Journal of Strength and Conditioning Research, 2003, 17(1), 187–196
q 2003 National Strength & Conditioning Association
Carbohydrate Supplementation and
G. GREGORY HAFF,1 MARK J. LEHMKUHL,2 LORA B. MCCOY,2 AND
MICHAEL H. STONE3
1Human Performance Laboratory, Midwestern State University, Wichita Falls, Texas 76308; 2Exercise Physiology
Laboratory, Appalachian State University, Boone, North Carolina 28607; 3Sport Science, United States Olympic
Committee, Colorado Springs, Colorado 80909.
There is a growing body of evidence suggesting that the
performance of resistance-training exercises can elicit a significant
glycogenolytic effect that potentially could result in
These decrements may result in
less than optimal physiological adaptations to training. Currently
some scientific evidence suggests that carbohydrate
supplementation prior to and during high-volume resistance
training results in the maintenance of muscle glycogen concentration,
which potentially could result in the maintenance
or increase of performance during a training bout
. Some researchers
suggest that ingesting carbohydrate supplements
prior to and during resistance training may improve resistance-
training performance. Additionally, the ingestion of
carbohydrates following resistance exercise enhances the resynthesis
of muscle glycogen, which may result in a faster
time of recovery from resistance training, thus possibly allowing
for a greater training volume. On the basis of the
current scientific literature, it may be advisable for athletes
who are performing high-volume resistance training to ingest
carbohydrate supplements before, during, and immediately
after resistance training.
Key Words: resistance training, glycogen, glucose, glycogenolytic,
Reference Data: Haff, G.G., M.J. Lehmkuhl, L.B. Mc-
Coy, and M.H. Stone. Carbohydrate supplementation
and resistance training. J. Strength Cond. Res. 17(1):187–
Resistance training has become an integral part of
the training practices of most athletes. With the
increasing popularity of resistance training, many ergogenic
aids and nutritional strategies have been employed
in an attempt to improve performance or increase
muscle growth. Many of these potential aids
have not demonstrated any ergogenic effects.
supplementation is one ergogenic aid that is
not often associated with resistance-training performance
and muscle growth.
supplementation is associated with aerobic exercise
performance. In this context, carbohydrate supplementation
has been shown to increase the amount of work
that can be performed (37, 61, 79) as well as increase
the duration of aerobic exercise (20, 80). The elevation
of blood glucose (BG) associated with supplementation
is suggested to improve aerobic performance
through reduction of muscle glycogen use (3, 5, 80) or
through the use of BG as a predominant fuel source
as glycogen becomes depleted (14, 35, 61).
Evidence presented in the scientific literature suggests
that intermittent activities can stimulate signifi-
cant glycogenolytic effects (6, 70, 78). Because typical
resistance training is intermittent in nature, a similar
effect on muscle glycogen concentration might be expected.
Recently, several studies have reported that resistance-
training bouts can significantly decrease muscle
glycogen stores (25, 54, 67, 72, 73). These investigations
suggest that muscle glycogen is an important
fuel source during resistance-training activities. In
fact, reductions in muscle glycogen concentration have
resulted in accentuated exercise-induced muscle weakness
(80), decreased isokinetic force production (40),
and reduced isometric strength (36). Theoretically, the
implementation of a carbohydrate supplementation regime
may prevent decreases in performance and stimulate
an increase in muscle glycogen resynthesis
This may allow athletes who are performing resistance
exercises to train at higher intensities or perform more
work, thus potentially enhancing the physiological adaptations
that are associated with resistance training.
The purpose of this review is to explore the physiological
and ergogenic effects of carbohydrate supplementation
on resistance-training exercise and identify
future areas of investigation.
Resistance Training and Glycogenolysis
Traditionally, it has been thought that short-duration
high-intensity exercise is primarily supplied with energy
from the muscular stores of phosphagens (adenosine-
triphosphate phosphocreatine system), with glycogenolysis
and glycolysis supplying minimal
amounts of energy (55). Recently, glycogenolysis has
been demonstrated to be an important energy supplier
during high-intensity intermittent exercises, such as
(54, 67, 72, 73).
Recently, Haff et al.
(26) reported that 3 sets of isokinetic leg extensions
performed at 1208·s21 can reduce the muscle glycogen
content of the vastus lateralis by 17%. Additionally, in
the same investigation a multiple-set resistance-training
session (back squats, speed squats, 1-leg squats)
performed at 65, 45, and 10% of 1 repetition maximum
(1RM) back squat resulted in a 26.7% decrease in muscle
glycogen of the vastus lateralis. Tesch et al. (73)
have also reported a 40% reduction in muscle glycogen
in response to the performance of 5 sets of 10 repetitions
of concentric knee extensions performed at 60%
of 1RM. A 30% decrease in the muscle glycogen content
of type IIab and IIb fibers in response to this protocol
was also reported (73). Muscle glycogen concentration
was also reported to decrease by ;20% in response
to the performance of 5 sets of 10 repetitions
at 45% of 1RM. Similarly, Robergs et al. (67) have
shown that 6 sets of 6 repetitions of leg extensions
performed at 70 and 35% of 1RM can elicit a signifi-
cant glycogenolytic effect resulting in 39 and 38% reductions
in glycogen, respectively. Type II fibers were
also demonstrated to have a greater glycogen loss
when compared with type I fibers (67).
Tesch et al. (72)
also reported that a 26% decrease in the muscle glycogen
content of the vastus lateralis can occur in response
to a resistance-training regimen consisting of
5 sets of front squats, back squats, leg presses, and
knee extensions. One set of 10 repetitions of biceps
curls can also reduce muscle glycogen by 13%, whereas
3 sets of 10 can result in a 25% reduction in muscle
glycogen (54). Pascoe et al. (65) have reported a 31%
reduction in muscle glycogen content in response to
leg extensions performed to muscular failure (sets: 8.0
6 0.7). The results of these studies indicate that muscle
glycogen is an important fuel source during resistance
training and suggest that glycogen depletion is dependent
upon the total amount of work accomplished.
Resistance-training sessions that center on higher
repetition schemes (8–12 repetitions) and moderate
loads such as those utilized during the hypertrophy
phase of many athletes and bodybuilders may have a
greater effect on muscle glycogen concentration than
those of lower repetition schemes. However, very little
research has been conducted examining the glycogenolytic
effect of low-volume, heavy-load resistancetraining
Typical high-volume resistance training,
which involves moderate to heavy loads,
seems to preferentially deplete type II fibers. Because
type II fibers usually express higher glycolytic enzyme
activity than do type I fibers, a preferential depletion
of muscle glycogen may not be totally unexpected (23).
The preferential depletion of type II fibers during
high-intensity exercise (24, 78), such as resistance
training, may compromise the performance of highintensity
exercise and ultimately lead to a decrease in
Muscle Glycogen and Carbohydrate Consumption
Reduction in muscle glycogen can potentially result in
reductions in performance. Decreased isokinetic force
production (40), reduced isometric strength (36), and
accentuated muscle weakness (80) have been reported
in the scientific literature in response to reductions in
muscle glycogen. The implementation of a carbohydrate
supplementation regimen may reduce the muscle
glycogen loss associated with resistance-training
bouts. Only 1 published investigation to date has explored
the effects of carbohydrate supplementation on
muscle glycogen loss during a typical resistance-training
bout (26). Haff et al. (26) report that the consumption
of a carbohydrate beverage prior to and during
an acute resistance training bout can attenuate muscle
glycogen loss. In this investigation a carbohydrate beverage
was ingested prior to and every 10 minutes
throughout a free-weight resistance-training bout that
took ;39 minutes. The training bout consisted of 3
sets of 10 repetitions of back squats (65% of 1RM),
speed squats (45% of 1RM), and 1-leg squats (10% of
1RM) and elicited a 26.7% decrease in the muscle glycogen
content of the vastus lateralis with the placebo
treatment. However, the training bout only elicited a
13.7% decrease in muscle glycogen content when a
carbohydrate supplementation regimen was employed.
This decreased rate of glycogenolysis seen with the
carbohydrate treatment may be related to an increased
glycogen synthesis during the rest intervals of intermittent
exercise (52). The results of the study by Haff
et al. (26) suggest that carbohydrate supplementation
prior to and during resistance training can maintain
muscle glycogen stores. Additionally, the inclusion of
a carbohydrate supplementation regimen of the type
used by Haff et al. (26) may be beneficial in the maintenance
of daily glycogen levels, which could potentially
accentuate the benefits of training.
The daily maintenance of glycogen stores appears
to be directly related to the carbohydrates in the diet
(12, 13, 39). The consumption of carbohydrates during
and after exercise will increase the glycogen synthesis
rates following exercise.
Costill et al. (13) have reported
that minimal glycogen synthesis occurs after exercise
when no carbohydrates are consumed. The
amount of muscle glycogen synthesis in the 24-hour
period postexercise is also directly correlated
(r=0.84) to the amount of carbohydrate ingested and the
timing of that ingestion. During the 6 hours postexercise,
a diet consisting primarily of simple carbohydrates
appears to induce a greater glycogen resynthesis
rate. In fact, relatively little glycogen resynthesis
occurs when no carbohydrates are consumed after exercise
(38, 39, 56). When carbohydrates are given immediately
after and 1 hour after resistance exercise, the
muscle glycogen content of the vastus lateralis is returned
to 91% of resting values compared with 75%
of pre-exercise values in 6 hours when only water is
given (65). Thus, delaying the ingestion of carbohydrates
after exercise by as little as 2 hours can significantly
decrease the amount of glycogen resynthesis.
This decrease may be of particular interest to athletes
who perform multiple training sessions on one day. If
the athlete can increase the amount of resynthesis between
exercise bouts, an increase in performance may
occur during the second bout of exercise on a given
Resistance Training and Blood Glucose
A reduction in blood glucose concentration is not normally
experienced during a typical resistance-training
session (26, 28, 43, 58, 67, 75). Keul et al. (43) investigated
the metabolic response of 15 resistance-trained
subjects to a 1-hour training session consisting of the
bench press, deadlift, and squats. No significant
changes in blood glucose levels were noted in response
to the training bout. Similarly, Haff et al. (26) have
reported no significant alterations in blood glucose
levels in response to a 40-minutes free-weight resistance-
training session. Additionally, Haff et al. (28) report
no alterations in blood glucose levels in response
to 57 minutes of isokinetic leg exercise.
Conversely, Vanhelder et al. (75) found that blood
glucose concentration increased in response to 7 sets
of full squats performed at 80% of a 10RM. Haff et al.
(27) have also reported that blood glucose concentrations
increase in response to a resistance-training session
lasting approximately 1 hour. Robergs et al. (67)
examined the metabolic effects of 8 male subjects performing
6 sets of knee extensions at 35 and 70% of
their 1RM. It was determined that following the sixth
set, blood glucose concentration was significantly elevated
when compared with resting values. Two hours
after exercise, blood glucose returned to resting values.
However, blood glucose concentrations at rest, after
the sixth set, and 2 hours after exercise were found to
be similar when accounting for the plasma volume
shift. Additionally, McMillan et al. (58) have reported
that blood glucose concentrations increase as a result
of a resistance-training bout. Similarly, Conley et al.
(11) suggest that blood glucose concentrations were
significantly (p 5 0.001) elevated immediately after exercise,
in response to a resistance-training session. The
blood glucose increases found in these resistance training
studies were similar to those reported for
high-intensity aerobic exercise (80–100% V˙ O2max) (19,
22) and anaerobic cycling (44).
Blood Glucose Response to Carbohydrate Supplementation
There is substantial evidence in the literature to suggest
that the consumption of carbohydrate beverage
before and during resistance training results in elevations
in blood glucose levels during and after the
(11, 26, 28, 29, 51). Haff et al. (28) investigated
the effects of carbohydrate ingestion on 16 sets
of 10 repetitions of isokinetic leg extensions and flexions.
Significantly higher blood glucose levels were
seen at set 8 and immediately after the resistancetraining
bout when subjects consumed a carbohydrate
supplement (20% maltodextrin and dextrose solution)
10 minutes before and after sets 1, 6, and 11 of exercise.
Similarly in another investigation Haff et al. (26)
observed higher blood glucose levels pre-exercise and
immediately after exercises when subjects consumed a
carbohydrate solution (20% maltodextrin and dextrose
solution) 10 minutes before and every 10 minutes during
a resistance-training session.
Additionally, Haff et
al. (29) report significantly higher blood glucose concentrations
immediately postexercise, 1 hour postexercise,
and 2 hours postexercise when subjects consumed
a carbohydrate solution (20% maltodextrin and
dextrose solution) before and after every other set during
the performance of back squats at 55% of their
1RM until voluntary failure.
Conley et al. (11) examined the effect of carbohydrate
ingestion on the performance of multiple bouts
of back squats at 65% of 1RM to voluntary failure.
Blood glucose was found to be significantly higher
during the carbohydrate supplementation (20% maltodextrin
and dextrose solution) trials for the pre-exercise
(p 5 0.036), immediately after (p 5 0.031), and
2 hours after exercise (p 5 0.026) when compared with
the placebo trials.
Lambert et al. (51) examined the effect of carbohydrate
ingestion on the performance of multiple
bouts of leg extensions at 80% of the subject’s 10RM.
Blood glucose was significantly higher (p , 0.05) in
the carbohydrate supplemented (10% glucose polymer)
trials after the seventh set and at failure, when
compared with the placebo trials (51).
It is likely that the elevations in blood glucose seen
with the varying supplementation protocols in the literature
result in either a reduction in muscle glycogen
utilization (3, 5, 80) during the exercise bout or a faster
glycogen resynthesis rate after exercise. When the carbohydrate
supplement is consumed prior to and during
the resistance-training bout, it appears that BG
plays a critical role in fueling glycolysis (51). Additionally,
it is likely that elevations in blood glucose directly
affect the hormonal response to resistance training
Hormonal Responses to Carbohydrate Ingestion
The hormonal responses that occur in response to
acute and chronic resistance training are currently being
investigated (7, 30–34, 50, 58). The addition of a
carbohydrate supplementation regimen to a resistance-
training program may result in an enhanced anabolic
environment. The enhancement of the anabolic
environment could potentially increase muscle hypertrophy
and ultimately increase resistance-training performance
Insulin. Insulin is a polypeptide hormone that is
produced in the b-cells of the islets of Langerhans in
the pancreas. This hormone functions to (a) lower
blood glucose level by enhancing cellular uptake, (b)
enhance the storage of glycogen, (c) enhance fat storage,
(d) enhance cellular uptake of amino acids, (e)
increase the synthesis of proteins, and (f) suppress the
catabolism of proteins (48, 49, 66).
in the concentration of plasma insulin occur in response
to elevations in glucose, amino acids, and fatty
acids (57). Thus, the consumption of a carbohydrate
supplement before and during resistance exercise
might be expected to significantly increase insulin
concentrations. Fahey et al. (18) have demonstrated
that the ingestion of a liquid meal (13 g protein, 32 g
carbohydrate, and 2.6 g of fat) 30 minutes before and
during exercise can significantly increase insulin levels.
Chandler et al. (8) have also reported that the ingestion
of a carbohydrate beverage immediately before
and 2 hours after a resistance-training bout resulted
in significantly higher insulin concentrations when
compared with a placebo beverage. These rises in insulin
theoretically should result in increases in muscle
glycogen stores, protein anabolism, and muscle hypertrophy.
Increases in postexercise insulin levels in
response to carbohydrate ingestion may result in enhanced
glycogen synthesis and an anabolic hormonal
state that potentially could result in an ergogenic effect
Currently, very few studies have investigated this
potential ergogenic effect, and further research is warranted.
Research exploring postexercise carbohydrate supplementation
has suggested that myofibrillar protein
breakdown can be decreased (69). In one investigation
subjects consumed 1 g glucose per kilogram of body
mass immediately after and 1 hour after exercise. The
addition of the carbohydrate supplement resulted in a
significant increase in plasma insulin and glucose concentrations
when compared with a placebo. This finding
was associated with the carbohydrate treatment
eliciting significantly less 3-methylhistidine and urea
nitrogen excretion, which suggests less amino acid
transamination and oxidative deamination occurred.
Additionally, the carbohydrate treatment resulted in a
slightly increased fractional protein synthetic rate. Increases
in insulin are often associated with increases
in amino acid delivery that potentially stimulate increases
in fractional muscle protein synthetic rate and
whole body protein synthesis rate (4). In the study by
Roy et al. (69) the combination of increases in insulin
concentration and fractional protein synthetic rate and
decreases in 3-methylhistidine and urea nitrogen excretion
suggest that carbohydrate supplementation can
result in a reduction of muscle protein degradation after
Recently, Tipton et al. (74) have reported that the
timing of the consumption of a carbohydrate plus amino
acid beverage (CAB) can significantly alter insulin
levels and muscle protein synthesis rates. When the
CAB was ingested prior to the resistance training bout,
significantly greater net protein synthesis and higher
insulin levels were seen when compared with postexercise-
only consumption. This suggests it is possible
that limiting carbohydrate supplementation to the
postexercise period slows net protein synthesis. It is
possible that this effect on net protein synthesis will
be magnified if carbohydrate supplementation is undertaken
before and during the resistance-training
However, no research to date has explored this
On the basis of this limited research it appears that
the inclusion of a carbohydrate supplementation regime
may enhance protein synthesis or decrease muscle
breakdown and ultimately enhance the effects of
resistance training. This may be of particular importance
to the strength athlete who is attempting to promote
muscle growth and possibly enhance overall
muscular strength. Additional research is necessary to
develop a complete understanding of the effects of carbohydrate-
induced insulin increases on muscle hypertrophy
and resistance-training performance.
Growth Hormone. Growth hormone is a polypeptide
hormone that is involved with the growth process of
skeletal muscle and other tissues (49). Increases in
amino acid transport and protein synthesis have been
reported as being stimulated by elevations in growth
hormone (46, 47). Artificial elevations of growth hormone
levels coupled with heavy resistance training are
often associated with increases in lean body mass and
decreases in fat mass (15). Additionally, elevations in
growth hormone levels can be stimulated through the
induction of hypoglycemia by insulin (68). Therefore,
carbohydrate-induced insulin spikes may potentially
lead to increases in growth hormone that may enhance
hypertrophy induced by resistance training.
et al. (8) have reported that supplements that promote
the greatest insulin spike postexercise lead to signifi-
cantly higher growth hormone levels 5–6 hours postexercise
These higher levels of growth hormone only
occurred in carbohydrate and protein-carbohydrate
treatment groups. Additionally, Kraemer et al. (50)
have also reported that growth hormone and insulin
were significantly elevated after day 1 of a 3-day carbohydrate
supplementation and heavy resistancetraining
regime. The combined data of these investigations
lend some support to the concept that insulin
may induce elevations in growth hormone postexercise.
The elevations in growth hormone stimulated by
carbohydrate supplementation may ultimately lead to
increases in muscle hypertrophy and enhanced resistance-
In order to fully understand
these potential ergogenic effects, additional research
exploring the interactions of carbohydrate supplementation,
insulin, and testosterone are warranted.
The steroid hormone cortisol is classified
as a glucocorticoid. This specific glucocorticoid is considered
a catabolic hormone in skeletal muscle (49). As
a catabolic hormone, cortisol stimulates muscle protein
degradation and inhibits protein synthesis in both
type I and type II muscle fibers (41). Cortisol appears
to be highly catabolic in type II fibers and less catabolic
in type I fibers (42). Chronically elevated levels
of cortisol can lead to muscle atrophy and loss of contractile
proteins, which ultimately could reduce
strength levels (21). These negative effects on muscle
fibers may predominate in athletes who perform explosive
strength-training exercises (i.e., power snatch,
power clean, etc.) or participate in sports that require
strength, power, and speed because there is a reliance
on type II fibers (71) in these activities.
Generally, it is believed that the myriad of catabolic
effects stimulated by cortisol occur in order to stimulate
gluconeogenesis (57). The inclusion of a carbohydrate
supplementation regimen may result in a decreased
demand for gluconeogenesis and a concomitant
decrease in cortisol levels.
Additionally, it has
been demonstrated that the lowering of cortisol levels
enhances the release of growth hormone in response
to growth hormone–releasing hormone (17). As stated
earlier, increases in growth hormone may lead to increases
in muscle hypertrophy and resistance-training
performance. Despite these potential benefits, very few
studies have attempted to elucidate the effects of carbohydrate
supplementation on postexercise cortisol
levels. Several studies have demonstrated that the consumption
of carbohydrates during aerobic exercise reduces
postexercise cortisol levels (2, 16, 59). Similar
cortisol responses to carbohydrate supplementation
and resistance training may also be expected. Kraemer
et al. (50) have reported suppressed cortisol levels in
response to 3 days of carbohydrate supplementation
and a heavy resistance-training regime. Additionally,
increases in growth hormone were reported in conjunction
with these suppressed cortisol levels. This
suggests that insulin-mediated suppression of cortisol
may result in increases in growth hormone concentration
and thus lead to an ergogenic effect.
The effects of glucose ingestion during prolonged
endurance exercise on cortisol levels have also been
shown to counteract negative immune changes (63).
Elevations in cortisol levels stimulated by exhaustive
endurance exercise appear to suppress the functioning
of the immune system through a cytotoxic effect on its
cells. Lymphocytes have been shown to be degraded
in the presence of cortisol (10). Additionally, cortisol
has been shown to decrease nucleic acid and protein
synthesis in thymocytes (10). A similar effect might be
expected with high-intensity resistance exercise. In
fact, Nieman et al. (64) have reported that back squats
performed to muscular failure can result in an immune
response that is very similar to that seen with
endurance exercise. Recently, Koch et al. (45) have reported
that the ingestion of a carbohydrate beverage
during a 20-minute resistance-training bout stimulates
a minimal influence on immune response and no effect
on cortisol response when compared with a placebo
treatment. These authors suggest that the short duration
of the training bout induced a stimulus that was
insufficient to significantly elevate cortisol and thus
impact the immune system’s functioning. When contrasting
the cortisol and immune responses of the
studies by Koch et al. (45) and Nieman et al. (64), it is
clear that longer-duration resistance protocols (.35
minutes), such as those that are typically undertaken
in an attempt to induce hypertrophy and are marked
by large training volumes, are needed to significantly
affect cortisol levels and thus the immune system.
The suppression of the immune system may be a
critical issue in the body’s response to muscle damage.
Typically, muscle damage is accentuated by exercises
that have large eccentric muscle action components,
such as resistance training (62). The suppression of the
immune system may increase the recovery time as a
result of an increased time needed to repair muscle
damage. Therefore, the negative effect of cortisol on
the immune system blunted by carbohydrate supplementation
may reduce the time needed to recover
from a typical resistance-training bout. Currently, no
research exists exploring this hypothesis, and further
investigation is needed to fully understand the effects
of carbohydrate supplementation on cortisol and its
relationship to the immune system during resistance
Carbohydrates and Resistance-Training Performance
Research examining the effects of carbohydrate supplementation
on resistance-training performance is
limited and presents conflicting results. Recently, Haff
et al. (26) have reported that carbohydrate supplementation
does not enhance or maintain isokinetic leg exercise
performance. In this investigation, 3 sets of 10
repetitions were performed at 1208·s21 prior to and after
a free-weight resistance-training bout and were
used as a marker of performance. Even though significant
resistance-training regime, the addition of a carbohydrate
supplementation (prior to and every 10 minutes
during the resistance-training bout) did not elicit an
ergogenic effect. However, this result may potentially
be a product of the performance test selected. Recently,
Leveritt and Abernethy (53) have reported that low
levels of glycogen seem to impair the performance of
back squats but have no effects on isokinetic leg exercise.
Thus, it is possible that the maintenance of muscle
glycogen reported by Haff et al. (26) with carbohydrate
supplementation would have resulted in an enhancement
of performance if a different performance
test had been employed.
Increases in resistance-training performance with
carbohydrate supplementation have been reported in
3 investigations presented in the literature. Lambert et
al. (51) have reported that carbohydrate supplementation
prior to and during resistance training can enhance
the performance of sets of 10 repetitions of leg
extensions performed at 80% of 10RM to muscular failure.
In their study each subject participated in 2 testing
trials where they consumed either a placebo or carbohydrate.
The carbohydrate treatment elicited an increased
number of sets (12.7) and repetitions (120).
Similarly, Haff et al. (28) have reported that carbohydrate
supplementation can increase the amount of
work that can be performed during 16 sets of 10 repetitions
of isokinetic leg extensions performed at
Additionally, it was reported that significantly
greater torque was generated by the quadriceps when
the carbohydrate supplement was consumed
significant increases in resistance-training performance
after carbohydrates are consumed during and
between multiple training sessions in one day have
also been reported (29). Two treatment sessions were
conducted in this investigation, in which a carbohydrate
or placebo beverage was consumed. Subjects ingested
these treatments during a 1-hour morning
training session, 4-hour recovery period, and an afternoon
performance test consisting of sets of 10 back
squat repetitions performed at 55% of the 1RM to volitional
failure. The carbohydrate supplementation protocol
used in this investigation resulted in significantly
more repetitions (167.7) and sets (17.4) and greater
exercise duration (131.6 minutes) during the afternoon
performance test. The results of these 3 investigations
seem to support the hypothesis that carbohydrate
supplementation enhances resistance-training
performance. However, it is important to note that all
these studies required the subjects to perform a resistance-
training session that required the performance
of high volumes of work similar to those performed
during the hypertrophy phase of a periodized program
or the typical training of many body builders.
Contrarily, 2 additional investigations have reported
that carbohydrate supplementation does not elicit
an ergogenic effect during resistance training. The first
study, by Conley et al. (11), explored the effects of carbohydrate
supplementation on the performance of sets
of 10 repetitions at 65% of 1RM to volitional failure. A
carbohydrate beverage was consumed 15 minutes before
and after every successful set during testing.
There were no significant differences in the number of
sets or repetitions or total work observed between the
2 treatments. Similarly, it has been reported that carbohydrate
supplementation immediately before a freeweight
resistance-training session consisting of 8 exercises
does not result in an enhanced performance of
isokinetic leg exercise after exercise (76).
The discrepancy between these investigations is
presently unclear. Several distinct possibilities exist for
these differences. The most notable difference between
the studies is the duration of exercise activity. The
studies by Lambert et al. (51), Haff et al. (29), and Haff
et al. (28) showed ergogenic effects when the exercise
bout lasted 56 minutes, 77 minutes, and 57 minutes,
respectively. In contrast, the studies that failed to demonstrate
an ergogenic effect lasted 35 (11) and 39 minutes
(26). Thus it is possible that the duration of the
activity influenced the ergogenic effectiveness of the
Anantaraman et al. (1) have
reported that exercise bouts lasting less than 40 minutes
primarily rely on muscle glycogen as a fuel
source. Thus, as the duration of activity increased, a
greater reduction in muscle glycogen and a greater reliance
on exogenous blood glucose may have occurred.
Secondly, the volume of work performed may be a significant
factor mediating the ergogenic effect of the
carbohydrate supplementation. It is possible that high
volumes of work performed for a duration greater than
40 minutes stimulate a greater stress on the glycogenolytic
system. The 3 studies that demonstrated an ergogenic
effect of carbohydrate supplementation all
lasted longer than 55 minutes and required the subjects
to perform high-volume work with moderate
loads over that time frame. The consumption of a carbohydrate
supplement during this scenario could possibly
spare muscle glycogen (3, 5, 80) or result in BG
becoming the predominant fuel source as glycogen becomes
depleted (14, 35, 61). Thirdly, the exercise test
selected may have resulted in the lack of an ergogenic
effect. Two of the studies that reported no ergogenic
effect utilized an isokinetic performance test. The
study by Vincent et al. (76) utilized a protocol that
required the subjects to perform 3 sets of 15 repetitions
of isokinetic leg exercise at 758·s21 before and after a
free-weight training program. Similarly, Haff et al. (26)
used a testing protocol that required subjects to perform
3 sets of 10 repetitions at 1208·s21 before and after
a free-weight training program. It is possible that the
potential ergogenic effect of carbohydrates would have
been clearer if a different testing protocol had been
Evidence of a lack of impairment in isokinetic
leg exercise performance has been reported in
response to decreased levels of muscle glycogen (53).
Impairments in exercise performance were also seen
in the performance of back squats in the same study.
The only other study to employ an isokinetic testing
bout did, however, exhibit an ergogenic effect (28).
Therefore, the major difference between this study and
those that did not demonstrate an ergogenic effect is
that the study lasted ;59 minutes and employed a
protocol that required ;130 more repetitions. Thus the
increased duration of activity and volume of work may
have mediated the occurrence of an ergogenic effect.
Another explanation for the lack of an ergogenic effect
during isokinetic testing bouts may be that this is a
result of less work being performed during the isokinetic
bout. This may occur because isokinetic devices
are not really isokinetic and force is only applied during
a relatively small range of motion (9, 60). This potentially
could decrease the amount of work performed
and result in a masking of the ergogenic benefit
of carbohydrate supplementation. Additionally,
large-mass exercise may stimulate a greater amount of
glycogen loss in a number of muscles (not just the
prime movers), allowing for an increased ergogenic
benefit from carbohydrate supplementation.
There is limited research exploring the effects of
carbohydrate supplementation on resistance-training
performance. To our knowledge, these are the only investigations
that have attempted to explore the relationship
between carbohydrate supplementation and
resistance-training performance. The data in the literature
seem to suggest that carbohydrate supplementation
has some ergogenic benefits for athletes who are
using high-volume resistance-training protocols similar
to those typically used in the hypertrophy phase
of a periodized training program. However, due to the
limited number of investigations in the literature, this
relationship is still unclear. Further research is necessary
to establish a clearer understanding of this relationship.
Additionally, more research is needed to elucidate
the effect of carbohydrate supplementation on
different types of resistance exercise (i.e., large mass,
small mass, isokinetic, isometric, and isoinertial).
Directions for Future Research
The present body of scientific knowledge suggests that
carbohydrate supplementation can generate several
potential ergogenic benefits for resistance exercise and
At present there exist only a few empirical
studies supporting the use of carbohydrate supplementation
in conjunction with resistance training.
There are several areas related to carbohydrate ingestion
and resistance training that merit further investigation:
1. What is the effect of carbohydrate supplementation
on ability to perform work at different intensities?
Under what conditions will increases in work be
2. What is the relationship between different program
variables (sets, repetitions, and rest intervals) and
modes of resistance training (isotonic, isokinetic, eccentric,
concentric, and isometric)?
3. What are the effects of acute and chronic carbohydrate
supplementation on hypertrophy, body composition,
and athletic performance?
4. What is the effect of carbohydrate-induced insulin
increases on muscle hypertrophy and resistancetraining
5. What are the relationships between carbohydrate
supplementation and the anabolic hormonal environment?
6. What is the potential mechanism for the ergogenic
effects of carbohydrate supplementation during resistance
7. What is the relationship of high-glycemic carbohydrate
supplements to the occurrence of obesity and
8. What are the effects of high-glycemic carbohydrates
supplements on glucose sensitivity of athletes?
Current research strongly suggests that resistance
training, especially using large–muscle mass freeweight
exercises performed with high training volumes
with moderate loads, is partially dependent
upon muscle glycogen stores
. The amount of glycogen
used in these exercises also appears to be related to
the total amount of work accomplished and the duration
of the resistance-training bout. The ingestion of
liquid carbohydrates prior to, during, and after exercise
may serve to promote a faster recovery, which may
enhance subsequent exercise and training sessions
Additionally, the implementation of carbohydrate supplementation
prior to and during a resistance-training
session appears to offer some ergogenic benefit,
through increasing work output when the athlete is
performing high-volume training with moderate
loads. The ingestion of a carbohydrate beverage prior
to and during a resistance-training bout may ultimately
effect the overall net protein synthesis rate
postexercise, which could magnify the hypertrophic
response to training. These potential ergogenic effects
may ultimately result in improved performance during
daily training sessions, which could ultimately enhance
performance in power sports such as football
The literature reviewed suggests that muscle glycogen
plays an important role as a substrate in high-intensity
anaerobic exercise bouts such as resistance training.
This role may be magnified when multiple high-volume
bouts of anaerobic exercise are performed in the
same training day or athletes are participating in a
comprehensive conditioning program that requires intense
exercise on multiple days. The daily maintenance
of glycogen stores may be of crucial importance for
maximizing the performance gains associated with resistance
training or conditioning programs.
mechanism for maintaining daily glycogen
stores is the implementation of a carbohydrate supplementation
regimen. The consumption of a liquid carbohydrate
supplement immediately prior to, during,
and immediately after daily training sessions may offer
some ergogenic benefits to athletes who perform
resistance-training exercises or multiple anaerobic
bouts in the same training day
(i.e., morning resistance
training and evening football practice) or over a training
week. These benefits may include increases in
work output during training, increases in rates of recovery
between training sessions, increases in protein
synthesis rates, maintenance of muscle glycogen
stores, and creation of an anabolic hormonal environment.
All of these benefits could ultimately result in
enhanced muscular strength and hypertrophy, which
are of particular importance to athletes who compete
in sports that require enhanced strength and size, such
as American football. Additionally, the effects of a carbohydrate
supplement’s ability to decrease stress on
the immune system may be of additional benefit to
Therefore it may be advisable for
athletes who are participating in resistance-training
programs for high school, collegiate, and professional
sports to implement a carbohydrate supplementation
program on a daily basis in conjunction with a healthy
diet. This supplementation program should center on
consuming liquid carbohydrates prior to, during, and
immediately after the resistance-training session
whereas the remainder of the carbohydrate consumption,
from the healthy diet, should focus on low-glycemic
carbohydrate sources (fruits, vegetables, and
grains) (77). It is important to make sure that athletes
do not consume the majority of their carbohydrates in
their diet from high-glycemic sources (sugars, candy,
soda, sports drinks, etc.) because this practice may
have some adverse effects on health such as increased
risk of obesity and diabetes mellitus (77). Ultimately,
the implementation of a carbohydrate supplementation
regimen in conjunction with a healthy balanced diet
may result in the enhancement of competition performance
as a result of daily improvements in work output
during training sessions.
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Address correspondence to Dr. G. Gregory Haff,