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44 Volume 38
•
Number 1
•
March 2003
Journal of Athletic Training 2003;38(1):44–50
q by the National Athletic Trainers’ Association, Inc
www.journalofathletictraining.org
Creatine Supplementation Increases
Total Body Water Without Altering
Fluid Distribution
Michael E. Powers*; Brent L. Arnold†; Arthur L. Weltman‡; David H. Perrin§;
Dilawaar Mistry‡; David M. Kahler‡; William Kraemer\; Jeff Volek\
*University of Florida, Gainesville, FL; †Virginia Commonwealth University, Richmond, VA; ‡University of Virginia,
Charlottesville, VA; §University of North Carolina at Greensboro, Greensboro, NC; \University of Connecticut,
Storrs, CT
Michael E. Powers, PhD, ATC, CSCS, contributed to conception and design; acquisition and analysis and interpretation of the
data; and drafting, critical revision, and final approval of the article. Brent L. Arnold, PhD, ATC, contributed to conception and
design; analysis and interpretation of the data; and drafting, critical revision, and final approval of the article. Arthur L.
Weltman, PhD, and David H. Perrin, PhD, ATC, contributed to conception and design and drafting and final approval of the
article. Dilaawar Mistry, MD, ATC, and David M. Kahler, MD, contributed to acquisition of the data and drafting and final
approval of the article. William Kraemer, PhD, contributed to conception and design; analysis and interpretation of the data;
and drafting and final approval of the article. Jeff Volek, PhD, contributed to analysis and interpretation of the data and drafting
and final approval of the article.
Address correspondence to Michael E. Powers, PhD, ATC, CSCS, 144 FL Gym, PO Box 118205, Gainesville, FL 32611-8205.
Address e-mail to mpowers@hhp.ufl.edu.
Objective:
To examine the effects of oral creatine (Cr) mono-
hydrate supplementation on muscle Cr concentration, body
mass, and total body water (TBW), extracellular water (ECW),
and intracellular water (ICW) volumes.
Design and Setting:
After an overnight fast, urinary Cr and
creatinine concentrations, muscle Cr concentration, body mass,
TBW, ECW, and ICW were measured, and subjects were ran-
domly assigned to either a Cr or a placebo (P) group. The Cr
group ingested 25 g/d of Cr for 7 days (loading phase) and 5
g/d for the remaining 21 days (maintenance phase), whereas
the P group ingested a sucrose P using the same protocol. All
the measures were reassessed immediately after the loading
and maintenance phases.
Subjects:
Sixteen men (age 5 22.8 6 3.01 years, height 5
179.8 6 7.1 cm, body mass 5 84.8 6 11.2 kg) and 16 women
(age 5 21.8 6 2.51 years, height 5 163.4 6 5.9 cm, body mass
5 63.6 6 14.0 kg) involved in resistance training volunteered
to participate in this study.
Measurements:
Muscle Cr concentration was determined
from the vastus lateralis muscle using a percutaneous needle-
biopsy technique. Total body water, ECW, and ICW volumes
were assessed using deuterium oxide and sodium bromide di-
lution analyses.
Results:
The Cr group experienced a significant increase in
muscle Cr concentration, body mass, and TBW. The P group
experienced a small but significant increase in TBW only.
Conclusions:
The Cr supplementation protocol was effective
for increasing muscle Cr concentrations, body mass, and TBW;
however, fluid distribution was not changed.
Key Words:
ergogenic aids, hydration, fluid balance, body
mass, body composition
C
reatine (Cr) supplementation continues to be extremely
popular as a potential ergogenic aid among athletes at
all levels. Studies have shown that muscle Cr and phos-
phocreatine can be significantly elevated when a normal diet
is supplemented with Cr.
1–4
The theory behind its use is sim-
ilar to that of carbohydrate loading, because an increased mus-
cle Cr content would conceivably enhance the capacity of the
phosphagen energy system, providing greater resistance to fa-
tigue and improving performance. Anecdotal reports of ergo-
genic value have been supported by scientifically controlled
studies investigating its effects on strength,
5–8
power,
8–11
speed,
12
and fatigue.
4,13,14
However, not all the findings sup-
port ergogenic claims.
3,15,16
Numerous anecdotal reports have associated muscle cramp-
ing, spasm, strains, gastrointestinal distress, kidney dysfunc-
tion, and heat illness with Cr supplementation. At this time,
however, the only side effect directly associated with Cr sup-
plementation is weight gain.
5–8,11,13,16–19
Some of these au-
thors have reported increases in body mass after only a loading
phase of supplementation (20–25 g/d for 5–7 days).
8,11,13,16
Thus, it is likely that the gains are due more to greater water
retention during supplementation than to lean-tissue accretion.
It is conceivable that increased muscle Cr concentrations are
associated with changes in the intracellular osmotic pressure,
resulting in movement of water into the cell, water retention,
and weight gain. When water loss through sweating occurs
from exercise, increased environmental temperatures, or a
combination of both, this intracellular fluid shift may be det-
rimental. For example, the water bound inside the cell may
not be available to the extracellular compartment for thermal
regulation. Therefore, cramping and other heat-related prob-
lems may result from a fluid shift occurring during supple-
Journal of Athletic Training 45
mentation. However, the existence of this Cr-related fluid shift
is speculative because only 1 group
19
to date has reported
changes in fluid distribution after supplementation. It must be
noted that fluid volumes were not measured directly in that
study but were predicted using a bioelectric impedance anal-
ysis. Furthermore, muscle Cr was not assessed, so whether the
changes in fluid distribution were actually associated with an
increased muscle Cr concentration is unknown. Therefore, the
purpose of this study was to investigate the effects of Cr sup-
plementation on muscle Cr concentration and fluid distribution
using a direct measure of fluid volumes.
METHODS
Subjects
Sixteen men (age 5 22.8 6 3.01 years, height 5 179.8 6
7.1 cm, body mass 5 84.8 6 11.2 kg) and 16 women (age 5
21.8 6 2.51 years, height 5 163.4 6 5.9 cm, body mass 5
63.6 6 14.0 kg) who were involved in a total-body resistance
training program for at least 3 days per week were randomly
assigned to either a Cr supplementation group or a placebo
(P) group. We excluded subjects from participation if they had
supplemented their habitual diet with any form of Cr during
the past 60 days; were suffering from any form of kidney,
liver, or endocrine disease or any disorder that might affect
normal cellular levels of Cr or fluid balance (or both); or were
taking any substance classified as a diuretic other than the
caffeine found in their habitual diet. We also excluded women
who were currently using oral contraceptives and women who
had not completed 2 menstrual cycles since last using oral
contraceptives. Before participating, each subject read a de-
scription of the study and signed an informed consent form
approved by the university’s institutional review board, which
also approved the study.
Procedures
The evening before the supplementation period began, each
subject reported to the university’s General Clinical Research
Center for an overnight stay and for baseline measurements.
We instructed the subjects to refrain from any type of exercise
after the last meal of the day before being admitted for the
overnight stay. To control for changes in fluid distribution
across the menstrual cycle, each woman began the study be-
tween days 1 and 7 of the cycle. Upon arrival at the Center,
venous blood and urine samples were taken for a complete
clinical chemistry panel (20 items) and for drugs of abuse,
anabolic steroid, and pregnancy screen. After an overnight
fast, we measured each subject for body mass, urinary Cr and
creatinine concentrations, total body water (TBW) content, ex-
tracellular water (ECW) content, and muscle Cr concentration.
Once these measurements were completed, the supplementa-
tion period began. We instructed the subjects to maintain their
normal diets and their regular resistance-training programs
throughout the entire supplementation and testing period. We
also instructed the subjects to refrain from ingesting any type
of nonsteroidal anti-inflammatory medication, nutritional sup-
plement, or substance classified as a diuretic other than the
caffeine found in the habitual diet. Each subject was required
to maintain a training log in which the number of sets, repe-
titions, and the resistance used were recorded during each ex-
ercise session. Additionally, we asked each subject to complete
a weekly questionnaire designed to determine the incidence of
any adverse effects during supplementation. All subjects re-
ported back to the Center on the evening of the seventh and
28th (final) day of supplementation, at which time the over-
night fast and subsequent measurements were repeated.
Supplementation
We randomly assigned each subject to either a Cr supple-
mentation group or a P group in a double-blind fashion. Sub-
jects in the Cr group (8 men, 8 women) ingested 5.0 g of
Phosphagen (Experimental and Applied Sciences, Inc, Golden,
CO) mixed with 15 g of a flavored simple carbohydrate 5
times per day for 7 days (loading phase). Immediately after
the loading phase, each subject ingested the same supplement
once a day for the remaining 21 days (maintenance phase).
Subjects in the P group (8 men, 8 women) ingested 20 g of
the flavored simple carbohydrate for 28 days using the same
protocol as the Cr group. Individual-dose packages, identical
in weight, were prepared for the Cr and the P groups and
dispensed weekly. We instructed the subjects to mix the pow-
der supplement with 16 oz (0.47 L) of water and maintain a
daily record of the supplementation times. Finally, to further
monitor compliance, we asked each subject to return any un-
used portions at the end of each week.
Measurements
Urinary Creatine and Creatinine. Urine samples were
collected and frozen at 2808C for later analysis of Cr and
creatinine concentrations using high-performance liquid chro-
matography.
Muscle Creatine Concentration. After local anesthesia and
incision of the skin, muscle samples were obtained from the
vastus lateralis muscle of the nondominant leg using a per-
cutaneous needle-biopsy technique modified to include suc-
tion.
20
Immediately after removal, the tissue samples were fro-
zen in liquid nitrogen and stored at 2808C for later analysis.
When all testing sessions were completed, the tissue samples
were packaged in dry ice and shipped overnight to a human
performance laboratory, where they were later freeze dried,
dissected free of any blood and connective tissue, and pow-
dered. The powdered muscle was then extracted with perchlo-
ric acid, neutralized, and analyzed enzymatically for muscle
Cr using a spectrophotometric analysis described by Harris et
al.
20
Body Mass and Total Body Water Volume. Body mass
was assessed using a digital scale from the BOD POD Body
Composition Tracking System (Life Measurements, Inc, Con-
cord, CA). Total body water was determined using a deuterium
oxide dilution method, which has been shown to be a valid
and reliable measurement technique.
21–24
We administered
each subject an oral dose of deuterium oxide of approximately
0.15 g/kg of body mass, which was weighed out and diluted
with sterile water for intake. Before ingestion and after a 4-
hour equilibration period, two 5-mL venous blood samples
were drawn for comparison. After extraction from the blood,
the plasma was frozen at 2208C and stored for later analysis.
Samples were then packaged with dry ice and shipped over-
night to Metabolic Solutions, Inc (Nashua, NH), where deu-
terium enrichment in the body fluid was measured using iso-
tope ratio mass spectrometry.
22,24
The precision of this method
is 62%, and the percent coefficient of variation is typically
46 Volume 38
•
Number 1
•
March 2003
Urinary and Muscle Creatine, Body Mass, Total Body Water, and Intracellular Water After Loading and Maintenance with Either
Creatine or Placebo
Group and
Measurement
Presupplementation
(mean 6 SD)
Day 7
(mean 6 SD)
Day 28
(mean 6 SD)
Creatine
Urinary creatine (mg/dL)
Muscle creatine (mg/kg dm‡)
Body mass (kg)
Total body water (L)
Intracellular water (L)
14.09 6 35.62
123.18 6 11.78
75.54 6 17.67*
41.98 6 11.78
24.44 6 7.40
454.09 6 290.74*†
146.99 6 25.63*†
76.29 6 18.04*
43.35 6 12.19*†
25.39 6 8.03
331.26 6 272.34*†
143.58 6 18.84*†
76.86 6 18.07*†
44.02 6 12.37*†
25.57 6 8.66
Placebo
Urinary creatine (mg/dL)
Muscle creatine (mg/kg dm)
Body mass (kg)
Total body water (L)
Intracellular water (L)
8.12 6 7.52
127.99 6 13.20
72.94 6 15.72
41.34 6 8.93
24.00 6 5.59
14.22 6 48.83
124.28 6 13.65
73.61 6 15.92
42.21 6 9.08†
24.08 6 6.19
6.15 6 5.98
126.50 6 19.02
73.28 6 16.05
42.23 6 9.11†
23.70 6 7.16
*Significantly greater than placebo group (
P
, .05).
†Significantly greater than presupplementation (
P
, .05).
‡dm indicates dry mass.
0.75% daily.
21
Total body water was calculated as the deute-
rium-dilution space divided by 1.04, which corrects for ex-
change of the deuterium with nonaqueous hydrogen of body
solids.
21,22
We also assessed TBW using a Xitron 4200 multi-
frequency bioelectrical impedance analyzer (Xitron Technol-
ogies Inc, San Diego, CA). This was performed as a backup
measure in case we were unable to perform the dilution anal-
ysis on the plasma samples.
Intracellular Water and Extracellular Water Volumes.
The ECW compartment was determined using a sodium bro-
mide dilution method.
25–27
We administered each subject an
oral dose of sodium bromide (approximately 60 mg/kg of body
mass) simultaneously with the deuterium oxide solution. The
same blood samples taken for the deuterium analysis were also
used for the sodium bromide analysis, with the bromide con-
centration in the serum ultrafiltrate determined by high-per-
formance liquid chromatography (Metabolic Solutions, Inc).
Because of the extreme sensitivity of this method, small quan-
tities of bromide can be administered for the analysis, allowing
for sufficient washout between measurement days.
26
The cor-
rected bromide space was calculated and used to determine the
ECW volume.
25–27
The intracellular water (ICW) volume was
calculated by subtracting the ECW volume from the TBW
volume.
Statistical Analysis
We used the Statistical Package for the Social Sciences soft-
ware (version 10.0, SPSS Inc, Chicago, IL) to perform the
statistical analysis of the raw data. All dependent measures
were analyzed using a 1-within (time), 2-between (group and
sex) mixed design with repeated-measures analyses of vari-
ance and Tukey Honestly Significant Difference post hoc tests
to test differences between means. For all statistical tests, the
alpha level was set at .05.
RESULTS
Blood and Urine Analyses
Analyses for anabolic steroids and drugs of abuse were neg-
ative for all subjects at each testing date, and no differences
were observed in either group for blood or urine creatinine
concentrations. However, the time-by-group (F
2,56
5 25.56,
P 5 .000) and time-by-sex (F
2,56
5 4.04, P 5 .023) interac-
tions for urinary Cr concentration were significant. The Cr
group had significantly greater urinary Cr concentrations on
days 7 and 28 as compared with presupplementation, whereas
no changes were observed in the P group (Table). Further-
more, women experienced greater urinary Cr concentrations
than did men on days 7 and 28.
Muscle Creatine Concentration
Assays for Cr could not be completed for 4 subjects (2 each
in the Cr and P groups); thus, these subjects were not included
in the Cr analysis. The time-by-group interaction was signifi-
cant (F
2,48
5 4.75, P 5 .013): the Cr group had a greater Cr
concentration on days 7 and 28 as compared with presupple-
mentation (see Table). No changes were observed in the P
group. No differences were observed when the men and wom-
en within the Cr group were compared before or after supple-
mentation.
Body Mass
A significant time-by-group interaction (F
2,56
5 3.30, P 5
.044) was observed for body mass, as the Cr group experi-
enced a significant increase from presupplementation to day
28 (see Table). The Cr group’s body mass on day 7 was 0.75
kg greater than at presupplementation; however, this change
was not significant. The Tukey post hoc test revealed that an
increase of 0.88 kg was necessary for statistical significance.
The P group did not experience any significant changes in
body mass. As expected, men had greater body mass than
women, but there were no significant sex interactions.
Total Body Water Volume
A significant time-by-group interaction (F
2,56
5 3.86, P 5
.027) was observed for TBW (see Table). Both groups expe-
rienced significantly greater TBW levels on days 7 and 28 as
compared with presupplementation, but the increase was great-
er in the Cr group. The Tukey post hoc test revealed that a
Journal of Athletic Training 47
difference of 0.86 L was necessary for statistical significance.
The differences of 0.87 and 0.89 L experienced by the P group
were just higher than this value. Although no difference ex-
isted between the groups before supplementation, the Cr group
had a significantly greater TBW volume on days 7 and 28
than did the P group. As expected, men had a greater TBW
than women; however, there were no significant sex interac-
tions.
Extracellular Water and Intracellular Water Volumes
As expected, men had greater ICW and ECW volumes, but
there were no sex interactions. No other significant main ef-
fects or interactions, including a time-by-group interaction
(F
2,56
5 1.02, P 5 .366) for ICW, were observed. Further-
more, when ICW was expressed relative to the TBW, no sig-
nificant changes were noted.
DISCUSSION
We examined the changes in muscle Cr, body mass, and
body water during periods of Cr loading and maintenance in
men and women. The supplementation protocol was indeed
effective for increasing muscle Cr concentrations. The increas-
es in muscle Cr were associated with increases in both TBW
and body mass. However, only TBW increased during the
loading phase, whereas the increase in body mass was not
observed until both the loading and maintenance phases were
completed.
Muscle Creatine
Several reports indicate that muscle Cr concentration can be
elevated when a normal diet is supplemented with oral Cr.
1–4
Our Cr group experienced a 20% increase in Cr concentration
during the first week (loading phase) of supplementation. This
increase was then maintained throughout the remaining 3
weeks (maintenance phase).
As expected, a large amount of between-subject variability
was observed for the change in muscle Cr concentration from
presupplementation to the end of the loading phase. Similar
findings have been reported previously,
1–3
which may explain
why some individuals do not experience an ergogenic ef-
fect.
15,16
Greenhaff
28
reported that 20% to 30% of individuals
do not respond to Cr supplementation (,10 mmol/kg dry mass
[dm] [8%] in muscle Cr concentration). Similarly, we ob-
served that 4 subjects (28%) in our study failed to respond to
the supplementation. The dosages we used were not adjusted
for body mass; thus, each subject ingested equal amounts of
Cr. Because of this, it might be expected that a greater effect
would be seen in individuals with smaller body mass. How-
ever, this was not observed because the nonresponders repre-
sented a wide range of body mass (57.09–86.21 kg). Further-
more, the increase experienced by women (body mass 5 63.63
6 12.58 kg) was not different from that experienced by men
(body mass 5 87.46 6 11.98 kg). This is not unexpected
because the 7-day loading protocol should have been sufficient
for maximizing muscle uptake regardless of body mass.
1
For
example, women ingesting Cr experienced a greater increase
in urinary Cr excretion than did men after both the loading
and maintenance phases. Although sex differences have not
been reported previously, they are not unexpected. Any Cr not
taken in by the muscle or other tissues remains in the plasma
and is eventually filtered through the kidneys and excreted in
the urine. Because of their lower body mass, women had less
available tissue for Cr uptake, resulting in a greater amount of
excess Cr. Thus, factors other than the relative dose-response
relationship play a role in the total Cr uptake by the muscle.
Greenhaff
28
observed that 20% of individuals achieved Cr
concentrations of approximately 150 to 160 mmol/kg dm after
supplementation. This concentration is considered to be the
upper limit of muscle Cr stores, although some individuals,
including 4 subjects in the present study, achieve higher levels.
Whereas a number of factors have been suggested to affect
muscle Cr uptake, the primary determinant appears to be the
initial muscle Cr concentration.
1,3,28
The normal muscle Cr
concentration of the human vastus lateralis appears to be ap-
proximately 124 mmol/kg dm.
2,20
In our subjects, the average
muscle Cr concentration before supplementation was 125.6
mmol/kg dm, with a large amount of between-subject vari-
ability (105.9–150.8 mmol/kg dm). Our findings are consistent
with those of previous authors,
1–3
who reported a wide vari-
ation (100–150 mmol/kg dm) in the initial muscle Cr content.
Increases in muscle Cr concentration after supplementation ap-
pear to be inversely related to the initial Cr concentration.
1,28
In support of the above, we observed a significant correla-
tion between the initial Cr levels and the increases in muscle
Cr after supplementation (r 520.75, P , .01). Subjects in
the Cr group with an initial Cr concentration less than 120
mmol/kg dm experienced an average increase of 33.4
mmol/kg dm (23.1%), whereas subjects with an initial Cr con-
centration greater than 120 mmol/kg dm only experienced an
average increase of 16.6 mmol/kg dm (11.2%) during the load-
ing phase.
Body Mass
Previous investigators
8,11,13,16
have reported increases in
body mass after a loading phase of Cr supplementation. Al-
though the Cr group did experience an increase in the present
study, the increase did not reach significance until the entire
supplementation protocol had been completed (1.31-kg in-
crease after 28 days). In contrast, the P group failed to expe-
rience any significant changes in body mass. This is consistent
with other studies reporting increases after a protocol of Cr
loading and maintenance.
6,7,17–19
However, body mass mea-
surements were not taken immediately after the loading phase
in those studies. Thus, whether their subjects experienced any
immediate changes in body mass is unknown. In our study,
the increase observed in the Cr group after the loading phase
(0.75 kg) was slightly lower than what the Tukey post hoc test
demonstrated as necessary for significance (0.88 kg). This was
unexpected because increases of 0.70 and 0.75 kg after loading
had previously been found to be statistically significant.
11,16
However, our findings are not isolated because others
12,14,29,30
have also failed to observe significant body mass changes after
a loading phase of supplementation.
Although 4 subjects (including 3 women) in the Cr group
failed to experience an increase in body mass after 28 days of
supplementation, the range for those who did was consistent
with gains previously observed, from 0.47 to 3.92 kg.
6,7,17–19
At this time, the exact cause of the weight gain has not been
determined. However, increases in protein synthesis and water
retention are the 2 more commonly cited theories.
Protein Synthesis. It has been theorized that at least part
of the increase in body mass can be attributed to increased
48 Volume 38
•
Number 1
•
March 2003
protein synthesis and morphologic changes within the skeletal
muscle.
13
Recently reported data suggest that Cr supplemen-
tation might amplify protein synthesis stimulation in response
to resistance training.
31
In that study, however, protein content
was only examined after 12 weeks of supplementation and
training. Thus, the effect of Cr after only 1 week or even after
4 weeks of training is unknown. As mentioned previously,
because a number of authors
8,11,13,16
reported increases in
body mass in as few as 5 to 7 days, it is unlikely that these
changes can be explained by protein synthesis alone.
Water Retention. The gains in body mass observed are
likely due to water retention during supplementation. Creatine
is an osmotically active substance. Thus, any increase in the
body’s Cr content should result in increased water retention
and consequent gains in body mass.
2,8
For example, 1 subject
in the present study, who reported having a fairly consistent
body mass throughout the previous year, experienced a 4.8-kg
increase in body mass during the first week of supplementa-
tion, 90% of which was accounted for by the increase in TBW.
The limited number of investigators
12,17–19,32
who have re-
ported TBW volumes during supplementation provide con-
trasting results. Significant increases in TBW have been ob-
served after 6
19
and 9
17
weeks of supplementation, whereas a
similar 4-week protocol failed to affect TBW.
32
However,
whether the subjects in these studies actually experienced an
increase in muscle Cr is unknown because Cr concentrations
were not measured. Furthermore, in each of these studies, a
bioelectric impedance analysis was used to estimate TBW.
Such analysis is a prediction of TBW and is associated with
errors ranging from 1.5 to 2.5 L.
33
Dilution techniques, such
as the deuterium oxide and sodium bromide we used, are con-
sidered criterion measures of body water.
34,35
To our knowl-
edge, we are the first to directly measure muscle Cr and fluid
balance during supplementation, and our results suggest that
increases in muscle Cr concentrations are associated with wa-
ter retention. Both groups had similar TBW volumes at the
beginning of the study. However, although both groups ex-
perienced an increase in TBW during the first week of sup-
plementation, the Cr group’s TBW was significantly greater
than the P group’s TBW after both the loading and mainte-
nance phases (see Table). These findings support previous re-
search because the increase experienced by the Cr group
(4.86%) is similar to that observed using the bioelectric im-
pedance analysis measure (5.30% and 4.47%).
17,19
We initially theorized that water retention would be respon-
sible for the immediate gains in body mass after supplemen-
tation. As expected, the changes in TBW experienced by the
Cr group were similar to those observed for body mass. The
greatest increase in TBW (1.37 L) occurred during the first
week of supplementation, whereas the greatest difference com-
pared with presupplementation occurred after 28 days of sup-
plementation (2.04 L). It is interesting to note, however, that
the increase in TBW we observed would actually account for
a greater increase in body mass. We would expect that a TBW
increase of 1.37 L would be associated with a body mass in-
crease of approximately 1.37 kg. Yet, the Cr group only ex-
perienced a nonsignificant 0.75-kg increase during this time.
An explanation for this finding is not readily apparent but must
involve decreased caloric intake or increased caloric expen-
diture (or both) during supplementation. A BOD POD Body
Composition Tracking System digital scale was used for all
body mass measurements, and a dilution technique was used
to determine TBW. We also performed a bioelectric impedance
analysis assessment of TBW as a secondary measure. When
we analyzed these data, we observed a significant and identical
1.37-L increase in TBW after the loading phase. Thus, we do
not question the validity of our data.
Fluid Intake. During the loading phase, the subjects in both
groups ingested their respective supplements with approxi-
mately 454 mL of water 5 times per day. It is possible that
the increase in TBW content is the result of an increased fluid
intake during the week (;15.89 L). This is the most likely
explanation for the slight increase experienced by the P group.
However, the greater increase experienced by the Cr group
suggests that the subjects experienced greater water retention.
Thus, Cr uptake may have influenced water retention. Because
fluid intake and urinary volume were not assessed, we could
not determine whether increased fluid intake or decreased fluid
loss or both were responsible for the change in body water.
Caloric Intake and Expenditure. We instructed our sub-
jects to maintain their normal, habitual diet throughout the
supplementation period. Although we did not record dietary
intake, other authors
8,10,18
have reported consistent caloric in-
takes while increases in body mass occurred during supple-
mentation. Anecdotally, our subjects reported a decreased ap-
petite at times during the supplementation period because they
described a ‘‘full’’ feeling from ingesting the supplement and
fluid on 5 occasions each day. Decreases in caloric intake dur-
ing supplementation have been previously reported.
6,7
Unfor-
tunately, TBW volumes were not assessed in those studies;
thus, it is unknown if they increased or not. It is also possible
that the subjects in the Cr group experienced an ergogenic
effect, allowing for greater training volume during this period.
This may have resulted in greater caloric expenditure. Thus,
it is possible that increased fluid intake, decreased caloric in-
take, and increased caloric expenditure are responsible for our
findings.
Intracellular Water Retention. Because Cr is primarily
stored intramuscularly (95%), it is more likely that the increase
in TBW would be intracellular because of the direct influx of
water into the muscle cell. Previous investigators
12,18,32
were
unable to determine whether increases in lean body mass were
due to cellular water retention or gains in actual muscle pro-
tein, because only TBW was assessed during supplementation.
More recently, however, fluid distribution has been assessed
but only using the bioelectric impedance analysis predic-
tion.
17,19
We directly measured fluid distribution using dilution
techniques and observed a 1.13-L (4.62%) increase in ICW in
the Cr group. However, this change was not statistically sig-
nificant. Increases in ICW have been reported previously using
the bioelectric impedance analysis prediction.
17,19
In those
studies, increases of 3.30 L (9.0%) and 1.00 L (4.93%) were
statistically significant.
The nonsignificant increase we observed accounted for
55.4% of the increase in TBW volume, which is fairly con-
sistent with normal fluid distribution (approximately two thirds
of the TBW is intracellular). This suggests an equal distribu-
tion of fluid during supplementation. Interestingly, an increase
in cell volume appears to be an anabolic proliferative signal,
which may be the first step in muscle protein synthesis.
36,37
Because of this, increased cell volume has been suggested as
a mechanism for protein synthesis stimulation and increased
muscle mass under conditions of muscular overload during Cr
supplementation.
7,8
Journal of Athletic Training 49
Adverse Effects
None of the blood or urinary measures suggested any ad-
verse effects as a result of supplementation. Furthermore, none
of the subjects in the present investigation experienced muscle
cramping or any other side effects (other than increased body
mass) during the supplementation protocol. However, whether
any subjects performed exercise bouts resulting in a large
amount of water loss is unknown. Thus, a potential relation-
ship between Cr supplementation and heat illness cannot be
established from the results of the present investigation.
Limitations of the Study
As mentioned previously, caloric and fluid intakes were not
recorded, and differences in either of these factors could have
influenced the changes in body mass and fluid balance. Fur-
thermore, each subject was involved in an individualized re-
sistance training program. These training protocols were not
controlled for; however, the volume of each training session
was recorded. Because of a large amount of variability across
subjects, a relationship between training volume and changes
in body mass and fluid balance could not be established. Fur-
thermore, training protocols before supplementation were not
recorded, so comparisons could not be made. Thus, it is pos-
sible that the differences in training volume may also have
influenced the changes in body mass and fluid balance.
6,38,39
CONCLUSIONS
Our results indicate that the supplementation protocol was
effective in increasing muscle Cr concentrations. Increased
muscle Cr content was associated with an increased body mass
and TBW volume. Thus, supplementation does result in water
retention. It was initially hypothesized that the water would be
preferentially retained intracellularly, altering fluid distribu-
tion. However, this was not observed. Therefore, the theory
of a Cr-related fluid shift is not supported because fluid dis-
tribution remained normal. An alteration in fluid distribution
during supplementation had been suggested as a cause of mus-
cle cramping and other heat-related problems anecdotally as-
sociated with Cr supplementation. Because the subjects failed
to experience any side effects beyond weight gain, it cannot
be determined whether athletes supplementing their habitual
diet with oral Cr monohydrate will be more predisposed to
muscle cramping and heat illness than athletes who are not
ingesting Cr. However, our results do not support the fluid-
shift theory behind Cr supplementation and heat illness. Thus,
from this investigation, a potential relationship between Cr
supplementation and heat illness cannot be established. It will
be of value for future researchers to focus on changes in fluid
balance and the occurrence of heat illness when Cr supple-
mentation is combined with fluid loss during exercise.
ACKNOWLEDGMENTS
This work was supported in part by a grant from the National
Athletic Trainers’ Association Research and Education Foundation
and in part by a grant from the National Institutes of Health to the
University of Virginia, General Clinical Research Center, MO1
RR00847. We thank Dr Lori Wideman, Dr Judy Weltman, Sandra
Jackson, RN, and the University of Virginia General Clinical Re-
search Center staff for their assistance during the data collection. We
also thank Experimental and Applied Sciences (EAS) Inc, Golden,
CO, for supplying the Cr monohydrate used in the investigation.
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