% of the 70 km distance
(or 10 km) was greater (65). Similarly,
when cyclists ingested an 8% carbohy-
drate solution before and every 15
minutes throughout a prolonged exer-
cise bout, cycling time to exhaustion
was extended by 47 minutes or a 30%
increase in endurance (45). Trained
runners also experienced increased
time to exhaustion during an intermit-
tent run to fatigue when ingesting
a 6.9% carbohydrate solution before
and every 15 minutes throughout a 90
minute bout of running at intensities
ranging from ;60% to 90% peak heart
rate (48). Lastly, 2 additional studies
further highlighted the importance of
carbohydrate delivery during endur-
ance exercise.
In the first study, Febbraio et al. (23)
had trained cyclists ride at 63% of peak
power for 120 minutes, followed by
completion of a 7 kilojoules per kilo-
gram of body mass time trial while
ingesting various combinations of car-
bohydrate or placebo before and
during exercise. Only during the 2
conditions where carbohydrate was
ingested during exercise (placebo be-
fore exercise + carbohydrate during
exercise and carbohydrate before ex-
ercise + carbohydrate during exercise)
did performance significantly improve
during the exercise trial (Figure 1) (23).
Fielding et al. (24) reported that a more
frequent intake of a 5% carbohydrate
solution (equal amounts of carbohy-
drate in identical concentrations every
30 minutes or every 60 minutes) was
responsible for an improved mainte-
nance of blood glucose over a 4-hour
bike ride, which resulted in a signifi-
cantly longer ride to exhaustion.
Also, recent studies have suggested
that delivering carbohydrate in the
form of a gel effectively supports
glucose levels in the blood and can
improve performance during a field
soccer test of intermittent running to
exhaustion (50) or prolonged cycling at
75%
_
VO
2
peak (55). Although much of
the published literature using carbohy-
drate involves exercise periods of .60
minutes, recent studies have suggested
that carbohydrate ingestion may also
be beneficial for activities less than
60 minutes in duration (2,57); however,
the number of investigations support-
ing this conclusion is limited at the
current time.
Practically, many commercially avail-
able carbohydrate-electrolyte solutions
(Table 3) deliver carbohydrate solu-
tions at a concentration of 6–8%
carbohydrate (e.g., 6–8 grams of car-
bohydrate for every 100 mL of fluid).
At this concentration, consuming
0.5–1.5 cups (4–12 fluid ounces) of
fluid every 10–15 minutes will replace
the amount of carbohydrate that is
oxidized (11,36) and will also help to
replace lost fluids and electrolytes.
In summary, regular consumption of
a carbohydrate-electrolyte solution can
Figure 1. Performance enhancing effect of carbohydrate ingestion before and during prolonged cycling exercise. Data shown
illustrates the amount of time to complete a standardized amount of work after a 120-minute bout of cycling at 65%
_
VO
2
max under 4 conditions: (a) ingestion of a 25.7% carbohydrate solution before and during the exercise bout (white),
(b) ingestion of a sweet placebo before and a 25.7% carbohydrate solution during the exercise bout (light gray), (c)
ingestion of a 25.7% carbohydrate before exercise and a sweet placebo during the exercise bout (dark gray), and (d)
ingesting a sweet placebo before and during the exercise bout (black). Time to complete a standardized amount of work
(7 kJ/kg body mass) was significantly lower (p,0.05) and indicated by †when the 25.7% carbohydrate solution was
ingested during the exercise bout. Modified with permission from Febbraio et al. (23).
VOLUME 32 | NUMBER 1 | FEBRUARY 2010
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Supplements for Endurance Athletes

be an effective strategy for the endur-
ance athlete to replace lost fluid and
electrolytes, sustain blood glucose,
spare glycogen (66), and promote
greater levels of performance. The
interested reader is encouraged to
consult the following reviews
(18,37,38,59).
CAFFEINE
BACKGROUND
Caffeine is a drug that has been used as
a dietary supplement for its ability to
increase endurance performance, spare
glycogen, promote greater fat oxidation,
prevent fatigue, and reduce perceived
effort (3,9,17,19,21,32,42,44,49,60,62).
Caffeine is an alkaloid present in more
than 60 plant species and reports of its
use as a stimulant goes back several
centuries. It is estimated that the mean
caffeine intake in U.S. adults ranges
from 106 to 170 mg/d (40). Upon
ingestion, caffeine enters the blood-
stream quickly (within 15–45 minutes)
and has a half-life of 2.5–7.5 hours. A
number of studies are available report-
ing ergogenic benefits for caffeine at
doses ranging from 3 to 9 mg/kg
(4,9,19,44,60,62). In addition, caffeine
increases serum levels of catechol-
amines and free fatty acids in the blood
(9), leading to an increase in fat
utilization and a sparing of muscle
glycogen while reducing an individu-
al’s perception of effort (3,19,20,49).
PERFORMANCE
Costill et al. (14) in the late 1970s
demonstrated that subjects drinking
caffeinated coffee before exercise were
able to cycle longer and oxidize more
fat for fuel when compared with
placebo-treated subjects (14). A study
by Graham (26) reported that a caffeine
dose of 3–6 mg/kg increased time to
exhaustion, whereas a 9 mg/kg dose
provided no effect when participants
ran on a treadmill at 85%
_
VO
2
max
until volitional fatigue (26). Doherty
and Smith (19) used a meta-analytic
approach and concluded that exercise
test outcomes were improved by
9.1–15.4% when caffeine supplementa-
tion was provided, and this positive
effect appears to be greater in pro-
longed exercise bouts versus graded
or short-term exercise bouts. In this
regard, when running athletes were
provided a caffeine dose of 3 or 6
mg/kg 1 hour before an exhaustive
running exercise bout, running time
increased from 49.4 to 60 minutes (27)
and when combined with a carbohy-
drate-electrolyte beverage, caffeine, at
a dosage of 195 milligrams of caffeine
for every 1 liter of carbohydrate-
electrolyte solution, has been shown
to improve work capacity by 15% dur-
ing a 15-minute cycling trial after a
135-minute exhaustive ride when com-
pared with a decaffeinated carbohydrate-
electrolyte control beverage (17).
Other studies have reported improved
outcomes relative to rowing perfor-
mance (9), high-intensity cycling (21),
and repeated endurance performance
(4). At lower doses (2–3 mg/kg), the
ergogenic response appears to be more
variable (32), which could be attributed
to the athletes’ normal dietary intake
of caffeine. Finally, after following an
exercise and diet protocol to deplete
muscle glycogen stores, trained cyclists
consumed either a high-carbohydrate
meal (4 grams of carbohydrate for
every kilogram of body mass) or an
identical carbohydrate meal with
caffeine added to the meal at a dosage
of 8 milligrams of caffeine for every
kilogram of body mass. After 1 hour of
recovery, muscle glycogen in both
groups increased similarly, but after
4 hours, muscle glycogen was signifi-
cantly greater when caffeine was added
to the carbohydrate meal, resulting in
a 66% increase in the rate of glycogen
resynthesis (Figure 2; 51). These latest
findings are interesting because they
may suggest an ability of caffeine to aid
in the recovery process in addition to
enhancing performance. However, it is
important that the reader understands
that these findings are the first of such
studies to illustrate an ability of caffeine
when combined with carbohydrate to
promote greater glycogen restoration
and more research needs to be con-
ducted before this recommendation
can be more conclusive.
Caffeine is a banned stimulant at urinary
levels of 12 mg/mL, and for this reason,
it should be used with caution if
Table 3
Nutritional content of commercially available carbohydrate-electrolyte
beverages
Beverage
(per 8 oz) Calories
Carbohydrate
(g)
Carbohydrate
(%)
Sodium
(mg)
Gatorade 50 14 6 110
Powerade 70 19 8 55
All Sport 70 19 8 55
HydraFuel 66 16 7 25
Cytomax 66 13 5 53
Exceed 70 17 7 50
10-K 60 15 6 55
Quickick 67 16 7 100
1st Ade 60 16 7 55
Pedialyte 25 6 2.5 253
Coca-Cola 103 27 11 6
Orange juice 104 25 10 6
Water 0 0 0 Low
Strength and Conditioning Journal | www.nsca-lift.org 59

participating in any National Collegiate
Athletic Association or International
Olympic Committee sanctioned events.
Studies have, however, illustrated that
ergogenic benefits are present with
urinary caffeine levels below the banned
threshold (20,44), but athletes are en-
couraged to use caution when involved
in competition. Reports have contended
that while ergogenic, the diuretic effect
of caffeine should be a primary consid-
eration because of the already rapid fluid
and electrolyte loss that typically occurs
during prolonged exercise in a hot/
humid environment (see above). How-
ever, a review of 10 clinical trials by
Armstrong (1) in 2000 refutes this
suggestion and concluded that at com-
mon caffeine doses (100–680 mg), the
diuretic effect of caffeine was similar to
the diuretic effect from water. Similarly,
this contention was later supported
in a study by Millard-Stafford et al. (46)
that also concluded a caffeine +
carbohydrate solution had no negative
impact relative to hydration, sweat rate,
electrolytes, and other related markers.
ADDITION OF PROTEIN TO
CARBOHYDRATE
BACKGROUND
Making some form of carbohydrate
available, irrespective of type, is an
important consideration for the endur-
ance athlete to restore muscle glyco-
gen. Equally as important are timing
considerations because studies have
illustrated that much of the recovery
ability of the muscle is lost after 2 hours
(29). If rapid recovery is not important,
maximal glycogen restoration may
occur either by regularly (every 15–30
minutes) ingesting carbohydrate at
a dose of 1.2 grams of carbohydrate
per kilogram per hour (84–120 grams
of carbohydrate per hour for individ-
uals weighing 70 to 100 kg, respec-
tively) for several hours (33,61) or to
just simply ingest high dietary levels of
carbohydrate (8–10 grams of carbohy-
drate per kilogram per day or 560–
1,000 grams of carbohydrate per day
for individuals weighing 70–100 kg,
respectively), especially if performing
on consecutive days (39). Adding small
amounts of protein to carbohydrate to
maintain a 3:1 or 4:1 carbohydrate to
protein ratio may help to facilitate
greater performance (31,55) and min-
imize muscle damage (41,54,55) while
also promoting maximal recovery of
muscle glycogen (7,28,30,47,58).
PERFORMANCE
When 3 hours of cycling at 45–75%
_
VO
2
max were followed by a time to
exhaustion trial at 85%
_
VO
2
max, par-
ticipants who consumed a 7.75% car-
bohydrate + 1.94% protein solution (a
4:1 carbohydrate to protein ratio) in
200 mL amounts increased time to
exhaustion (26.9 64.5 minutes) when
Table 4
Practical applications for the use of supplements for endurance athletes
Glycogen stores inside the body are limited and may only last for 60–90 minutes of moderate intensity exercise and depend
largely on body mass, recovery efforts, and training volume/intensity of the athlete. Any athlete who exercises
for this duration will need to replace lost carbohydrate.
The number of available dietary supplements to increase endurance performance continues to grow. Those products,
however, which have been supported by science to increase performance, recovery, or health of an endurance athlete,
are limited.
The premise of dietary supplementation is based on the thought that all athletes and coaches follow sound dietary practices
and is currently getting adequate nutrients from their current dietary regimen. In this respect, all strategies discussed
throughout this article have their limitations because variations in dietary intake and other recovery steps can impact
the efficacy of the discussed strategies.
Athletes and coaches should monitor fluid losses during prolonged exercise bouts in hot/humid environments to determine
the rate at which fluid is lost as sweat from the body because many factors can influence an individual’s sweat rate.
Minimally, consuming 100 mL (;0.5 cups) of fluid every 10 minutes has been shown to help offset fluid losses and is
recommended as a baseline recommendation.
Ingesting 4–12 fluid ounces (;0.5–1.5 cups) of a 6–8% carbohydrate-electrolyte solution every 10–15 minutes during
exercise can serve as an effective means to replace lost carbohydrate, fluid, and electrolytes. Athletes and coaches
need to experiment with what timing and dosing strategies work best and understand that every athlete’s response
is different.
Supplementing with caffeine at a dose of 3–6 mg/kg body mass 30–60 minutes before exercise has been shown to
effectively increase different types of endurance performance. Increased caffeine intake can also increase oxidation of fat,
spare glycogen, and reduce the athlete’s perception of effort.
Adding a small amount of protein to a carbohydrate source has been shown to help restore greater levels of muscle
glycogen, increase performance, and prevent the amount of muscle damage that occurs during a prolonged bout
of endurance exercise.
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Supplements for Endurance Athletes

compared with that of a 7.75% carbo-
hydrate (19.7 64.6 minutes) or a
placebo treatment (12.7 63.1 minutes)
(Figure 3; 31). Interestingly, these
findings were replicated when a carbo-
hydrate + protein gel (0.15 grams of
carbohydrate/kg +0.038 grams of pro-
tein/kg) was ingested versus an iden-
tical carbohydrate gel every 15 minutes
during prolonged endurance exercise
bouts to exhaustion (55). Further,
when a carbohydrate (0.8 grams of
carbohydrate/kg body mass) + protein
(0.4 grams of protein/kg body mass)
solution was ingested immediately
after exercise as part of recovery from
an exhaustive cycling trial, subsequent
performance and power production
Figure 2. Skeletal muscle glycogen content immediately, 1 hour, and 4 hours after a prolonged cycling bout to fatigue at 70%
_
VO
2
peak. Open bars signify 1 gram per kilogram of body mass of carbohydrate consumption, whereas closed bars
indicate carbohydrate + 8 milligram per kilogram of body mass of caffeine consumption. During the carbohydrate-only
trial, boluses were ingested within 5 minutes after exercise and 60, 120, and 180 minutes after exercise. During the
carbohydrate + caffeine trial, subjects followed the same carbohydrate ingestion pattern and a total of 8 milligram per
kilogram of body mass caffeine was given in 2 doses immediately and 2 hours after exercise. * = significant difference
from immediate postexercise (p,0.05); # = significant difference from 1-hour postexercise (p,0.05); †= significant
difference between trials at 4-hour postexercise (p,0.05). Modified with permission from Pedersen et al. (51).
Figure 3. Time to fatigue during a cycling bout at 85%
_
VO
2
max. Before the time trial, subjects exercised for 30 minutes at 45%
_
VO
2
max and performed 15 33 to 8-minute intervals at 75%
_
VO
2
max interjected with 15 33 to 8-minute active
recovery periods at 45%
_
VO
2
max. Following this 180-minute sequence, subjects cycled to fatigue at 85%
_
VO
2
max. Equal
boluses of each supplement were provided at 10-minute intervals over the 180-minute period before the fatigue test.
* = greater than the placebo (p,0.05); †= greater than 7.75% carbohydrate solution. Modified with permission from Ivy
et al. (31).
Strength and Conditioning Journal | www.nsca-lift.org 61

were increased when an additional
exhaustive exercise bout was under-
taken 6 hours later when compared
with carbohydrate ingestion (6).
GLYCOGEN RESYNTHESIS
Adding protein to carbohydrate may
help to promote recovery of lost
muscle glycogen, although these find-
ings are mixed (7,28,30,35,58). For
example, after cycling for 2.5 hours to
deplete muscle glycogen, recovery of
muscle glycogen was measured after
ingesting either carbohydrate or a com-
bination of carbohydrate and protein
(30). After starting with similar levels of
glycogen, cyclists ingested 80 grams of
carbohydrate + 28 grams of protein
+ 6 grams of fat, a lower carbohydrate
(80 grams of carbohydrate) + fat
combination, or a higher carbohydrate
(108 grams of carbohydrate) + fat
combination and the authors found
that muscle glycogen was significantly
higher in the carbohydrate + protein +
fat treatment 4 hours after ingestion
(30). Subsequent studies, however,
have suggested that while high carbo-
hydrate intake (1.2 grams of carbohy-
drate/kg/h or 84–120 grams of
carbohydrate per hour for individuals
weighing 70–100 kg, respectively) may
be all that is needed to promote
maximal glycogen recovery (35,58),
added protein may support muscle
protein synthesis and net protein
balance after exercise (28).
MUSCLE DAMAGE
Additional studies report that a carbo-
hydrate + protein combination, either
in a solution or in a gel, can prevent the
muscle damage associated with pro-
longed endurance exercise when in-
gested during and after prolonged
endurance exercise (54,55). In these
studies, male and female cyclists had
blood levels of creatine kinase, a marker
of muscle damage, determined after
prolonged cycling bouts. The results
indicated that both the carbohydrate +
protein solution and gel significantly
reduced blood levels of creatine kinase
(54,55). Moreover, when 8 endurance
athletes completed approximately 6
hours of exercise at 50%
_
VO
2
max
while ingesting either carbohydrate
(0.7 grams of carbohydrate/kg/h) or
carbohydrate + protein (0.7 grams of
carbohydrate/kg/h + 0.25 grams of
protein/kg/h) every 30 minutes during
exercise, the net protein oxidation rates
(muscle breakdown) were not different
when compared with baseline for
carbohydrate. Carbohydrate + protein
ingestion, however, improved the over-
all net protein balance. Although net
protein balance was still negative,
meaning that more protein breakdown
was occurring than protein synthesis,
these findings suggest that a combina-
tion of carbohydrate + protein may aid
in preventing muscle breakdown and
improve recovery (41).
CONCLUSIONS
Endurance activity places great de-
mands on the metabolic systems of
the human body. Optimal training and
dietary habits are essential for an
athlete to perform at their highest
levels and adequately recovery. Several
dietary supplements are available in
the marketplace targeted to increasing
the performance of endurance athletes.
Many of these, however, lack the
necessary scientific inquiry to be rec-
ommended for their ability to enhance
performance. Practical applications for
the use of supplements for endurance
athletes are presented in Table 4. Much
research is available that supports the
use of carbohydrate-electrolyte solu-
tions before and during a prolonged
exercise bout. These drinks are now
widely available as many commercial
products and are also effective at
maintaining fluid and electrolyte bal-
ance in addition to providing carbo-
hydrate to the body as an energy
source. For more than 40 years,
supplementation with caffeine has
been investigated as an ergogenic aid
and a recent flurry of interest has
reinforced its place as an effective
ergogenic aid for the endurance ath-
lete. Most recently, scientists have
begun to add a small amount of protein
to existing carbohydrate-electrolyte
solutions and have found this addition
can further increase performance,
prevent muscle damage, and assist in
the recovery of muscle glycogen.
Chad Kerksick
is an assistant
professor of exercise
physiology and
director of the
Applied Biochemistry and Molecular
Physiology Laboratory in the Department
of Health and Exercise Science at the
University of Oklahoma in Norman,
Oklahoma.
Mike Roberts is
a doctoral research
and teaching
assistant and
a laboratory
coordinator in the Department of Health
and Exercise Science at the University of
Oklahoma in Norman, Oklahoma.
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