Journal of Strength and Conditioning Research, 1999, 13(4), 394–399
q 1999 National Strength & Conditioning Association
Creatine Supplementation Does Not Increase
Peak Power Production and Work Capacity
During Repetitive Wingate Testing in Women
ASHLEIGH LEDFORD
AND
JOHN DAVID BRANCH
Human Performance Laboratory, Wellness Institute and Research Center, and Department of Exercise Science,
Physical Education, and Recreation, Old Dominion University, Norfolk, Virginia 23529.
ABSTRACT
The effect of creatine monohydrate (CM) supplementation on
performance of high-intensity, short-duration tasks has been
studied extensively in men, but few studies have investigated
this issue in women. To test the hypothesis that CM improves Wingate test (WT) peak power production and work
capacity in women, 9 well-trained subjects (baseline age
mean 6 SD 5 27 6 6 years; body mass 5 56.9 6 5.7 kg;
peak power 5 538 6 105 W; work capacity 5 12.27 6 1.20
kJ) received, in a double-blind manner with counterbalanced
treatment order, 2 supplementation regimens (20 g·d21 for 5
days) of both CM and Polycose placebo (PL). Both CM and
PL were separated by a 95 6 3-day washout period. Immediately following each supplementation period, subjects completed 3 WTs, interspersed with a 5-minute rest interval. No
significant treatment (p 5 0.30) or treatment-by-test interaction effects (p 5 0.39) were observed in WT peak power
production (CM mean 6 SE 5 540 6 30, 484 6 23, 435 6
19 W vs. PL 5 522 6 30, 481 6 22, 403 6 32 W). The WT
work capacity was also unchanged by CM supplementation
(CM mean 6 SE 5 12.39 6 0.67, 10.60 6 0.50, 9.56 6 0.59
vs. PL 5 12.09 6 0.32, 10.60 6 0.54, 9.39 6 0.67 kJ) with no
treatment (p 5 0.76) or treatment-by-test interaction effects
(p 5 0.66). The practical application of this study is that 5
days of CM supplementation did not increase WT peak power production and work capacity in women.
Key Words: ergogenic, phosphocreatine, glycolysis, ergometer, anaerobic
Reference Data: Ledford, A., and J.D. Branch. Creatine
supplementation does not increase peak power production and work capacity during repetitive Wingate
testing in women. J. Strength Cond. Res. 13(4):394–399.
1999.
Introduction
C
reatine, an endogenous nitrogenous amine capable
of rapid and reversible phosphorylation, is an important source of phosphate for anaerobic adenosine
triphosphate (ATP) synthesis by the ATP-phosphocre394
atine (PCr) energy system. As early as the 1920s, it was
hypothesized that an increase in free creatine through
exogenous supplementation could result in rapid replenishment of PCr and ATP synthesis during highintensity, short-duration activity (9). Since 1990, the ergogenicity of creatine supplementation has been most
extensively investigated in single-bout and repetitive
high-intensity performance tasks of #30 seconds (i.e.,
tasks that rely primarily on the ATP-PCr system) and
has been the subject of several recent reviews (2, 16,
17, 26, 40). Many studies have reported enhanced performance in laboratory tasks, such as cycle ergometry
(1, 3, 6, 8, 11, 12, 29, 33), isotonic force production (12,
39), and isokinetic (18, 36) force production following
creatine supplementation. Other studies, however, reported no improvement in cycle ergometer tasks #30
seconds (4, 10, 11, 28) and 25-m swim (7, 27) and 60m sprint (30) performance tasks following creatine
supplementation, indicating that this issue remains
equivocal.
The literature is replete with studies of enhanced
performance in various tasks by men following creatine supplementation, but there are few investigations
involving women. Although long-term (10-week) creatine supplementation combined with resistance training has recently been reported to enhance muscle
strength in women (38), no improvement in upperbody isokinetic torque (20, 37, 38) or isotonic strength
(20) has been observed in women following short-term
(#7 days) supplementation. Furthermore, the effect of
creatine supplementation on lower-body anaerobic
power and work capacity as measured by cycle ergometer testing has been studied in men (6, 8, 12, 28) but
not in women. Therefore, the purpose of this study
was to investigate the effect of creatine supplementation on power production and work capacity during
repetitive Wingate cycle ergometer tests in physically
active women using a double-blind, placebo-control,
crossover design.
Creatine Supplementation in Women 395
Methods
Subjects
Subjects (N 5 10) were physically active women who
were exercise science college students (mean 6 SD, age
5 27 6 6 years, body mass 5 56.6 6 5.8 kg) who
denied currently taking any nutritional supplement.
Subjects were instructed to maintain both normal nutritional intake and level of physical activity for the
entire study. Before participation, subjects were appraised of potential risks and provided informed consent in accordance with the Institutional Review Board
of Old Dominion University.
Testing Protocol
The Wingate test of anaerobic power production and
work capacity (5) was administered using a Monark
818E cycle ergometer equipped with a digital revolution counter and a resistance pendulum. Before each
test, revolution counter calibration was confirmed by
observing the digital display in response to incremental pedal revolutions (i.e., right leg extension to next
right leg extension 5 1 unit). The resistance pendulum
was calibrated at both 39.2 N (using a 4.0-kg mass)
and 0 N of force. Before testing, subjects completed a
standardized 5-minute warm-up (50 rev·min21 pedal
rate against 33% of the resistance force to be used in
the test), which also included 4 maximal ‘‘sprint’’
bouts lasting 5 seconds. Subjects then rested passively
for 2 minutes, followed by static stretching (10 seconds
each) of hamstring, hip flexor, quadricep, and calf
muscles. Immediately preceding testing, subjects pedaled for 10 seconds against 33% of the test resistance
force and were then instructed to achieve a maximal
pedal revolution rate. The pendulum was quickly adjusted to apply a resistance force to the ergometer flywheel, which was calculated to the nearest 0.25 kg as
follows:
Ergometer Resistance Mass (kg)
5 Body Mass (kg) · 0.075
(1)
Ergometer Resistance Force (N)
5 Resistance (kg) 4 0.102
(1A)
When the resistance was set, the test commenced (T0)
with simultaneous resetting of the revolution counter
to 0. Subjects were verbally encouraged to maintain
the maximal possible pedal rate for the duration of the
30-second test. Cumulative revolutions were recorded
every 5 seconds (i.e., T5, T10, T15, T20, T25, T30). Power
production for each 5-second interval was calculated
in watts as follows:
Power (W) 5 Resistance (kg) · (6 m·rev21 )
· (rev·min21 rate) 4 6.12
(2)
Peak power production was the highest rate of power
production during any 5-second interval and was ob-
served in the first or second 5-second interval (i.e.,
from T0–T5 or from T6–T10). Work capacity was calculated in kilojoules as follows:
Work (kJ) 5 Resistance (kg) · (6 m·rev21 )
· (total rev) · 9.8 4 1000
(3)
Design
The study commenced in the summer of 1997. Following familiarization with the test protocol, subjects
were administered a minimum of 2 Wingate tests separated by at least 3 days for measurement of baseline
peak power production and work capacity. For statistical purposes, baseline peak power production and
work capacity were reported as the mean of the best
2 tests with a reliability coefficient of variation of #5%
(mean 5 2.3%). The test-retest correlation coefficient
(r 5 0.91) for baseline work capacity was similar to
previously reported data on Wingate test reliability (5).
Subjects were then matched according to baseline values for age, body mass, peak power, and work capacity. In a double-blind, counterbalanced treatment order
manner, subjects in each pair were randomly assigned
to creatine monohydrate (CM, Universal Labs, New
Brunswick, NJ) or glucose polymer placebo (PL, Polycose) supplementation regimens (20 g·d21 for 5
days). The CM or PL was provided to subjects in
weighed (;120 g) unlabeled vials. Subjects refrained
from ingesting caffeine, which has been reported to
eliminate the ergogenic effect of creatine supplementation (36). Since it has also been reported that creatine
uptake is augmented when combined with carbohydrate (15), subjects were instructed to ingest supplements (4 separate doses of ;5 g [i.e., ;1 heaping teaspoon]) dissolved in ;8 oz of orange juice. Vials were
returned to confirm compliance with the supplementation regimen. On the day following completion of the
initial supplementation (day 6), subjects were administered 3 Wingate tests interspersed by a 5-minute rest
interval, during which peak power and work capacity
were measured. A 3-month (95 6 3 day) washout period followed the initial supplementation and testing.
Subjects were administered a minimum of 2 postwashout Wingate tests for the purpose of comparing baseline and postwashout peak power and work capacity.
The other supplementation regimen was then administered in a double-blind, counterbalanced treatment
order manner, followed by repetitive Wingate testing.
For each subject, data were collected at approximately
the same time of day throughout the study to minimize any circadian effect on performance.
Statistical Analyses
The effects of creatine supplementation on peak power
production, work capacity, and body mass were analyzed by repeated-measures analysis of variance using
SAS version 6.09 PROC GLM (32). The criterion for
396 Ledford and Branch
Table 1. Characteristics of the subjects at baseline (BL)
and following the washout (WO) period (mean† 6 SE).
Variable
Age (yr)
Body mass (kg)
Peak power (W)
Work capacity (kJ)
Group 1‡
BL
WO
BL
WO
BL*
WO
26
54.4
54.3
526
540
12.24
10.94
6
6
6
6
6
6
6
4
2.9
2.7
77
53
0.86
0.84
Group 2§
28
58.9
58.0
547
600
12.30
11.69
6
6
6
6
6
6
6
7
2.8
2.9
28
39
0.35
0.39
* Time main effect, BL work capacity . WO work capacity
(p 5 0.0004).
† Peak power and work capacity values are the mean for
the best 2 tests at BL and post-WO, respectively.
‡ Placebo → creatine monohydrate, n 5 4.
§ Creatine monohydrate → placebo, n 5 5.
significant treatment (CM vs. PL), test (postsupplement Wingate test 1 vs. test 2 vs. test 3), and treatment-by-test interaction effects was a 5 0.05, with a
Bonferroni adjustment for post hoc comparisons.
Results
Subject Characteristics at Baseline and Following
Washout
One subject became ill during repetitive Wingate testing following both supplementation regimens and
failed to complete the testing protocol. The following
results are based on the remaining (N 5 9) subjects.
Baseline and postwashout values for age, body mass,
power, and work capacity are presented in Table 1.
According to study design, there were no significant
differences between groups 1 (PL → CM) and 2 (CM
→ PL) at baseline or following washout. For all subjects, there were no differences in body mass (p 5 0.66)
or peak power production (p 5 0.54) at baseline compared with postwashout, but work capacity was greater at baseline than at postwashout (p , 0.0004).
Subjects returned empty vials following each supplementation period and reported the ingestion of CM
and PL according to the prescribed regimen. Furthermore, a McNemar x2 test for dependent samples (31)
revealed no association between supplementation regimen and ability to discern the treatment (p 5 0.37),
suggesting that subjects were adequately blinded to
treatments.
Peak Power Production Following CM
Supplementation
The effect of CM on peak power production during
repetitive Wingate testing is presented in Table 2. As
expected, a significant Wingate test main effect was
observed since peak power production declined during repetitive testing following both CM and PL (p ,
0.002). However, CM supplementation did not improve peak power production compared with PL (p 5
0.30). Furthermore, the interaction between treatment
and test was not significant (p 5 0.52), suggesting that
the decline in peak power production during repetitive Wingate testing was not attenuated by CM supplementation.
Work Capacity Following CM Supplementation
The significant Wingate test main effect (p , 0.0005)
observed following both CM and PL documented the
expected decline in work capacity during repetitive
bouts. Work capacity was not changed following CM
compared with PL (p 5 0.76), nor was the decline in
work performed in repetitive bouts attenuated by CM
supplementation (p 5 0.76 for test-by-treatment interaction).
Effect of CM Supplementation on Body Mass
Body mass was unchanged (p 5 0.56) across 6 trials
(mean 6 SE; pre-PL1 5 56.8 6 1.8; pre-PL2 5 56.7 6
1.8; post-PL 5 56.4 6 1.8; pre-CM1 5 57.0 6 1.8; preCM2 5 56.8 6 1.9; post-CM 5 56.1 6 1.8 kg).
Discussion
In recent years, the efficacy of CM as an ergogenic aid
has received considerable but not unanimous research
support. As a result, the issue remains somewhat
equivocal. In addition, disproportionate research attention has been placed on men. Examination of
mixed-sex studies (7, 18, 29, 30) and abstracts (22, 23,
24, 41) of creatine ergogenicity reveals most subjects
to be men, with only 2 of these studies (18, 29) reporting an ergogenic effect. Few crossover designs exist in the literature (14, 25, 27, 36). To our knowledge,
the present study is the only double-blind, crossover
design of creatine supplementation in women. The key
Table 2. Effect of creatine supplementation on peak power output and work capacity during repetitive Wingate tests (mean
6 SE).
Variable
Peak power (W)
Work capacity (kJ)
Treatment
PL
CR
PL
CR
Test 1
523
540
12.09
12.39
6
6
6
6
30
30
0.32
0.67
Test 2
481
484
10.60
10.60
6
6
6
6
22
23
0.54
0.50
Test 3
403
435
9.39
9.56
6
6
6
6
32
19
0.67
0.59
Creatine Supplementation in Women 397
finding of our study was that creatine supplementation
(20 g·d21 for 5 days) did not increase Wingate test peak
power production or work capacity in physically active women. These results are in agreement with previous reports of no improvement in isotonic strength
or endurance (20), middle distance interval running
(34), or isokinetic torque production (20, 37, 38) in
women following short-term (#7 days) creatine supplementation. This small but unanimous group of null
findings suggests that short-term supplementation
may not be effective in active women.
The ergogenicity of long-term creatine supplementation in women has been the focus of 2 studies (35,
38). Thompson et al. (35) reported that 42 days of creatine supplementation (2 g·d21) failed to improve 100and 400-m swim performance. Muscle PCr, PCr:b-ATP
ratio, and adenosine diphosphate, measured using
phosphorus-31 nuclear magnetic resonance spectroscopy and near-infrared spectroscopy at rest and during exercise (plantar flexion) both before and after
supplementation remained unchanged. In contrast,
Vandenberghe et al. (38) reported that ‘‘high-dose’’
creatine supplementation (20 g·d21 for 4 days), followed by 10 weeks of ‘‘low-dose’’ creatine supplementation (5 g·d21), combined with resistance training significantly increased muscle strength and isokinetic
arm torque compared with a training group that ingested a placebo. Creatine supplementation also increased muscle PCr, PCr:b-ATP ratio, and fat-free
mass. One possible explanation for these discordant
findings is the 5-fold difference in total creatine ingested.
There appears to be better research support for improvement in high-intensity, short-duration (#30 seconds) work performance following short-term creatine
supplementation in men compared with women,
which begs the elucidation of a possible explanatory
mechanism. In a sex comparison of muscle composition, Forsberg et al. (13) reported a 10% greater concentration of total muscle creatine (TCr) in women (145
6 10 mmol·kg21 dry mass) compared with men (132
6 10 mmol·kg21 dry mass). It is plausible that women,
with higher endogenous TCr than men, are less responsive to creatine supplementation. Although this
explanation is consistent with our finding, muscle TCr
was not measured in the present study. Therefore, further commentary would be speculative.
Considerable interindividual variation appears to
exist in response to creatine uptake in men. It has been
reported that human muscle has an upper TCr of 150–
160 mmol·kg21 dry mass (16). Greenhaff et al. (19) reported a 25% increase in muscle TCr in 5 (63%) of 8
men but no increase in the other 3 subjects following
a creatine supplementation regimen similar to that
used in this study (20 g·d21 for 5 days). In their study
(19), increased muscle TCr was observed in individuals with low-normal endogenous TCr levels (;120
mmol·kg21 dry mass) following creatine supplementation, whereas subjects with higher endogenous TCr
were somewhat less responsive. It has been suggested
by Casey et al. (8) that enhanced performance may be
associated with creatine uptake by type IIb (fast glycolytic) fibers. Interindividual differences in muscle fiber types may affect response to supplementation,
with a lower muscle creatine uptake observed in individuals with a greater percentage of type I (slow
oxidative) fibers. Although the subjects in the present
study participated primarily in aerobic activities, such
as swimming, bicycling, and running, the muscle fiber
distribution of these subjects is unknown since fiber
typing was not included in our methods.
Increases in body mass of 0.7–2.0 kg have been reported in men following short-term (20–25 g·d21 for 5–
7 days) creatine supplementation (1, 3, 11, 12, 15, 19,
39). According to Hultman et al., urinary volume is
decreased during short-term supplementation (21), a
finding that suggests that water retention may explain
the early increase in body mass. Our finding of no
change in body mass in women following a 20 g·d21
for 5 days supplementation regimen is in accord with
other studies of women athletes (20, 34, 35). However,
Vandenberghe et al. (38) reported a 60% greater increase in fat-free mass following 10 weeks of creatine
supplementation combined with resistance training
compared with a resistance training group that ingested a placebo. A sex effect, if real, may possibly be
explained by the previously discussed sex differences
in baseline TCr and the resulting decreased responsiveness to creatine uptake.
Limitations to the present study include no measurement of muscle TCr, which is essential to investigate sex differences in endogenous TCr, muscle creatine uptake, and effectiveness of creatine supplementation. Although the study was well designed, with
counterbalanced treatment order and a washout period exceeding the 4 weeks required for muscle TCr to
return to baseline (38), the 3-month washout may have
increased the chance of a maturation or history threat
to internal validity. The decreased work capacity following washout compared with baseline was probably
related to the fact that the postwashout treatment was
administered during midsemester examinations, a
time of decreased physical activity for the student subjects. Although the treatment main effect and treatment-by-test interaction did not approach statistical
significance, the sample size was small and the observed statistical power may have been low. Finally,
the Wingate and other 30-second cycling tests have
been used to assess the efficacy of creatine supplementation (6, 8, 12, 28), but work capacity, which requires contribution of ATP by fast glycolysis, is a more
reliable Wingate test measurement than peak power
production, which is more closely linked to the ATPPCr energy system (5).
398 Ledford and Branch
It is recommended that future investigations of this
issue include direct sex comparison of baseline TCr
and subsequent creatine uptake in a design that controls for such possible confounding influences as muscle fiber type distribution and baseline muscle TCr.
Previously reported mixed-sex designs have lacked adequate statistical power to investigate sex as a main
effect.
In summary, 5 days of CM supplementation failed
to increase peak power and work capacity during repetitive Wingate testing in active women. Creatine
supplementation appears to be more effective in men,
and the result of this study is in agreement with the
null findings of other researchers with regard to the
ergogenicity of short-term creatine supplementation in
women. Although a direct sex comparison awaits investigation, it is possible that differences in baseline
muscle TCr between men and women may affect subsequent responsiveness of women to creatine supplementation.
8.
9.
10.
11.
12.
13.
14.
Practical Applications
Creatine monohydrate is an increasingly popular supplement used by many physically active individuals.
Reported outcomes associated with creatine supplementation include increased body mass and enhanced
performance in high-intensity, short-duration tasks.
There is considerable research support for the ergogenicity of creatine in men. However, the results of this
and other studies suggest that short-term creatine supplementation may be less effective in women than
men. A comparative study of creatine uptake and ergogenicity in men and women would help clarify this
issue.
15.
16.
17.
18.
19.
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Acknowledgments
The authors are indebted to the subjects for their efforts; to Karen DeBause and Trent Woodroof for their
technical assistance; and to Universal Laboratories, 3
Terminal Road, New Brunswick, NJ, for providing the
creatine monohydrate.