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Rahimi, R. et al.: CREATINE SUPPLEMENTATION ALTERS THE HORMONAL ... Kinesiology 42(2010) 1:28-35
28
CREATINE SUPPLEMENTATION ALTERS THE HORMONAL
RESPONSE TO RESISTANCE EXERCISE
Rahman Rahimi
1
, Hassan Faraji
2
, Dariush Sheikholeslami Vatani
3
and Mohammad Qaderi
4
1,4
Department of Physical Education & Sport Science,
Islamic Azad University Branch of Mahabad, Mahabad, Iran
2
Department of Physical Education & Sport Science,
Azad University Branch of Marivan, Marivan, Iran
3
Department of Physical Education & Sport Science, University of Kurdistan, Sanandaj, Iran
Original scientific paper
UDC 591.1:577.1:796.015.8-055.1 (35)
Abstract:
The purpose of this study was to determine the influence of short-term creatine supplementation on
hormonal responses to resistance exercise. 27 trained men were randomly divided into a creatine supplementation
group [the CR group (n=15), taking 4×5 g creatine monohydrate/day] or a placebo supplementation group
[the PL group (n=12), taking 4×7.5 g maltodextrin/day]. A double-blind research design was employed for
a 7-day supplementation period. After this period, the participants performed exercise testing. Blood tests
occurred on day 1 prior to supplementation loading (1Pre) and after this period [on the exercise testing day:
pre-exercise (Pre), immediately post-exercise (IP), and 15 (15P) and 30 (30P) minutes post-exercise] for
the measurement of the serum growth hormone and testosterone concentrations. Significant differences in
the number of repetitions and volume were seen with CR (7.2±1.3 repetitions, 1560±386 kg) compared to
PL (5.6±2 repetitions, 1089±341 kg) at set 5 of the exercise protocol (p=.01). Serum growth hormone and
testosterone were significantly higher at 15P in CR (6.1±1.8 ng/ml, 70.1±19 pmol/L) compared to PL (4.1±1.7
ng/ml, 44.8±16 pmol/L) [(p=.02), (p=.01)]. The enhanced exercise performance resulted in a significantly
greater increase in both the growth hormone and testosterone concentrations, indicating an augmented
anabolic hormone response to creatine supplementation.
Key words: creatine loading, anabolic hormones, growth hormone, testosterone, exercise performance
Introduction
Resistance exercise stimulates the release
of various anabolic hormones, especially the
growth hormone and testosterone. The hormonal
response to resistance exercise potentiates gains
in muscle strength following chronic training
(Hansen, Kvorning, Kjaer, & Sjogaard, 2001).
The growth hormone stimulates protein synthesis
by activating ribosomal initiation factors thereby
improving translational effi ciency (Bush, et al.,
2003). Alternately, testosterone increases protein
synthesis by converting the androgen receptor to
a transcription factor and by activating muscle
satellite cells, important because gene transcription
is an initial target for the modulation of protein
synthesis (Herbst & Bhasin, 2004). Because of the
critical functions of hormones, various methods
were explored to enhance the exercise–endocrine
interaction. For instance, feeding participants
before and/or immediately after resistance exercise
alters the hormonal response, up-regulates the
androgen receptor content (Kraemer, et al., 2006),
and, ultimately, increases muscle protein synthesis
(Rasmussen & Phillips, 2003). In addition to
feeding, various nutritional supplements (herbs and
micronutrients) improve responses and adaptations
to resistance exercise. Creatine supplementation
as a nutritional supplement positively affects
strength development (Kraemer, et al., 2007,
2006; Gotshalk, et al., 2008; Rawson & Volek,
2003). This supplementation also increases the lean
muscle mass, total work performed and muscular
power; alters body composition and hydration status
(Volek, Boetes, Bush, 1997; Rawson & Persky,
2007; Rawson & Volek, 2003). The coordinated
function of metabolically connected nutrients (such
as creatine supplementation) and physiologically
active ingredients may be pivotal in enhancing
Rahimi, R. et al.: CREATINE SUPPLEMENTATION ALTERS THE HORMONAL ... Kinesiology 42(2010) 1:28-35
29
hormonal responses and enhancing performance.
Moreover, because creatine supplementation
rapidly increases body mass and fat-free mass
(Rawson & Volek, 2003), it has been hypothesised
that creatine induces hypertrophy through the
endocrine mechanisms. However, there have been
few studies investigating the effects of short-term
creatine supplementation on anabolic hormones
and these have produced confl icting results. For
example, Volek, et al. (1997) assessed testosterone
and cortisol immediately post-exercise (5 sets of
bench presses and jump squats) in creatine (25 g/d
for 7 days) and placebo-supplemented participants,
and found no effect of creatine on the endocrine
status. Schedel, et al. (2000), however, found
increased growth hormone levels (83%) in response
to a 20 g oral creatine bolus. Despite this, Op‘t
Eijnde and Hespel (2001) reported that creatine
supplementation (20 g/day for 5 days) did not alter
cortisol and growth hormone responses to a single
bout of heavy resistance exercise. Therefore, it was
the purpose of this study to examine the effect of the
short-term creatine supplementation on resistance
exercise and hormonal response.
Methods
Participants
Twenty-seven men volunteered to participate
in this study. These participants were randomly
divided into either a creatine supplementation
CR [age: 21.6±3.6 years, height: 1.74±.08 m,
body mass: 71.93±7.82 kg] or a placebo PL [age:
21.2±3.2 years, height: 1.71±.06 m, body mass:
69.12±10.46 kg] supplementation group. There
were no signifi cant differences between the groups
in physical characteristics. All subjects were
healthy, with no major chronic diseases such as
diabetes, cardiovascular disease, atherosclerosis,
hypertension, or dyslipidemia.
The study was limited to the males to reduce
variation in hormonal response to the resistance
exercise. All participants were informed of the
purpose, procedures and possible risks of the
investigation before they gave written informed
consent to participate in the study. All of them
reported being free of any anabolic supplements
or drugs during the previous year. Participants
who consumed the creatine supplementation for
at least 5 months before the start of this study
or presented body mass index ≥24 kg/m
2
were
excluded. The Institutional Review Board of the
University approved the research protocol. The
participants refrained from any additional nutrition
supplementation during this study. Each participant
was currently resistance-trained for a minimum of a
year using standard multi-set; multi-exercise train-
ing protocols typical of health/fi tness resistance
exercise programmes directed at develop-ing muscle
strength, size and power and reported for training
at least three times per week. All participants also
reported taking part in club sport activities (such
as mini-football) on a weekly basis, but none were
competitive athletes.
Procedure
A within treatment, randomized, double blind
placebo (PL)-controlled protocol was used to inves-
tigate the effects of a creatine supplement (CR) on
anabolic hormones and exercise performance in
a bout of resistance exercise. Two familiarization
sessions were used to determine the maximal strength
test (1RM) one week prior to the study. Participants
reported then to the human performance laboratory
on 6 separate occasions. During the initial visit,
participants performed the 1RM with the squat
exercise. After the 1RM testing, participants were
randomly divided into the CR (n=15) or PL (n=12)
group. On the second, third and fourth visits (72
hours between each visit), participants performed
familiarization sessions with the exercise protocol (6
sets of up to 10 repetitions with 80% of their 1RM)
to ensure the proper technique and reliability of the
testing methods. On the fi fth visit (before the start
of the creatine loading) blood tests were obtained
and the participants took the supplements (CR or
PL) for 7 days. The participants then returned to
the human performance laboratory for their fi nal
exercise session. Thirty minutes after consumption
of the pre-exercise supplementation, the participants
began the experimental protocol. Blood tests were
obtained on day 1 prior to ingesting the supplements
(1Pre), on the acute resistance exercise protocol
(AREP) day (after 7 days): 30 minutes after ingesting
the supplement, which was immediately before
exercising (Pre), immediately post-exercise (IP),
and 15 (15P) and 30 (30P) minutes post-exercise.
All the tests were scheduled at the same time of
day (17:00 h) to negate any confounding infl uences
of diurnal hormonal variations. The experimental
design is depicted in Figure 1.
Maximal strength testing
The 1RM squat test was performed using
methods previously described by Hoffman (2006).
Each participant performed a warm-up set using
a resistance that was approximately 40-60% of
his perceived maximum and then performed 3-4
subsequent trials to determine the 1RM. A 3- to
5-minute rest period was provided between each
trial. The squat exercise required the participant to
place an Olympic bar across the trapezius muscle
at a self-selected location, which was attained when
the greater trochanter of the femur reached the same
level as the knee. The participant then stood up until
full knee extension. Trials not meeting the range of
motion criteria were discarded.
Rahimi, R. et al.: CREATINE SUPPLEMENTATION ALTERS THE HORMONAL ... Kinesiology 42(2010) 1:28-35
30
Supplement procedure
The CR group consumed 5.0 g creatine
monohydrate (Creatine Fuel, Twin Laboratories,
Hauppauge, USA), 4 times a day for 7 days. The
PL group ingested 7.5 g maltodextrin, which
was matched with the creatine powder for taste
and colour. The participants mixed the powder
in approximately 150 ml of warm water for
better dissolution of the creatine monohydrate
or maltodextrin and consumed this solution
immediately after preparation. The supplement
was ingested 4 times a day, with breakfast, lunch,
dinner and before sleep. They did not do any specifi c
activity, such as resistance training or jogging,
during this experimental period. On the AREP
day, participants ingested the supplement in the
laboratory immediately after a resting blood tests,
which was 30 minutes before they began the AREP.
All participants were encouraged to adhere to their
normal and similar dietary patterns throughout the
study [carbohydrate (CR: 63.7 ± 4.2, PL: 64.6 ± 6.4),
protein (CR: 13.6 ± 3.8, PL: 12.8 ± 4.2), fat (CR: 23.8
± 6.8, PL: 23.5 ± 3.6)]. Participants were asked to
refrain from exercise and from any alcohol for 24-h
prior to each protocol day.
Acute resistance exercise protocol
(AREP)
The AREP consisted of: (1) a standardized
dynamic warm-up with no stretching, (2) 6 sets of
squats exercise up to 10 repetitions per set at 80% of
the individual’s pre-determined 1RM. A 2-minute
rest period was provided between each set. The
volume of each set was calculated as the number
of complete repetitions completed × resistance
used.
Body composition
Body composition was determined by the skin-
fold method with a Lange skinfold calliper using
standard techniques. Body density was derived
from the Jackson–Pollock method and the equa-
tion with age as a component (Pollock & Jackson,
1984). The three-compartment Siri equation was
used for percent body fat (Siri, 1961); for young men
this equation has a high correlation (r=.997) with
the Heymsfi eld four-compartment model as crite-
rion measure of % body fat (Clasey, et al., 1999).
Height and body mass were assessed by the Detecto
Certifi er scale and height rod.
Blood collection and hormonal analyses
Blood samples were centrifuged at 1,500 × g,
harvested for serum and plasma, and stored at
−80°C until analysed. Venous blood samples,
in all sampling, were taken via an in-dwelling
catheter inserted in a superfi cial arm vein, in a
supine position, and kept patent with a 1:10 heparin/
saline solution. Serum total growth hormone and
testosterone were determined in duplicate by using
standard radioimmunoassay procedures and were
assayed via Spectria kits (Diagnostic Products,
Finland). The detection limits of the growth hormone
and testosterone were .04 ng
·
ml
-1
and .13 nmol
·
L
-1
,
respectively. All hormones were measured in the
same assay on the same day to avoid inter-assay
variance. Intra-assay variance was below 3% for
all analyses.
Statistical analysis
Descriptive physical characteristics of CR and
PL participants were compared with the dependent
group’s t-test. Statistical evaluation of the data was
accomplished by using a two-way analysis of variance
with repeated-measures design. The two factors
were supplement condition (creatine vs placebo) and
repeated measures (pre- and post-exercise blood
samples over time). When a signifi cant F value
was achieved, a Fisher’s least signifi cant difference
(LSD) post hoc test was used to locate the pairwise
differences between means. Dependent t-tests were
used to analyse total repetitions and total training
volume performed during the exercise protocols.
The level of signifi cance for this investigation was
set at p<.05. All data are reported as mean ± SD.
Figure 1. Experimental design
1RM
testing
Familiarization
sessions
72-96 h
between
each session
Blood draw
(1Pre)
7 days supplementation loading
A
cute
resistance
exercise
protocol
Blood draws
Pre exercise IP 15P 30P
Rahimi, R. et al.: CREATINE SUPPLEMENTATION ALTERS THE HORMONAL ... Kinesiology 42(2010) 1:28-35
31
Sets
Figure 3. Comparisons of training volume (mean ± SD)
between sets. *Significant difference between the creatine
supplementation and placebo exercise sessions
*
0
500
1000
1500
2000
2500
3000
1 2 3 4 5 6
Placebo
Creatine
*
kg
§
*
§
§
0
1
2
3
4
5
6
7
8
9
1Pre
Pre
IP
15P
30P
ng
/
ml
Placebo
Creatine
0
1
2
3
4
5
6
7
8
9
1Pre
Pre
IP
15P
30P
Placebo
Creatine
§
*
§
§
ng/ml
Figure 4. Comparisons of serum growth hormone (GH)
concentrations (mean ± SD) for various time points.
*Significant difference between the creatine supplementation
and placebo exercise sessions. §Significantly different from
before exercise
*
§
0
10
20
30
40
50
60
70
80
90
100
1Pre
Pre
IP
15P
30P
mol
Placebo
Creatine
0
10
20
30
40
50
60
70
80
90
100
1Pre
Pre
IP
15P
30P
Placebo
Creatine
*
§
pmol/L
Figure 5. Comparisons of serum free testosterone
concentrations (mean ± SD) for various time points.
*Significant difference between the creatine supplementation
and placebo exercise sessions. §Significantly different from
before exercise
Results
Performance
The number of repetitions completed per set
and the volume per set are shown in Figures 2
and 3, respectively. A signifi cant difference in the
number of repetitions and volume were seen with
CR (7.2±1.3 repetitions, 1560±386 kg) compared
to PL (5.6±2 repetitions, 1089±341 kg) at set 5 of
the exercise protocol (p=.01). No other signifi cant
differences between sets were observed.
Hormonal responses
Hormonal responses can be seen in Figures 4
and 5. There was no difference between CR and
PL in growth hormone and testosterone at the 1Pre
and Pre. No signifi cant changes were observed
following 7 days creatine loading in the growth
Figure 2. Comparisons of repetitions per set (mean ±
SD) per set. *Significant difference between the creatine
supplementation and placebo exercise sessions
0
1
2
3
4
5
6
7
8
9
10
11
1 2 3 4 5 6
Placebo
Creatine
*
Reps
Sets
hormone and testosterone per CR and PL (different
between the 1Pre and Pre). In AREP, the growth
hormone signifi cantly increased from Pre at 15P
and 30P for CR and 15P for PL. A signifi cantly
higher concentration of growth hormone was
observed in CR (6.1±1.8 ng/ml) at 15P compared to
the PL group (4.1±1.7 ng/ml) (p=.02). Testosterone
signifi cantly increased from Pre at 15P for CR.
Also, a signifi cantly higher concentration of
testosterone was observed in CR (70.1±19 pmol/L)
at 15P compared to the PL group (44.8±16 pmol/L)
(p=.01).
Body composition
The group of CR gained signifi cantly more
body mass (.72±.13 kg) and fat-free mass (.94 ±.08
kg) compared with the PL group’s (p=.03, p=.04,
respectively) (Table 1).
Rahimi, R. et al.: CREATINE SUPPLEMENTATION ALTERS THE HORMONAL ... Kinesiology 42(2010) 1:28-35
32
Discussion and conclusions
The results of this study indicate that 7 days of
creatine supplementation (20 g/day) with no physical
training enhance performance during a resistance
exercise training session as refl ected by an increase
in the number of repetitions performed and training
volume. These outcomes are similar to those found
in previous studies (Gotshalk, et al., 2002, 2008).
The mechanisms for these improvements likely
include increased availability of phosphocreatine
for ATP synthesis during contraction (Navratil, et
al., 2009), increased availability of free creatine
for phosphocreatine resynthesis during recovery
(Dawson, et al., 1995), and an improved muscle
buffering capacity (Terjung, et al., 2000). The signi-
fi cantly greater number of repetitions performed
and training volume for set 5 indicate that the
creatine supplementation appears to provide an
effective stimulus in improving acute resistance
exercise performance. The improvement in training
volume also appears to be refl ected in the hormonal
response to the exercise protocol. A greater anabolic
hormone response (e.g., testosterone and growth
hormone) could have an important implication in
the repair and recovery of skeletal muscle after
resistance exercise sessions and subsequently
play a vital role in the muscle remodeling. In the
present study, growth hormone concentrations
increased signifi cantly in response to the AREP
for both supplementation and placebo conditions
which was consistent with the results of Schedel,
et al. (2000). Also, the signifi cantly greater growth
hormone response to the exercise protocol is similar
to other studies that demonstrated the importance
of training volume on growth hormone increases
(Hoffman, et al., 2008; Boroujerdi & Rahimi,
2008; Godfrey, Madgwick, & Whyte, 2003). The
importance of a greater growth hormone response
to exercise cannot be understated in terms of muscle
signalling pathways. The growth hormone seems
to play an important role in protein synthesis via
the interaction with the growth hormone receptor
on the cell membrane (Godfrey, et al., 2003) and
subsequent increases in translational effi ciency
(Bush, et al., 2003).
The response of testosterone in this study
is similar to that found in other investigations
(Hoffman, et al., 2008). Their studies showed that
differences in training volume can infl uence the
total testosterone response to exercise. Thus, this
greater increase in testosterone is likely due to the
higher volume of work performed in the creatine
supplementation condition. Smilios, Pilianidis,
Karamouzis and Tokmakidis (2003) showed that
higher exercise volume at the same load can elicit
higher post-exercise testosterone concentrations.
Nevertheless, it indicates a higher anabolic response
in the signaling response to the exercise protocol.
Testosterone is an important mediator of the
adaptations to resistance exercise. Testosterone
amplifi es the synthesis of muscle contractile proteins
(Fer rando, et al., 1998), which is an impor tant par t of
the hypertrophic adaptation to resistance training.
Thus, enhanced testosterone concentrations in
the CR group suggest that resistance exercise
combined with creatine supplementation provides
a superior anabolic milieu. Although not measured,
the increase in growth hormone and testosterone
indicate that creatine supplementation might have
increased resistance exercise-induced muscle protein
synthesis. Growth hormone and testosterone have
been known as hormones involved in the anabolic
processes of muscle cells. Therefore, an increase of
muscle mass may be instigated by these hormones
(Hansen, et al., 2001). Despite of our data, Volek,
et al. (1997) and/or Op‘t Eijnde and Hespel (2001)
found no measurable alteration in endocrine status
after creatine supplementation to resistance exercise.
As the improvement in exercise volume seems to be
refl ected in the hormonal response to the exercise
protocol, the difference in the improvement of the
total volume of exercise between this study and their
researches may explain, in part, these discrepancies
in hormonal responses.
Because creatine supplementation rapidly
increases body mass and fat-free mass, we hypo-
thesised that creatine induces hypertrophy through
endocrine mechanisms. However, there were no
signifi cant alterations in resting circulating anabolic
hormones following 7 days of creatine loading.
These fi ndings are also consistent with the fi nding
of Volek, et al. (2004). The data presented here
showed that seven days of creatine supplementation
resulted in small but signifi cant increases in both
body mass and fat-free mass. These results are
similar to previous fi ndings (Gotshalk, et al., 2008).
Since there were no signifi cant alterations in resting
Table 1. Body composition responses
CR group PL group
Body mass (kg)
Pre
Post
Body fat (%)
Pre
Post
Body fat (kg)
Pre
Post
Fat-free mass (kg)
Pre
Post
71.93 ± 7.82
72.65 ± 10.48*
15.23 ± 4.12
15.08 ± 4.67
21.23 ± 4.51
21.37 ± 4.84
50.70 ± 6.11
51.28 ± 6.24*
69.12 ± 10.46
69.20 ± 11.12
16.71 ± 5.25
16.65 ± 5.89
11.55 ± 6.48
11.69 ± 6.53
57.57 ± 7.27
57.51 ± 7.55
Values are mean ± SD obtained from skinfold analyses
*p<.05 from Pre value for the CR group
Rahimi, R. et al.: CREATINE SUPPLEMENTATION ALTERS THE HORMONAL ... Kinesiology 42(2010) 1:28-35
33
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Received: November 10, 2009
Accepted: April 8, 2010
Correspondence to:
Rahman Rahimi
Department of Physical Education & Sport Science
Islamic Azad University Branch of Mahabad
Mahabad, Iran
E-mail: Rahman.Rahimi@yahoo.com
Rahimi, R. et al.: CREATINE SUPPLEMENTATION ALTERS THE HORMONAL ... Kinesiology 42(2010) 1:28-35
35
Cilj ovog istraživanja bio je utvrditi utjecaj krat-
kotrajne suplementacije kreatinom na hormonsku
reakciju organizma kod vježbi s opterećenjem. 27
treniranih muškaraca nasumično su podijeljeni u
grupu koja je uzimala kreatin [CR skupina (n=15),
4×5 g kreatin monohidrata po danu] ili u placebo
skupinu [PL grupa (n=12), 4×7.5 g maltodextrina
po danu]. Dvostruka anonimna metoda istraživanja
bila je korištena pri realizaciji sedmodnevnog
suplementacijskog perioda. Nakon perioda suple-
mentacije, provedena su finalna testiranja. Testi-
ranje krvnih uzoraka provedeno je prvog dana
eksperimenta neposredno prije suplementacije
(1Pre) i nakon eksperimentalnog perioda [na dan
finalnih testiranja: prije izvođenja vježbi s opte-
rećenjem (Pre), neposredno nakon izvođenja
vježbi s opterećenjem (IP), te 15 (15P) i 30 (30P)
minuta nakon izvođenja vježbi s opterećenjem]
za mjerenje koncentracije seruma hormona
SUPLEMENTACIJA KREATINOM MIJENJA HORMONALNU
REAKCIJU ORGANIZMA NA VJEŽBE S OPTEREĆENJEM
rasta i testosterona. Statistički značajne razlike u
broju ponavljanja i veličini ukupnog opterećenja
utvrđene su kod CR skupine (7.2±1.3 ponavljanja,
1560±386 kg) u usporedbi s PL skupinom (5.6±2
ponavljanja, 1089±341 kg) kod 5. serije provedenog
protokola vježbanja (p=.01). Serumi hormona
rasta i testosterona bili su statistički značajno veći
u 15P kod CR skupine (6.1±1.8 ng/ml, 70.1±19
pmol/L) u usporedbi s PL skupinom (4.1±1.7 ng/ml,
44.8±16 pmol/L) [(p=.02), (p=.01)]. Bolji rezultati u
finalnom testiranju kod CR skupine rezultirali su
statistički značajno većom koncentracijom hormona
rasta i testosterona u odnosu na PL skupinu, što
pokazuje povećanu reakciju anaboličkih hormona
na suplementaciju kreatinom.
Ključne riječi: punjenje kreatinom, anabolički
hormoni, hormon rasta, testosteron, izvedba vježbe
