Effects of creatine supplementation on muscle power, endurance, and sprint performance

Abstract

To determine the effects of creatine (Cr) supplementation (20 g x d(-1) during 5 d) on maximal strength, muscle power production during repetitive high-power-output exercise bouts (MRPB), repeated running sprints, and endurance in handball players.
Nineteen trained male handball players were randomly assigned in a double-blind fashion to either creatine (N = 9) or placebo (N = 10) group. Before and after supplementation, subjects performed one-repetition maximum half-squat (1RM(HS) and bench press (1RM(BP)), 2 sets of MRPB consisting of one set of 10 continuous repetitions (R10) followed by 1 set until exhaustion (R(max)), with exactly 2-min rest periods between each set, during bench-press and half-squat protocols with a resistance equal to 60 and 70% of the subjects' 1RM, respectively. In addition, a countermovement jumping test (CMJ) interspersed before and after the MRPB half-squat exercise bouts and a repeated sprint running test and a maximal multistage discontinuous incremental running test (MDRT) were performed.
Cr supplementation significantly increased body mass (from 79.4 +/- 8 to 80 +/- 8 kg; P < 0.05), number of repetitions performed to fatigue, and total average power output values in the R(max) set of MRPB during bench press (21% and 17%, respectively) and half-squat (33% and 20%, respectively), the 1RM(HS) (11%), as well as the CMJ values after the MRPB half-squat (5%), and the average running times during the first 5 m of the six repeated 15-m sprints (3%). No changes were observed in the strength, running velocity, or body mass measures in the placebo group during the experimental period.
Short-term Cr supplementation leads to significant improvements in lower-body maximal strength, maximal repetitive upper- and lower-body high-power exercise bouts, and total repetitions performed to fatigue in the R(max) set of MRPB, as well as enhanced repeated sprint performance and attenuated decline in jumping ability after MRPB in highly trained handball players. Cr supplementation did not result in any improvement in upper-body maximal strength and in endurance running performance.

Full text

Effects of creatine supplementation on
muscle power, endurance, and sprint
performance
MIKEL IZQUIERDO, JAVIER IBAN
˜EZ, JUAN J. GONZA
´LEZ-BADILLO, and ESTEBAN M. GOROSTIAGA
Centro de Investigacio´n y Medicina del Deporte, Gobierno de Navarra, Navarra, SPAIN; and Centro Olı´mpico de
Estudios Superiores, Comite´ Olı´mpico Espan˜ol, Madrid, SPAIN
ABSTRACT
IZQUIERDO, M., J. IBAN
˜EZ, J. J. GONZA
´LEZ-BADILLO, and E. M. GOROSTIAGA. Effects of creatine supplementation on
muscle power, endurance, and sprint performance. Med. Sci. Sports Exerc., Vol. 34, No. 2, pp. 332–343, 2002. Purpose: To determine
the effects of creatine (Cr) supplementation (20 g·d
⫺1
during 5 d) on maximal strength, muscle power production during repetitive
high-power-output exercise bouts (MRPB), repeated running sprints, and endurance in handball players. Methods: Nineteen trained
male handball players were randomly assigned in a double-blind fashion to either creatine (N⫽9) or placebo (N⫽10) group. Before
and after supplementation, subjects performed one-repetition maximum half-squat (1RM
HS
) and bench press (1RM
BP
), 2 sets of MRPB
consisting of one set of 10 continuous repetitions (R10) followed by 1 set until exhaustion (R
max
), with exactly 2-min rest periods
between each set, during bench-press and half-squat protocols with a resistance equal to 60 and 70% of the subjects’ 1RM, respectively.
In addition, a countermovement jumping test (CMJ) interspersed before and after the MRPB half-squat exercise bouts and a repeated
sprint running test and a maximal multistage discontinuous incremental running test (MDRT) were performed. Results: Cr supple-
mentation significantly increased body mass (from 79.4 ⫾8to80⫾8 kg; P⬍0.05), number of repetitions performed to fatigue, and
total average power output values in the R
max
set of MRPB during bench press (21% and 17%, respectively) and half-squat (33% and
20%, respectively), the 1RM
HS
(11%), as well as the CMJ values after the MRPB half-squat (5%), and the average running times during
the first5mofthesixrepeated 15-m sprints (3%). No changes were observed in the strength, running velocity, or body mass measures
in the placebo group during the experimental period. Conclusion: Short-term Cr supplementation leads to significant improvements
in lower-body maximal strength, maximal repetitive upper- and lower-body high-power exercise bouts, and total repetitions performed
to fatigue in the R
max
set of MRPB, as well as enhanced repeated sprint performance and attenuated decline in jumping ability after
MRPB in highly trained handball players. Cr supplementation did not result in any improvement in upper-body maximal strength and
in endurance running performance. Key Words: STRENGTH, MUSCLE POWER OUTPUT, ENDURANCE, CREATINE
During intense exercise of short duration, the adeno-
sine triphosphate (ATP)-phosphocreatine (PCr) sys-
tem is the predominant energy supplier for muscu-
lar work (15). When PCr becomes depleted, performance
deteriorates because ATP cannot be resynthesized at the rate
required (12,15,19,21). This has led to some authors to
suggest that increasing resting levels of PCr availability
after oral creatine (Cr) loading might delay PCr depletion
and attenuate the decline in ATP provision during intense
exercise or might accelerate the rate of PCr resynthesis after
intense repeated exercise (12,19,21). It has been shown that
oral Cr supplementation, in amounts substantially in excess
of the normal dietary intake, can elevate the whole-muscle
total Cr stores by approximately 20%, one third of which is
in the form of PCr (12,14). Several studies have shown that
short-term Cr supplementation may enhance the athlete’s
capacity to perform repeated muscular actions or bouts of
high-intensity exercise and maintain power output as well as
delay onset of muscular fatigue, in addition to promoting
faster recovery between bouts of intense exercise
(4,8,11,21,38). However, other studies on creatine supple-
mentation failed to show any potentially positive effects
(10,25,30,36).
High-intensity resistance exercise may benefit from Cr
loading because energy-rich phosphates significantly con-
tribute to the energy yield during resistance tasks (23). Few
studies have reported the short-term (⬍1 wk) effects of Cr
supplementation on dynamic and constant resistance exer-
cise (3). For instance, Volek et al. (37) showed that short-
term Cr supplementation resulted in a significant improve-
ment in the highest recorded peak power output achieved for
a single repetition during all 5 sets of jump squats and a
significant improvement in the number of repetitions during
bench presses. To the authors’ knowledge, no studies have
reported the short-term (⬍1 wk) effects of Cr supplemen-
tation on the power output generated during maximal repet-
itive muscle contractions of the lower- and upper-extremity
muscles in two resistance exercises with training loads typ-
ically undertaken by athletes (i.e., bench-press and half-
squat exercises; 60–70% of 1RM). Therefore, one purpose
of this study was to examine the effects of short-term Cr
supplementation on maximal strength and muscular power
0195-9131/02/3402-0332/$3.00/0
MEDICINE & SCIENCE IN SPORTS & EXERCISE
®
Copyright © 2002 by the American College of Sports Medicine
Submitted for publication February 2001.
Accepted for publication May 2001.
332

output during repeated sets of repetitive bouts of high-
intensity power output of bench-press and half-squat exer-
cise in highly trained handball players.
Moreover, the ability of creatine supplementation to im-
prove performance and energy metabolism during weight-
bearing activities as such repeated sprint runs (1,27,31,34)
or during endurance exercise (4,27,33) remains controver-
sial. Therefore, the second purpose of this study was to
examine the effects of short-term Cr supplementation on
repeated sprint runs and endurance performance in handball
players. We choose handball players to investigate the ef-
fects of Cr loading on muscle power output, sprint perfor-
mance, and endurance because during handball training and
competition they perform frequent strenuous activities, such
as repeated bouts of various sprints, throws, and jumping
performances, interspersed with aerobic recovery periods
(2). Accordingly, it was hypothesized that oral Cr supple-
mentation could enhance performance during repeated
sprints runs and during training-specific repetitive high-
intensity power output exercise bouts, without having a
detrimental effect on endurance running.
METHODS
Subjects
Nineteen experienced male handball players volunteered
to participate in the study. All the subjects were members of
the same team, played in the Spanish second division, and
had a minimum continuous handball training background of
14.5 ⫾2 yr of experience before the study. The subjects
were trained by the same coach over the last 3 yr. This study
was performed in February, during the competitive season
(October to May), in the only week where no official game
was played. During the 5 months before the beginning of the
experimental period, the subjects trained four times a week
for handball, once a week for strength and endurance train-
ing, and played in one official handball game per week.
During the experimental period (in the only week where no
official game was played), only the test procedures, as well
as two practice handball sessions were carried out. The last
strength-training session took place 5 d before the pretest.
Practice handball sessions lasted 90 min and usually con-
sisted of various skill activities at different intensities, of-
fensive and defensive strategy, and 30 min of continuous
play with only brief interruptions by the coach. The
strength-training sessions were performed immediately be-
fore the handball training sessions. The strength-training
program required each subject to perform a combination of
free weights and exercise machines in each session, mainly
consisting of 3 sets of 10–12 RM. The exercises completed
in each weight-training session were the supine bench press,
half-squat, and knee flexion curl. The total duration of each
strength-training session was 35–40 min. The running en-
durance program consisted of one training session per week
and lasted 20–30 min at a self-adjusted intensity. Only
subjects that had never been supplemented with creatine
monohydrate/maltodextrin or had never used anabolic ste-
roids or beta-agonists were eligible for participation to avoid
unknown subsequent physiological adaptations; the subjects
were aware of their supplementation condition. After base-
line testing, subjects were matched according to physical
characteristics, muscle strength/power, velocity, and endur-
ance indices and then randomly assigned in a double-blind
fashion into a creatine (N⫽9) and placebo (N⫽10) group.
They were informed carefully on the experimental proce-
dures and about the possible risks and benefits of the project
design. The experimental procedures were approved by the
Institutional Review Committee of the Instituto Navarro de
Deporte y Juventud, according to the declaration of Hel-
sinki. Each subject signed a written informed consent form
before participation in the study.
Experimental Design
This study utilized a two-group matched, doubled-blind,
randomly assigned design. Subjects completed a 2-d exper-
imental protocol on two different occasions separated by
7 d, before the 5-d supplementation period and at the end.
Body weight and body fat estimates from the measurements
of seven skin-fold thickness (17) were taken at the begin-
ning of both testing sessions. During the first testing session,
each subject was tested for his one concentric repetition
maximum (1RM) from a bench-press (1RM
BP
) and half-
squat (1RM
HS
) position. After 1RM testing, the subjects
performed maximal repetitive high-power-output exercise
bouts with submaximal loads during a bench-press and
half-squat protocol. The countermovement jumping test was
interspersed before and 3–7 s after the maximal repetitive
high-power-output half-squat exercise bouts. In the second
test session, each subject performed a repeated sprint run-
ning test (RPRT) followed by 10 min of rest for a maximal
multistage discontinuous incremental running test (MDRT).
For a given subject, muscle strength and endurance tests
took place at the same time of day throughout the experi-
ment. All the subjects were familiarized with the testing
protocol, as they had been previously tested on several
occasions during the season with the same testing proce-
dures. The test-retest intraclass correlations coefficients of
the testing procedure variables used in this study were
greater than 0.91, and the coefficients of variation (CV)
ranged from 0.9% to 7.3% (unpublished results).
Performance Testing
Maximal strength and muscle power output. Dur-
ing the first test session, lower- and upper-body maximal
strength was assessed using one-repetition concentric max-
imum bench-press (1RM
BP
) and half-squat (1RM
HS
)ac
-
tions. In 1RM
BP
protocol the bar was positioned 1 cm above
the subject’s chest and supported by the bottom stops of the
measurement device. The subject was instructed to perform,
from the starting position, a purely concentric action main-
taining the shoulders in a 90°abducted position to ensure
consistency of the shoulder and elbow joints throughout the
testing movement. No bouncing or arching of the back was
allowed. In 1RM
HS
protocol the shoulders were in contact
CREATINE AND REPETITIVE EXERCISE PERFORMANCE Medicine & Science in Sports & Exercise姞
333

with a bar and the starting knee angle was 90°. On command,
the subject performed a concentric leg extension (as fast as
possible) starting from the flexed position to reach the full
extension of 180°against the resistance determined by the
weight plates added to both ends of the bar. The motion was
completed when the torso was upright. All the tests were
performed in a squatting apparatus in which the barbell was
attached to both ends, with linear bearings on two vertical bars
allowing only vertical movements. Warm-up consisted of a set
of 5 repetitions at the loads of 40–60% of the perceived
maximum. Thereafter, four to five separate single attempts
were performed until the subject was unable to extend the legs
or arms to reach the full extension. The rest between maximal
attempts was always 2 min.
Maximal repetitive high-power-output exercise
bouts with submaximal loads. After 5-min rest, the
subjects performed a maximal-repetitive high-power-output
exercise bouts with submaximal loads during half-squat and
bench-press protocols. The bench-press protocol consisted
of one set of 10 continuous repetitions (R10) with a resis-
tance equal to 60% of the subject’s 1RM
BP
, followed by one
set until fatigue (R
max
), with exactly 2-min rest periods
between each set. The half-squat protocol consisted of one
set of 10 continuous repetitions with a resistance equal to
70% of the subjects’1RM
HS
, followed by one set until
fatigue with the same load, with exactly 2-min rest periods
between each set. The subjects were asked to move the bar
as fast as possible during the concentric and eccentric phase
of each repetition, until they were unable to reach the full
extension position of the arms or legs. Fatigue was defined
at the time point when the bar ceased to move, if the subject
paused more than 1 s when the legs or arms were in the
extended or flexed position, or if the subject was unable to
reach the full extension position of the arms or legs. The
cadence of each repetition was controlled with a metronome
with a frequency of 19 Hz.
During the upper- and lower-extremity test actions, bar
displacement, average velocity (m·s
⫺1
), and mean power
(W) were recorded by linking a rotary encoder to the end
part of the bar. The rotary encoder recorded the position and
direction of the bar within an accuracy of 0.2 mm and time
events with an accuracy of 1
␮
s. Customized software
(JLML I⫹D, Madrid, Spain) was used to calculate the
power output for each repetition of half-squat and bench-
press performances throughout the whole range of motion
used to perform a complete repetition.). The velocity (v;
m·s
⫺1
) was calculated each instantaneous displacement (⌬d)
of 0.2 mm by using the following equation:
V⫽⌬d䡠⌬t⫺1,
where ⌬t is the time (s) to perform the instantaneous range
of displacement (0.2 mm) with a resolution of 1
␮
s. The
calculation of instantaneous power was then calculated by
multiplying the velocity over each displacement period by
force derived from the product of mass of the load and
acceleration due to gravity. Average power for each repe-
tition was calculated as the means of all instantaneous power
values measured during all the time necessary to perform a
complete repetition. Total repetitions for each set of bench
presses and average power output for each repetition of
half-squat and bench press were determined. The average
power value obtained for each repetition was used to cal-
culate the total average power generated during each set of
exercise in both groups. Power curves were plotted using
average power over the whole range of movement as the
most representative mechanical parameter associated with a
contraction cycle of each muscle group.
Jumping test. Before 1RM half-squat assessment and
after completion of each set of the half-squat protocol,
subjects were instructed to walk to the contact platform
(Newtest Oy, Oulu, Finland) situated close to the barbell and
immediately perform two maximal countermovement jumps
(CMJ). The time delay between finishing the half-squat
protocol and performing the first jump was between 3 and
7 s. The second jump was always performed 4 s after the end
of the first jump. The subjects were asked to perform a CMJ
on the contact platform with a preparatory movement from
the extended leg position down to the 90°knee flexion,
followed by a subsequent concentric action. The jumping
height was calculated from the flight time. Two maximal
jumps were recorded interspersed with approximately 10 s
of rest and the peak value was used for further analysis.
Repeated sprint runs. The repeated sprint runs
(RPRT) and the endurance running tests were performed in
the second test session, at the same time of day, and in the
same indoor handball court. After a standardized 15-min
warm-up period that included low-intensity running, several
acceleration runs, and stretching exercises, the subjects un-
dertook a sprint running test consisting of six maximal
sprints of 15 m, with a 60-s rest period between each sprint.
Stance for the start was consistent for each subject. During
the 60-s recovery period, the subjects walked back to the
starting line. The recording of running time was done by
using photocell gates (Newtest Oy), placed 0.4 m above the
ground and placed at 0.5 m, 5.5 m, and 15.5 m.
Endurance running test. Ten minutes after the end of
the RPRT test, the subjects performed a maximal discon-
tinuous incremental running test (MDRT) around the hand-
ball court (40 ⫻20 m) until volitional exhaustion. The
initial velocity was 10 km·h
⫺1
and then was increased in a
step-wise fashion by 2 km·h
⫺1
every 5 min, until volitional
exhaustion or the required running velocity could not be
maintained. After each stage, the test was interrupted for 3
min before initiating the next stage. To assure a constant
velocity for each running stage, the subjects were instructed
to pace their running through an audio signal connected to
a preprogrammed computer (Balise Temporelle, Bauman,
Switzerland). During the test, heart rate was recorded every
15 s (Polar Vantage NV, Polar Electro, Kempele, Finland)
and averaged for the last 60 s of each stage. Immediately
after each exercise stage, capillary blood samples for the
determination of lactate concentrations were obtained from
a hyperemic earlobe. Samples for the whole blood lactate
determination (100
␮
L) were deproteinized, placed in a
preservative tube (YSI 2315 Blood Lactate Preservative Kit,
Yellow Springs, OH), stored at 4°C, and analyzed (YSI
334
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1500) within 5 d after completing the test. According to the
manufacturer’s instructions, placing the capillary samples in
these preservative tubes allows the blood samples to be
stored for 3–5 d with stable blood lactate concentration
values (pooled estimate of standard deviation: 0.15
mmol·L
⫺1
for a concentration range of 0–10 mmol·L
⫺1
).
The blood lactate analyzer was calibrated after every fifth
blood sample dosage with three known controls (5, 15, and
30 mmol·L
⫺1
).
Urinary Creatinine
Twelve-hour overnight urine samples were collected in
containers the day before and the morning after5dof
treatment. After collection, all samples were measured for
urinary volume, and mixed samples were immediately an-
alyzed for urinary creatinine concentration by spectropho-
tometry using a Synchron CX7 apparatus (Beckman Instru-
ments Inc., La Brea, CA).
Supplementation Procedure
After baseline testing, subjects were asked to consume
either5gofcreatine monohydrate (Cr, N⫽9) or an
equivalent volume of maltodextrin (placebo, N⫽10), four
times daily for the next 5 d. Each supplement was measured
using electronically calibrated scales and placed in identical
coded airtight bags. The subjects mixed the supplement
powder in approximately 0.25 L of warm-to-hot water for
better dissolution of creatine (14) and ingested the solution
with morning, mid-day, afternoon, and evening meals. Cr
and placebo were administered in a double-blind fashion.
The supplementation was initiated right after the baseline
testing and ended the same day of the first performance
testing postsupplementation session. This dosage pattern of
creatine administration was chosen because it has been
shown to produce significant increases in resting muscle
PCr levels in men (14). Compliance with the supplement
was 100%. We also assessed creatinine urinary levels to
support this approach. When asked verbally at the end of the
study, the subjects did not know the supplementation they
had received.
Statistical Methods
Standard statistical methods were used for the calculation
of the means and standard deviations. A t-test for unpaired
samples indicated that there were no baseline differences
among the two groups’initial maximal strength, repetitive
high-power-output exercise bouts, number of repetitions
during a half-squat and bench press, and endurance and
sprint running measures. Corresponding pre- and post-sup-
plementation values for all measured variables were com-
pared via a two-way analysis of variance (ANOVA, group
⫻time) with repeated measures design. When a significant
F-value was achieved, Scheffe´post hoc procedures were
performed to locate the pairwise differences between the
means. The Pⱕ0.05 criterion was used for establishing
statistical significance.
RESULTS
Body Mass
The physical characteristics of the creatine and placebo
groups were (mean ⫾SD): age, 20.8 ⫾5 and 23.6 ⫾5 yr;
height, 182 ⫾8 and 189.7 ⫾8 cm; body mass 79.4 ⫾8 and
87 ⫾12 kg; percent body fat, 10.7 ⫾3 and 11.3 ⫾3%,
respectively. No significant differences between the two
groups were noted in age, height, body mass, and percent
body fat at presupplementation measurement. There was
significant group ⫻time interaction, with significantly
greater (P⬍0.01) increases in body mass after supplemen-
tation in Cr group than in the placebo group. In the Cr
subjects, body mass increased significantly (P⬍0.05) from
79.4 ⫾8to80⫾8 kg, during the supplementation period.
No significant changes were observed in the body mass of
the placebo subjects throughout the experimental period (87
⫾12 and 86.8 ⫾11 kg, before and after the supplementa-
tion period, respectively). No significant change in percent
body fat was observed in the creatine (10.7 ⫾3 and 10.3 ⫾
3%) and placebo groups (11.3 ⫾3 and 10.9 ⫾3%, before
and after the supplementation period, respectively).
Maximal Strength
Maximal 1RM
BP
and 1RM
HS
values are shown in Figure
1. Neither group showed significant changes in the maximal
1RM
BP
after the supplementation period. There was signif-
icant group ⫻time interaction, with significantly greater (P
⬍0.01) increases in 1RM
HS
in Cr group than in the placebo
group. In Cr subjects, 1RM
HS
increased significantly from
133 ⫾11.9 to 147.7 ⫾14.1 kg (P⬍0.001) during the
supplementation period. In contrast, no significant changes
were observed in the 1RM
HS
of the placebo subjects
throughout the experimental period.
Maximal repetitive high-power-output exercise
bouts with submaximal loads. The data for average
power produced pre- and post-supplementation produced
during each repetition of bench press (60% of 1RM
BP
)
during the R10 and R
max
sets are presented in Figure 2.
After the initial maximum, average power production in the
bench-press action declined consistently and followed the
same pattern in both groups during the R10 set (Fig. 2, A
and B). In both groups, there were no differences in the
individual average power for each repetition and in the total
average power values during the R10 set of the bench-press
action, before and after the supplementation period. A sig-
nificant group ⫻time interaction was found in the R
max
set,
with a significantly greater (P⬍0.05–0.01) mean improve-
ment in the number of repetitions and total average power
production values of repetitions performed to fatigue after
Cr supplementation compared with the placebo group. Dur-
ing the second set (R
max
) of the bench press, no significant
changes were observed for the placebo group before and
after the supplementation period in average muscle power
output in each repetition, in the total average power output
values of repetitions performed to fatigue (240 ⫾35,2 vs
236 ⫾42 W), and in the number of repetitions to fatigue
CREATINE AND REPETITIVE EXERCISE PERFORMANCE Medicine & Science in Sports & Exercise姞
335

(15.7 ⫾3.8 vs 16.8 ⫾4.9, pre- and post-supplementation,
respectively) (Fig. 2C). Creatine supplementation consis-
tently increased posttreatment total average muscle power
output performed to fatigue (248 ⫾49 vs 262 ⫾63 W; P⬍
0.05, pre- and post-supplementation, respectively) and the
number of repetitions to fatigue (16.1 ⫾2.9 vs 18.8 ⫾3.5;
P⬍0.05, before and after supplementation, respectively) in
R
max
set of the bench press.
The data for the average power produced pre- and post-
supplementation during each repetition in the half-squat
action (70% of 1RM
HS
) during the R10 and R
max
sets are
presented in Figure 3. In both groups, there were no differ-
ences in the individual average power produced for each
repetition during R10 and R
max
sets of the half-squat action,
before and after supplementation. There was a significant
group ⫻time interaction for the total average power pro-
duction values of repetitions performed in the R10 set of the
half-squat performance; the mean improvement in total av-
erage power production values in Cr group was significantly
greater (P⬍0.01) after supplementation than in the placebo
subjects. In the placebo group, there were no significant dif-
ferences in the total average power produced values performed
in R10 set of the half-squat, before and after supplementation
(Fig. 3A). However, after5dofCringestion, the total average
power produced values (557 ⫾107 vs 605 ⫾123 W, P⬍
0.01) performed in R10 set of the half-squat were significantly
greater than before supplementation (Fig. 3B).
A significant group ⫻time interaction was observed for
the number of repetitions and total average power produc-
tion values of repetitions performed to fatigue in the half-
squat action. For the Cr group, the mean improvement in the
number of repetitions and total average power production
values of repetitions performed to fatigue was significantly
greater (P⬍0.01) after supplementation than in the placebo
subjects. During the R
max
set of the half-squat, no signifi-
cant changes were observed before and after the supplemen-
tation period for the placebo group, in average muscle
power output in each repetition, the total average power
output values of repetitions performed to fatigue (514 ⫾107
vs 520 ⫾108 W, pre- and post-supplementation), and in the
number of repetitions to fatigue performed with the 70% of
1RM
HS
(13.8 ⫾5 vs 13.5 ⫾4.4 pre- and post-supplemen-
tation, respectively) (Fig. 3C). Creatine supplementation
consistently increased posttreatment total average power
output values of repetitions performed to fatigue (514 ⫾99
Wvs566⫾118 W; P⬍0.001, pre- and post-supplemen-
tation respectively) and the number of repetitions to fatigue
(13.2 ⫾3.0 vs 15.9 ⫾2.1; P⬍0.01, before and after
supplementation, respectively) in R
max
set of the half-squat
(Fig. 3D).
Countermovement jump (CMJ). Figure 4 shows the
countermovement vertical jump values (CMJ) at rest, at the
end of R10 set of the half-squat (PostR10), and at the end of
R
max
set of the half-squat (PostR
max
), in the placebo group
(Fig. 4A) and in the Cr group (Fig. 4B). Significant group ⫻
time interaction was observed for the CMJ at post R10 (P⬍
0.01). Thus, for the Cr group, the mean change in the CMJ
values at PostR10 decreased to a lesser extent (P⬍0.05)
after supplementation compared with the placebo subjects.
At the end of the first (PostR10) and the second (PostR
max
)
set repetitions of the half-squat, a significant decline in CMJ
values was observed in both groups. However, an attenuated
decline in jumping ability was observed in the Cr group after
the first set of 10 repetitions. Thus, the CMJ values at the
end of the first set of 10 repetitions of the half-squat were
enhanced after Cr supplementation (from 31.4 ⫾1 to 33.1
⫾1 cm; P⬍0.05, pre- and post-supplementation, respec-
tively), whereas the placebo group’s jumping height re-
mained unchanged (30.1 ⫾1 vs 30.3 ⫾1 cm, pre- and
post-supplementation, respectively). In the placebo and Cr
subjects, there were no significant changes in the jumping
height reached after the completion of the set of maximum
repetitions to fatigue (PostR
max
) in a half-squat action.
Repeated sprint runs. The run time remained con-
stant during the repeated maximal-effort 15-m sprints. Cre-
atine supplementation did not improve average running
FIGURE 1—One-repetition maximum (1RM) bench press and half-
squat before and after the creatine or placebo supplementation period.
*** Denotes a significant difference between pre-and post-supplemen-
tation (P<0.001). Values are means ⴞSD. Significant pre-/post-
supplementation differences were tested after a significant (group ⴛ
time) interaction was found. See text for details.
336
Official Journal of the American College of Sports Medicine http://www.acsm-msse.org

times for 15-m repeated sprints but did improve running
time on the first5mofthe15-m repeated sprints (Fig. 5).
There was a significant group ⫻time interaction, with a
significantly greater (P⬍0.05) mean improvement in the
average running time for 5-m distance after Cr supplemen-
tation compared with the placebo group. Average running
times for 5-m distance of the six repeated sprints also
improved significantly (P⬍0.05) in the Cr group from 1.05
⫾0.03 to 1.03 ⫾0.03 s pre- and post-supplementation,
respectively. In the placebo group, no significant improve-
ment was observed at the 5- and 15-m sprint running times
throughout the experimental period.
Maximal incremental endurance running test.
The values of the average blood lactate concentration–run-
ning velocity curves differed between the groups (Fig. 6). A
significant decrease in mean blood lactate concentration was
observed in the placebo group at running velocities of 10
km·h
⫺1
(from 2.2 ⫾1.1 to 1.8 ⫾1 mmol·L
⫺1
,P⬍0.05)
and 12 km·h
⫺1
(from 3.1 ⫾1.6 to 2.7 ⫾1.6 mmol·L
⫺1
,P⬍
0.01), before and after supplementation, respectively (Fig.
6A). No significant changes were observed in mean blood
lactate concentrations in the Cr group at these velocities
(Fig. 6B). In the placebo group, mean decreases in blood
lactate at running velocities of 12 km·h
⫺1
were significantly
greater (P⬍0.05) than in the Cr group. Average time to
exhaustion attained during the MDRT was unchanged in the
placebo group (1181 ⫾158 vs 1166 ⫾161 s) and in the
creatine group (1163 ⫾125 vs 1152 ⫾133 s). The maximal
values of blood lactate concentration and heart rate re-
mained unaltered throughout the study in both groups. No
significant differences were observed in time to exhaustion
between groups.
Urinary Creatinine
There was a significant group ⫻time interaction, with
significantly greater (P⬍0.05) average increases in urinary
creatinine in the Cr group compared with the placebo group,
urinary creatinine excretion increased significantly in the
creatine group (141 ⫾53, vs 248.9 ⫾76.1 mg·dL
⫺1
;P⬍
0.001), whereas it remained unchanged in the placebo group
(155.7 ⫾67.7 vs 157.6 ⫾58.9 mg·dL
⫺1
) after5dof
supplementation. Urinary volume remained unaltered after
5 d of supplementation in either the placebo (45.6 ⫾25.2 vs
FIGURE 2—Average muscle power pre- and post-supplementation for each repetition during a bench-press exercise during a set of 10 repetitions
(R10; A and B), followed after a 2-min rest by a set of maximum repetitions to fatigue (R
max
; C and D) with the 60% of 1RM bench press. Values
are means ⴞSD. The data points correspond to the average power output for each repetition of bench press during an R10 set (A and B) and to
the average power output for each repetition that were completed by all subjects during an R
max
set (C and D). The stand-alone points in panels
C and D correspond to the average power output for the last repetition performed for each subject in an R
max
set.
CREATINE AND REPETITIVE EXERCISE PERFORMANCE Medicine & Science in Sports & Exercise姞
337

56.7 ⫾20 mL·h
⫺1
) and the creatine subjects (50.2 ⫾15
vs 41.6 ⫾15 mL·h
⫺1
) pre- and post-supplementation,
respectively.
Side Effects
No reports of gastrointestinal distress and/or medical
problems/symptoms were observed during the supplemen-
tation period. There was no evidence of muscular cramping
or muscle injury during handball training and games or
during testing trials.
DISCUSSION
The present study demonstrated that short-term Cr sup-
plementation (20 g·d
⫺1
for 5 d) led to significant improve-
ments in lower-body maximal strength, maximal repetitive
upper- and lower-body high-power exercise bouts, and total
repetitions performed to fatigue during sets of bench-press
and half-squat actions in highly trained handball players.
The enhancement was more marked in the lower- than in the
upper-extremity muscles. Creatine-supplemented handball
players showed improved performance during the first 5 m
of repeated bouts of 15-m sprint runs, as well as an atten-
uated decline in jumping ability after submaximal repetitive
high-power-output half-squat exercise bout. Furthermore,
the present results show that Cr supplementation did not
result in any improvement in upper-body maximal strength
and in endurance running exercise.
A significant improvement after short-term Cr supple-
mentation has been previously reported in the number of
repetitions completed during multiple sets of isotonic
bench-press (37) and isokinetic, concentric-only, knee-ex-
tension contractions (11). The present study demonstrated
that in trained subjects Cr supplementation significantly
enhanced maximal repetitive power production during sets
of bench-press and half-squat resistance exercises. This con-
firms the finding of Volek et al. (37) with jump squats and
Greenhaff et al. (11) with isokinetic knee-extension con-
tractions that short-term Cr supplementation may improve
muscle power output during repetitive bouts of resistance
exercise (39). Although muscle creatine concentration was
not measured in the present study, the increased ability of
the Cr group to perform a greater total lifting volume and
generate more total average muscle power suggests that
FIGURE 3—Average muscle power pre- and post-supplementation in each repetition during a half-squat press exercise during a set of 10 repetitions
(R10; A and B), followed after a 2-min rest by a set of maximum repetitions to fatigue (R
max
; C and D) with the 70% of 1RM half-squat. Values
are means ⴞSD. Data points are as described in Figure 2.
338
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creatine loading appears to enhance muscular performance
during intermittent resistance exercise. This increased ca-
pacity to perform more repetitions and generate more power
output may reflect increases in intramuscular PCr stores
(14), increased ATP provision and attenuated reduction in
ATP with repeated work tasks (11,13,20), a reduction of
muscle adenine nucleotide loss (11), an increased velocity
of PCr resynthesis during recovery periods after muscle
contractions (11,13,20), and an increased potential for PCr
to work as an ion H⫹buffer (18). It is also likely that this
ability to perform greater muscle power during a resistance-
training session after Cr supplementation may allow athletes
to complete their workouts at a higher intensity (3,38) and
increase their adaptive responses in muscular structure and
function (8).
After5dofCrsupplementation, a significant acute in-
crease (11%) was observed in 1RM half-squat, whereas it
remained unaltered in the placebo group. An explanation of
this unexpected finding is difficult to interpret because in-
creases in maximal muscular strength (1RM) are generally
not thought to be limited by phosphagen metabolism (38).
However, taking into account the total duration of the mus-
cular contraction duringa1RMhalf-squat, an extremely
rapid degradation of PCr should be expected to occur during
this type of exercise. Thus, in the present study, the average
measured duration of the dynamic phase during the 1 RM
half-squat test was 1.56 s. Assuming a previous isometric
phase duration of 0.5–1 s, this would mean a total muscular
contraction time of 2.0–2.5 s duringa1RMhalf-squat test.
Greenhaff et al. (13) estimated that the peak rates of ATP
production from PCr begins to decline after only 1.3 s of
contraction during isometric and dynamic maximal muscu-
lar actions in humans. After this peak, there is a progressive
decline in ATP provision and a parallel decline in force
production and power output (13). This means that during a
1 RM half-squat, PCr contributes a large fraction of the total
ATP supply and there is an extremely rapid rates of ATP
production and PCr degradation. It may be suggested that
raising the total Cr concentration after Cr supplementation
will not only increase the amount of PCr initially available
for contraction but might also retard the moment when the
peak rates of ATP production from PCr begin to decline.
This delay might substantially enhance the rate of ATP
synthesis and the amount of power generated during the few
first seconds of duration of a very power-demanding exer-
cise as such 1 RM. Therefore, an improved power-generat-
ing capacity during the few first seconds of exercise after
short-term Cr loading could explain the increase in 1RM
half-squat exercise. Another plausible explanation for this
initial improvement in 1RM half-squat could be the de-
creased intensity and duration of the handball and strength/
endurance training sessions that took place during the week
of the study. Finally, the protocol for determination of 1RM
dynamic strength could have some influence on the ob-
served enhancement of 1 RM after Cr supplementation
(3,19). Thus, 1 RM dynamic strength is determined by 3–6
progressive contraction efforts to establish the maximum
separated by only 2-min rest. It is likely that the increased
rate of PCr replenishment (between efforts) found during
recovery after Cr supplementation (13) would allow for
higher muscle strength levels during the subsequent bout of
exercise, translating into improved 1 RM half-squat (3,38).
Cr supplementation differentially affected improvements
in upper- and lower-extremity strength because 1RM bench
press remained unaltered in both the placebo and creatine
group, whereas creatine induced enhancement in 1RM half-
squat. In addition, Cr supplementation significantly im-
proved the average power output during both sets of half-
squat but only improved the average power output during
the second set of bench-press exercises. Differences in max-
imal strength and repeated bouts of submaximal muscle
contractions between upper- and lower-extremity muscles
have been already observed after short-term Cr loading in
isometric-type contractions (35). The greater ability of Cr to
enhance measures of strength and power in activities
FIGURE 4—Countermovement vertical jump values (CMJ) at rest, at
the end of the first set of 10 repetitions of the half-squat (PostR10), and
at the end of the second set (repetitions to fatigue) of the half-squat
(PostR
max
) in the placebo group (A) and in the creatine group (B), pre-
and post-supplementation. * Denotes a significant difference between
pre- and post-supplementation (P<0.05) Values are means ⴞSD.
Significance are as described in Figure 1.
CREATINE AND REPETITIVE EXERCISE PERFORMANCE Medicine & Science in Sports & Exercise姞
339

involving larger muscle groups might be explained by dif-
ferences in the pattern of quantity and/or intensity of daily
physical use in normal life and handball training. The quad-
riceps muscle, owing to its weight-bearing role during ha-
bitual activity and handball training, would more likely be
exercised than the upper-body muscles, which are used less
frequently. It has been shown that exercise may provide an
additive effect relative to muscle Cr uptake during Cr sup-
plementation (14), probably related to a higher uptake of Cr
in exercised muscles. Therefore, the greater gains in
strength and power made by the legs after Cr supplemen-
tation might be partly related to an enhanced Cr loading in
the leg muscles due to a higher degree of solicitation during
daily physical activity and handball training. Nevertheless,
the potential role of creatine supplementation and phosph-
agen metabolism in mediating acute increases in maximal
strength of upper- and lower-extremity muscle performance
needs further attention.
Although Cr supplementation induced an increase in
body mass, single vertical jump performance at resting
condition was not impaired in the Cr group. These results
agree with other studies performed with male subjects (27)
and suggest that short-term Cr loading does not appear to
significantly affect a single high-intensity explosive perfor-
mance, which seems to be rather limited by the intrinsic
limitations of the contractile proteins (i.e., rate of calcium
acto-myosin ATPase activity) or by motor unit recruitment
(28). However, the Cr group was able to maintain a signif-
icant higher postsupplementation jumping performance
level after completion of the first set of 10 repetitions with
the 70% of 1 RM half-squat, whereas the placebo group did
not show any significant change after the intervention pe-
riod. A similar finding has been reported by Mujika and
coworkers (27), who observed an attenuated decline in
jumping performance after a maximal intermittent soccer-
specific test (40 ⫻15-s bouts of high-intensity running
interspersed by 10-s bouts of low-intensity running) after 5 d
of creatine loading (20 g·d
⫺1
). Greenhaff et al. (11) found
that after Cr supplementation there is an increased velocity
of PCr resynthesis during recovery from intense muscle
contraction. Bogdanis et al. (7) found that the resynthesis of
muscle PCr and the restoration of peak power output pro-
ceeded in parallel after a 30-s cycle sprint. Taking these
observations together, it can be suggested that the attenuated
decline in jumping ability observed after the first set of 10
repetitions with the 70% of 1RM half-squat in the Cr group
could be related to a facilitated generation of intramuscular
PCr occurring during recovery, probably as a consequence
of an increase in Cr availability.
Creatine supplementation significantly improved perfor-
mance during the first 5 meters of repeated bouts of 15-m
sprint runs. These results confirm previous findings ob-
served in our laboratory with highly trained soccer players
(27) and others with handball players (1) and suggest that Cr
FIGURE 5—Five- and 15-m run times during the repeated sprint test before and after the creatine or placebo supplementations period. * Denotes
a significant difference between pre- and post-supplementation (P<0.05). Values are means ⴞSD. Significance are as described in Figure 1.
340
Official Journal of the American College of Sports Medicine http://www.acsm-msse.org

supplementation provides a potential benefit in energy pro-
vision during very short-term, high-intensity exercise, espe-
cially when performed in repeated succession. However,
these results differ from other studies in which no ergogenic
effects (22,31,32) or mixed effects (29,34) were found on
sprint running performance after Cr supplementation. The
conflicting results between studies regarding the effects of
Cr supplementation on sprint running performance could be
attributed to differences in the amount of repetitions and
frames or distances tested. Indeed, the studies that have
found no effects or mixed effects of acute Cr loading tested
sprint running performance with only a single bout
(22,29,34) or with repeated bouts of distances greater than
15 m (31,32). As mentioned previously, a clearer improve-
ment in sprint performance after Cr loading should be ex-
pected during repeated short supramaximal exercise of 1- to
2-s duration because: 1) during this time frame, PCr gener-
ates the highest peak rates of ATP production (13); 2) PCr
availability is critical for power generation during the initial
seconds of exercise (6); and 3) Cr loading may increase the
rate of PCr resynthesis during recovery periods after muscle
contractions (11,13). When only one bout of sprint running
is performed and/or the time frame of each bout is higher
than 1–2 s, the effects of Cr loading should be less pro-
nounced and could be hindered by the absence of effect of
PCr resynthesis during recovery periods (single bout), a
lower contribution of PCr to ATP provision and the increase
in body mass that normally occurs with Cr loading. From a
practical point of view, it may be interesting to point out that
the improvement in repeated sprint runs and in body mass
found in the present study after Cr supplementation may be
advantageous for very high contact sports, such as handball.
Most of the studies focused on endurance exercise do not
support the ergogenic effect of acute Cr supplementation or
even may argue an ergolytic effect on it (4,9,27,33), partly
due to creatine-induced increases in body mass with conse-
quently higher absolute rate of O
2
consumption, as well as
to the expected smallness role that the PCr system plays in
muscle function during exercise of this nature (3,4,9,27,33).
The theoretical mechanism for supporting the possible er-
gogenic effects of Cr supplementation on submaximal ex-
ercise performance relies on the role of cytosolic Cr as an
acceptor of mitochondrial ATP (6,26). In the present study,
during the maximal multistage discontinuous incremental
running test, lower blood lactate concentrations were ob-
served in the placebo group at 10 km·h
⫺1
and 12 km·h
⫺1
after the administration period, whereas no changes were
observed in the Cr group. It has been suggested that a
decrease in blood lactate concentrations during submaximal
exercise as a result of training is associated with improved
endurance performance (40). This decrease in blood lactate
concentration in the placebo group is somewhat surprising
and difficult to explain, but it could be related to a possible
tapering effect caused by the training reduction and the
absence of official handball games that took place during the
intervention week of the study, which took place in the
middle of a very demanding competitive season. On this
assumption, it might be hypothesized that the absence of
decrease in blood lactate observed in the Cr group during
submaximal running suggests that Cr supplementation in-
terfered with the development of endurance running ob-
served in the placebo group during the administration pe-
riod. However, the time to exhaustion observed during the
endurance running test does not support a negative effect of
Cr intake on endurance running because no differences in
time to exhaustion were observed in either group after the
supplementation period. Taking the submaximal and maxi-
mal responses observed during the maximal multistage dis-
continuous incremental running test together, it can be sug-
gested that Cr supplementation did not result in any
improvement in performance of endurance running exercise.
Further research, including measuring performance during
different types of aerobic exercise and a higher number
of subjects are needed to evaluate the importance of Cr
supplementation during endurance running exercise in
trained subjects.
Cr supplementation led in the present study to an average
increase of 0.6 kg in body mass, whereas it remained unal-
tered in the placebo group. With few exceptions, the ma-
jority of studies have reported increases in body mass of
0.5–3.0 kg after short-term Cr supplementation
(4,24,27,33,37). A possible mechanism underlying short-
term Cr-induced increase in body mass are increases in
water retention in the intramuscular space (16) as a result of
FIGURE 6—Blood lactate concentrations during a maximal discon-
tinuous incremental running test in absolute values before and after
the creatine or placebo supplementation period (*P<0.05; **P<0.01
between pre- and post-supplementation). Values are means ⴞSD.
Significance are as described in Figure 1.
CREATINE AND REPETITIVE EXERCISE PERFORMANCE Medicine & Science in Sports & Exercise姞
341

the cellular transport of Cr with Na
⫹
(16). Some researches
also suggests that the increased cellular hydration induced
by short-term Cr supplementation might increase fat-free
mass as a result of an enhanced myofibrillar protein syn-
thesis or decreased protein degradation (4,37,38). However,
the muscle enlargement induced by Cr supplementation
seems to be more plausible in longer Cr-loading periods
combined with strength-training programs (8,39).
Urinary creatinine excretion was significantly greater af-
ter5dofCrsupplementation when compared with placebo
ingestion. Several studies have demonstrated that short-term
Cr administration led to a significant increase in urinary
creatinine excretion (16), although other studies did not find
differences in creatinine elimination after Cr loading (24).
The low amounts of Cr administered (10 g·d
⫺1
instead of 20
g·d
⫺1
) (26) and the low number of subjects used (N⫽5)
(31) in the studies that did not demonstrate increases in
urinary creatinine excretion may account for this discrep-
ancy. Earlier studies demonstrated that there is no increase
in urinary creatinine excretion until a significant amount of
the administered Cr has been retained (5). Consequently, in
the present study although muscular creatine (total muscle
creatine and PCr) was not directly measured, the creatine-
induced increases in urinary creatinine excretion and body
mass observed after Cr loading indirectly suggests that
Cr supplementation was effective in raising whole-body
Cr stores.
In summary, the present results indicate that short-term
Cr supplementation significantly improved lower-body
maximal strength, maximal repetitive high-power exercise
bouts, and total repetitions performed to fatigue during two
sets of bench-press and half-squat actions in highly trained
handball players. Creatine-supplemented handball players
showed improved performance during the first 5 m of re-
peated bouts of 15-m sprint runs and attenuated decline in
jumping ability after submaximal repetitive high-power-
output half-squat exercise bout. Furthermore, the results
show that Cr supplementation did not result in any improve-
ment in performance of endurance running exercise.
This study was supported in part by a grant from the Instituto
Navarro de Deporte y Juventud (Gobierno de Navarra, Spain).
This article was awarded with the 2001 third prize of the National
Research Sport Medicine award by the University of Oviedo, Spain.
We would like to thank a very dedicated group of subjects and
their coach who made this project possible; Alfredo Zun˜ iga, Alazne
Anto´ n, Maite Ruesta, Miriam Garrue´ s, and Mikel Juaniz for their
excellent technical assistance; and Megaplus creatine (Artesanı´a
Agrı´cola, Barcelona) for providing the creatine monohydrate sup-
plement.
Address for correspondence: Dr. Mikel Izquierdo, Centro de In-
vestigacio´ n y Medicina del Deporte de Navarra, Gobierno de Na-
varra, C/Paulino Caballero, 13, 31002 Pamplona (Navarra), Spain;
E-mail: mizquierdo@jet.es.
REFERENCES
1. AASERUND, R., P. GRAMVIK,S.R.OLSEN, and J. JENSEN. Creatine
supplementation delays onset of fatigue during repeated bouts of
sprint running. Scand. J. Med. Sci. Sports. 8:247–251, 1998.
2. ALEXANDER, M. J., and S. L. BORESKIE. An analysis of fitness and
time-motion characteristics of handball. Am. J. Sports Med. 1:76–
82, 1989.
3. THE AMERICAN COLLEGE OF SPORTS MEDICINE. The physiological
and health effects of oral creatine supplementation. Med. Sci.
Sports Exerc. 32:706–717, 2000.
4. BALSOM P. D., S. D. R. HARRIDGE,K.So¨DERLUND, and B. EKBLOM.
Creatine supplementation per se does not enhance endurance ex-
ercise performance. Acta Physiol. Scand. 149:521–523, 1993.
5. BENEDICT, S. R., and E. OSTERGERG. The metabolism of creatine.
J. Biol. Chem. 56:229–230, 1923.
6. BESSMAN, S. P., and C. L. CARPENTER. The creatine-creatine phos-
phate energy shuttle. Annu. Rev. Med. 54:831–862, 1985.
7. BOGDANIS, G. C., M. E. NEVILL,L.H.BOOBIS, and A. M. NEVILL.
Recovery of power output and muscle metabolites following 30 s
of maximal sprint cycling in man. J. Physiol. 482:467–480, 1995.
8. EARNEST, C. P., P. G. SNELL,A.L.RODRIGUEZ,A.L.ALMADA, and
K. MITTLEMAN. The effect of creatine monohydrate ingestion on
anaerobic power indices, muscular strength and body composition.
Acta Physiol. Scand. 153:207–209, 1995.
9. ENGELHARDT, M., G. NEUMANN,A.BERBALK, and I. REUTER. Cre-
atine supplementation in endurance sports. Med. Sci. Sports Exerc.
30:1123–1129, 1998.
10. GILLIAM, J. D., C. HOHZONRN,D.MARTIN, and M. H. TRIMBLE.
Effect of oral creatine supplementation on isokinetic torque pro-
duction. Med. Sci. Sports Exerc. 32:993–996, 2000.
11. GREENHAFF, P. L., A. CASEY,A.H.SHORT,R.HARRIS,K.SODER-
LUND, and E. HULTMAN. Influence of oral creatine supplementation
on muscle torque during repeated bouts of maximal voluntary
exercise in man. Clin. Sci. 84:565–571, 1993.
12. GREENHAFF, P. L., K. BODIN,K.SODERLUND, and E. HULTMAN.
Effect of oral creatine supplementation on skeletal muscle phos-
phocreatine resynthesis. Am. J. Physiol. 2 66:E725–E730, 1994.
13. GREENHAFF, P. L., C. BODIN,A.CASEY, et al. Dietary creatine
supplementation and fatigue during high-intensity exercise in hu-
mans. In: Biochemistry of Exercise, Vol IX, R. J. Maughan and
S. M. Shireffs (Eds.). Champaign, IL: Human Kinetics, 1996, pp.
219–242.
14. HARRIS, R. C., K. So¨DERLUND, and E. HULTMAN. Elevation of
creatine in resting and exercised muscle on normal subjects by
creatine supplementation. Clin. Sci. 83:367–374, 1992.
15. HIRVONEN, J., S. REHUNEN,H.RUSKO, and M. HARKONEN. Break-
down of high-energy phosphate compounds and lactate accumu-
lation during short supramaximal exercise. Eur. J. Appl. Physiol.
56:253–259, 1987.
16. HULTMAN, E. K., K. So¨DERLUND,J.A.TIMMONS,G.CEBERLAND, and
P. L. GREENHAFF. Muscle creatine loading in men. J. Appl. Physiol.
81:232–237, 1996.
17. JACKSON, A. G., and M. L. POLLOCK. Prediction accuracy of body
density, lean body weight and total body volume equations. Med.
Sci. Sports. Exerc. 9:197–201, 1977.
18. KELLY, V. G., and D. G. JENKINS. Effect of oral creatine supple-
mentation on near-maximal strength and repeated sets of high-
intensity bench press exercise. J. Strength Cond. Res. 12:109–115,
1998.
19. KRAEMER, W. J., and J. S. VOLEK. Creatine supplementation: its
role in human performance. Clin. Sports Med. 18:651–661, 1999.
20. KREIS, R., M. KAMBER,M.KOSTER, et al. Creatine supplementation.
Part II: in vivo magnetic resonance spectroscopy. Med. Sci. Sports
Exerc. 31:1770–1777, 1999.
21. KREIDER, R. B., M. FERREIRA,M.WILSON, et al. Effects of creatine
supplementation on body composition, strength and sprint perfor-
mance. Med. Sci. Sports Exerc. 30:73–82, 1998.
22. LEFAVI, R. G., J. L. MCMILLAN,P.J.KAHN,J.F.CROSBY,R.F.
DIGIOACCHINO, and J. A. STREATER. Effects of creatine monohy-
drate on performance of collegiate baseball and basketball players.
J. Strength Cond. Res. 12:275–279, 1998.
23. MACDOUGALL, J. D., G. R. WARD,D.G.SALE, and J. R. SUTTON. Bio-
chemical adaptation of human skeletal muscle to heavy resistance train-
ing and immobilization. J. Appl. Physiol. 43:700–703, 1977.
342
Official Journal of the American College of Sports Medicine http://www.acsm-msse.org

24. MAGANARIS, C. N., and R. J. MAUGHAN. Creatine supplementation
enhances muscle strength and endurance capacity in resistance-
trained men. Acta Physiol. Scand. 17:560–567, 1998.
25. MCKENNA, M. J., J. MORTON,S.E.SELIG, and R. J. SNOW. Creatine
supplementation increases muscle total creatine but not maximal
intermittent exercise performance. J. Appl. Physiol. 87:2244–
2252, 1999.
26. MEYER, R. A., H. L. SWEENEY, and M. J. KUSHMERICK. A simple
analysis of the “phosphocreatine shuttle.”Am. J. Physiol. 246:
C365–C377, 1984.
27. MUJIKA, I., S. PADILLA,J.IB´
A˜
NEZ,M.IZQUIERDO, and E. M. GOR-
OSTIAGA. Creatine supplementation and sprint performance in soc-
cer players. Med. Sci. Sports Exerc. 32:518–525, 2000.
28. NIELSEN, O. B., and K. OVERGAARD. Ion gradients and contractility
in skeletal muscle: the role of active Na
⫹
,K
⫹
transport. Acta
Physiol. Scand. 156:247–256, 1998.
29. NOONAN, D., K. BERG,R.W.LATIN,J.C.WAGNER, and K. REIMERS.
Effects of varying dosages of oral creatine relative to fat free body
mass on strength and body composition. J. Strength Cond. Res.
12:104–108, 1998.
30. ODLAND, M. L., J. D. MACDOUGALL,M.A.TARNOPOLSKY,A.ELOR-
RIAGA, and A. BORGMANN. Effect of oral creatine supplementation
on muscle [Pcr] and short-term maximum power output. Med. Sci.
Sports Exerc. 29:216–219, 1997.
31. REDONDO, D. R., E. A. DOWLING,B.L.GRAHAM,A.L.ALMADA, and
M. H. WILLIAMS. The effect of oral creatine monohydrate supplemen-
tation on running velocity. Int. J. Sports Nutr. 6:213–221, 1996.
32. SMART, N. A., S. G. MCKENZIE,L.M.NIX, et al. Creatine supple-
mentation does not improve repeated sprint performance in soccer
players. Med. Sci. Sports Exerc. 30:S140, 1998.
33. STROUD, M. A., D. HOLLIMAN,D.BELL,A.L.GREEN,I.A.MC-
DONALD, and P. L. GREENHAFF. Effect of oral creatine supplemen-
tation on gas exchange and blood lactate accumulation during
steady-state incremental treadmill exercise and recovery in man.
Clin. Sci. 87:707–710, 1994.
34. STOUT, J. R., J. ECHERSON,D.NOONAN,G.MOORE, and D. CULLEN.
Effects of creatine supplementation on exercise performance and
fat-free weight in football players during training. Nutr. Res.
19:217–225, 1999.
35. URBANSKI R. L., S. F. LOY,W.J.VINCENT, and B. B. YASPELKIS III.
Creatine supplementation differentially affects maximal isometric
strength and time to fatigue in large and small muscle groups. Int.
J. Sports Nutr. 9:136–45, 1999.
36. VANDENBERGHE, K., N. GILLIS,M.VAN LEEMPUTTE,P.VAN HECKE,
F. VANSTAPEL, and P. HESPEL. Caffeine counteracts the ergogenic
action of muscle creatine loading. J. Appl. Physiol. 80:452–7,
1996.
37. VOLEK, J. S., M. BOETES,J.A.BUSH,M.PUTUKIAN,W.J.SEBAS-
TIANELLI, and W. J. KRAEMER. Response of testosterone and cortisol
concentrations to high-intensity resistance exercise following cre-
atine supplementation. J. Strength Cond. Res. 11:182–7, 1997.
38. VOLEK, J. S., W. J. KRAEMER,J.A.BUSH, et al. Creatine supple-
mentation enhances muscular performance during high-intensity
resistance exercise. J. Am. Diet. Assoc. 97:765–770, 1997.
39. VOLEK, J. S., N. D. DUNCAN,S.A.MAZZETTI, et al. Performance
and muscle fiber adaptations to creatine supplementation and
heavy resistance training. Med. Sci. Sports Exerc. 31:1147–56,
1999.
40. WELTMAN,A.The Blood Lactate Response to Exercise. Cham-
paign, IL: Human Kinetics, 1995, pp. 1–115.
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