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THE EFFECTS OF CREATINE SUPPLEMENTATION ON SPRINT RUNNING PERFORMANCE AND SELECTED HORMONAL RESPONSES Hassan FARAJI*, Hamid ARAZI**, Dariush SHEIKHOLESLAMI VATANI *** & Mehdi HAKIMI** * Department of Physical Education & Sport Science, Islamic Azad University Marivan Branch, Marivan, Iran **Faculty of Physical Education and Sport Science, University of Guilan, Rasht, Iran ***Department of Physical Education & Sport Science, University of Kurdistan, Sanandaj, Iran ABSTRACT The purpose of this study was to determine the influence of short-term creatine supplementation on sprint running performance (100 and 200 m) and circulating hormone [growth hormone (GH), testosterone and cortisol] concentrations. Twenty amateur male runners were randomly divided into a creatine supplementation group, or placebo group. Subjects were provided with capsules containing either creatine monohydrate or identical powdered cellulose placebo. Daily creatine monohydrate supplementation was 20 g/day parceled into three equal dosages to be consumed with each major meal. Subjects were tested for performance and resting blood hormone concentrations before and after six days. A double-blind research design was employed in this study. After this creatine loading, the mean running performance time of the creatine supplementation group decreased significantly in the 100 m, but not the 200 m. Serum GH, testosterone, and cortisol concentrations were not affected by creatine supplementation. It can therefore be concluded that although short-term creatine supplementation was found to improve sprint performance in the 100 m in amateur runners, this performance improvement did not appear to be hormonally mediated. Key words: Sprint performance; Creatine supplementation; Hormonal responses; Creatine loading.
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South African Journal for Research in Sport, Physical Education and Recreation, 2010, 32(2): 31-39.
Suid-Afrikaanse Tydskrif vir Navorsing in Sport, Liggaamlike Opvoedkunde en Ontspanning, 2010, 32(2): 31-39.
ISSN: 0379-9069
31
THE EFFECTS OF CREATINE SUPPLEMENTATION ON SPRINT
RUNNING PERFORMANCE AND SELECTED HORMONAL RESPONSES
Hassan FARAJI*, Hamid ARAZI**, Dariush SHEIKHOLESLAMI VATANI ***
& Mehdi HAKIMI**
* Department of Physical Education & Sport Science, Islamic Azad University Marivan
Branch, Marivan, Iran
**Faculty of Physical Education and Sport Science, University of Guilan, Rasht, Iran
***Department of Physical Education & Sport Science, University of Kurdistan,
Sanandaj, Iran
ABSTRACT
The purpose of this study was to determine the influence of short-term creatine
supplementation on sprint running performance (100 and 200 m) and circulating
hormone [growth hormone (GH), testosterone and cortisol] concentrations. Twenty
amateur male runners were randomly divided into a creatine supplementation
group, or placebo group. Subjects were provided with capsules containing either
creatine monohydrate or identical powdered cellulose placebo. Daily creatine
monohydrate supplementation was 20 g/day parceled into three equal dosages to be
consumed with each major meal. Subjects were tested for performance and resting
blood hormone concentrations before and after six days. A double-blind research
design was employed in this study. After this creatine loading, the mean running
performance time of the creatine supplementation group decreased significantly in
the 100 m, but not the 200 m. Serum GH, testosterone, and cortisol concentrations
were not affected by creatine supplementation. It can therefore be concluded that
although short-term creatine supplementation was found to improve sprint
performance in the 100 m in amateur runners, this performance improvement did not
appear to be hormonally mediated.
Key words: Sprint performance; Creatine supplementation; Hormonal
responses; Creatine loading.
INTRODUCTION
Creatine is a popular dietary supplement that is used by athletes to increase muscle mass and
strength and especially to improve sports performance (Kreider, 2003; Rawson & Persky,
2007). Supplementation thereof has been demonstrated to increase resting concentrations of
creatine and phosphocreatine in skeletal muscle (Navratil et al., 2009).
Gotshalk et al. (2008) reported that creatine supplementation (0.3 g/kg/day for seven days)
resulted in a significant increase in the amount of work performed during five sets of bench
press and jump squats in comparison to a placebo group. Mujika et al. (2000) found that
creatine supplementation (20 g/day for six days) improved repeated sprint performance (6×15
m sprints with 30 sec. recovery) and jumping ability in soccer players. In a study by Skare
SAJR SPER, 32(2), 2010 Faraji, Arazi, Sheikholeslami Vatani & Hikimi
32
and Skadberg (2001) creatine supplementation (20 g/day) also decreased 100 m sprint times
and reduced the total time of 6 × 60 m sprints in a group of well-trained adolescent
competitive runners.
Not all previous studies have, however, found that creatine supplementation enhances
exercise performance. Op’t Eijnde et al. (2001) reported that creatine (20 g/day for five days)
did not enhance stroke performance or 70 m agility sprint performance in well-trained tennis
players. Improvements in performance were also not identified during single or repetitive
sprint bouts (Greenhaff et al., 1993; Kinugasa et al., 2004) or in swimmers in 25, 50, and 100
m race distances (Mujika et al., 1996; Mendes et al., 2004). The scarcity of published reports
concerning single sprints lasting 6-60 sec., the lack of standardization of exercise protocols
and variations in individual training levels may account for these discrepant results and
suggest that additional studies are needed.
As creatine supplementation rapidly increases body mass and fat-free mass (Rawson &
Persky, 2007; Gotshalk et al., 2008), it has been hypothesised that creatine induces
hypertrophy through endocrine mechanisms. Few studies evaluating the effects of creatine
supplementation on performance have, however, included additional analysis of hormonal
responses on consecutive days and these have produced conflicting results. Volek et al.
(1997) assessed circulating testosterone and cortisol concentrations immediately post-exercise
(five sets of bench presses and jump squats) in creatine (25 g/d for seven days) and placebo
supplemented subjects and found no effect. Schedel et al. (2000), however, found increased
serum growth hormone (GH) concentrations (83%) in response to a 20 g oral creatine bolus.
These discrepancies in the findings may primarily be attributed to variations in the
performance level of subjects (amateur vs. elite), experimental protocol, gender and age. The
purpose of this study was therefore to determine the influence short-term creatine
supplementation on performance and hormonal responses to sprint running performance in
subjects who were modestly trained.
METHOD
Subjects
Twenty healthy young male amateur runners (mean age: 21 years) volunteered to participate
in this study. Because less intensively trained athletes may have a greater capacity to increase
their intramuscular stores of creatine than the elite athletes (Selsby et al., 2003), amateur
runners were selected to participate in this study. All subjects were informed of the purpose,
procedures and possible risks of the investigation before they gave written consent to
participate in the study. They were also required to confirm that they had not taken any
anabolic supplements or drugs during the previous year and had refrained from creatine
supplementation for at least three months before the start of this study. The Institutional
Review Board of the University approved the research protocol. The subjects had been doing
sprint training (100 and 110 m), twice per week for a period of at least three months and had
previously taken part in club sport activities (such as mini-football). The subjects refrained
from any additional nutrition supplementation and exercise during this study and were
encouraged to adhere to their usual dietary patterns. Before the study, subjects were assigned
SAJR SPER, 32(2), 2010 Creatine supplementation, sprinting and anabolic hormones
33
to a creatine supplementation (CR) or a placebo (PL) group using a randomized double-blind
design.
Experimental design
A double-blind, randomized study was employed using two experimental groups (creatine or
placebo supplementation) who underwent six days supplementation. After pre-testing (one
day later), subjects were provided with capsules containing either creatine monohydrate
(Creatine Fuel, Twin Laboratories, Inc., Hauppague, NY) or identical powdered cellulose
placebo. Daily creatine monohydrate supplementation was 20 g/day parceled into three equal
dosages to be consumed with each major meal. The subjects consumed the supplements for
six days.
Testing occurred before and at the end of six days of supplementation. Performance tests in
100 and 200 m sprint were started after the subjects underwent a standard warm-up. Fifteen
minutes of recovery was given between tests. Participations were asked to refrain from
exercise and from consumption of alcohol for 48 hours prior to each protocol day.
Body composition
Body composition was determined from seven skinfold sites (triceps, subscapular,
midaxillary, chest, suprailiac, abdomen, and thigh) according to the method of Lohman, et al.
(1988) using a Lange skinfold caliper. Skinfold measurements were based on the average of
two trials and obtained on the right side in serial fashion by the same investigator. Body
density was estimated using the age-adjusted equation of Pollock and Jackson (1984). The
three-compartment Siri equation was used for % body fat (Siri, 1961). Height and body mass
were assessed by digital scale (Japan) and height rod (Iran).
Blood collection and analyses
Blood samples were obtained via venipuncture, after five minutes in a supine position, from
an antecubital vein by using a 20-guage needle and vacutainer tubes for the determination of
serum testosterone, cortisol and GH concentration. Blood samples were obtained, pre and
after six days of supplementation (immediately after running tests), in the early morning
hours, and after a 10 hour overnight fast and occurred during a standardized time of day for
each subject in order to minimize the effects of diurnal hormonal variations. The blood was
processed and centrifuged, and the resultant serum was stored at −80°C until analyzed. Total
serum testosterone, cortisol and GH were determined in duplicate by using standard
radioimmunoassay procedures and were assayed via kits (Yellow Spring, OH).
Statistical analyses
Data are reported as mean ± SEM. A two-way analysis of variance (ANOVA) with repeated-
measures design was used to establish whether PL and CR treatments differed with time. In
the case of a significant F value, a Fisher’s least significant difference (LSD) post hoc test
was used to locate the exact time point of the differences between means. The level of
significance for this investigation was set at P<0.05.
SAJR SPER, 32(2), 2010 Faraji, Arazi, Sheikholeslami Vatani & Hikimi
34
RESULTS
Physical characteristics and dietary intakes of the subjects
There were no significant differences between groups in terms of mean (± SD) physical
characteristics. In the CR group these included age (21.75 ± 1.32 years), height (176.32 ±
6.35 cm), body mass (69.16 ± 8.65 kg) and percent body fat (16.12 ± 4.12% ), whereas in the
PL group, age (20.83 ± 1.73 years), height (75.60 ± 3.22 cm), body mass (69.12 ± 10.46 kg)
and percent body fat (16.92 ± 5.25%).
No significant differences were observed between the CR and PL groups regarding the
composition of carbohydrate, protein, and fat in the diet during the supplementation period.
Performance
The mean changes in running performance times in CR and PL groups are shown in Table 1.
They were significantly decreased in the CR group in the 100 m (P = 0.04), but not in the 200
m (P>0.05).
TABLE 1. RUNNING PERFORMANCE TIMES DURING THE PRE AND POST-
SUPPLEMENTATION PERIOD IN THE PL (N=10) AND CR (N=10)
GROUPS. DATA PRESENTED AS MEAN ± SEM
Pre Post Pre Post
CR PL
100 m (sec) 11.96 ± 3.9 11.23 ± 1.8* 11.82 ± 3.7 11.79 ± 3.2
200 m (sec) 22.82 ± 4.9 22.47 ± 6.4 22.79 ± 5.3 22.71 ± 5.7
(CR: creatine supplementation group, PL: placebo supplementation group)
* Significant difference (P<0.05) to Pre-test
Body composition
The CR group gained significantly more body mass (0.79 ± 0.11 kg) and fat-free mass (0.54
± 0.05 kg) than the PL group (Table 2).
SAJR SPER, 32(2), 2010 Creatine supplementation, sprinting and anabolic hormones
35
TABLE 2. MEASURES OF BODY COMPOSITION IN THE PL (N=10) AND CR
(N=10) GROUPS DURING THE PRE AND POST-SUPPLEMENTATION
PERIOD. DATA PRESENTED AS MEAN ± SEM
CR group PL group
Body mass (kg)
Pre
Post
Body fat (%) #
Pre
Post
Body fat (kg) #
Pre
Post
Fat-free mass (kg) #
Pre
Post
69.16 ± 8.65
69.95 ± 9.76*
16.12 ± 4.12
15.97 ± 4.67
11.23 ± 4.51
11.48 ± 4.84
57.93 ± 5.68
58.47 ± 5.23*
69.12 ± 10.46
69.20 ± 11.12
16.92 ± 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 ± SE obtained from skinfold analyses (based on the average of two trials
and obtained on the right side)
*P < 0.05 from corresponding Pre value for the CR group only
Hormonal responses
The hormonal responses measured are presented in Table 3. No significant changes were
observed in serum GH, testosterone and cortisol concentrations from before to after-
supplementation in both groups of CR and PL (P>0.05).
TABLE 3. SERUM GROWTH HORMONE, TESTOSTERONE AND CORTISOL
CONCENTRATIONS IN THE PL (N=10) AND CR (N=10) GROUPS
DURING THE PRE AND POST-SUPPLEMENTATION PERIOD. DATA
PRESENTED AS MEAN ± SEM
Pre Post Pre Post
CR PL
Serum GH (ng/ml) 11.19 ± 2.03 11.23 ± 2.76 11.64 ± 2.26 11.67 ± 2.35
Serum Testosterone
(ng/ml)
6.21 ± 1.37 6.18 ± 1.55 6.57 ± 2.24 6.64 ± 2.85
Serum Cortisol (mg %) 19.35 ± 2.17 19.30 ± 3.57 20.17 ± 2.33 19.98 ± 3.64
DISCUSSION
It has been well established that increasing dietary availability of creatine serves to increase
total creatine and phosphocreatine concentrations in the muscle (Kreider, 2003). It is also
known that the availability of creatine and phosphocreatine play a significant role in
contributing to energy metabolism particularly during intense exercise. Theoretically,
increasing the availability of phosphocreatine would enhance cellular bioenergetics of the
SAJR SPER, 32(2), 2010 Faraji, Arazi, Sheikholeslami Vatani & Hikimi
36
phosphagen system that is involved in high-intensity exercise performance of very short
duration (Kreider, 2003), or the resynthesis of phosphocreatine during recovery (Greenhaff et
al., 1993). The results of this study indicated that creatine supplementation 20 g/day (three
times a day) for six days with no physical training decreased sprint running time (100 m) in
the 20 amateur runners assessed in this study. The present study supports the finding Skare
and Skadberg (2001), who also reported that short-term creatine supplementation (20 g/day)
decreased 100-m sprint times in runners.
Although the findings of our study support those of previous investigations (Mujika et al.
2000; Skare & Skadberg, 2001; Anomasiri et al., 2004; Hoffman et al., 2005; Kraemer et al.,
2007; Gotshalk et al., 2008) and suggest that short-term creatine supplementation can
significantly increase exercise performance, they do conflict with others (Greenhaff et al.,
1993; Mujika et al., 1996; Kinugasa et al., 2004; Mendes et al., 2004) that did not replicate
this difference. A possible explanation for the contrasting findings may be related to the
calibre of the subjects examined. It is interesting to the note that Greenhaff et al. (1993),
Mujika et al.(1996), Kinugasa et al.( 2004) and Mendes et al.( 2004) used competitive or elite
athletes as subjects whereas our subjects were amateur. Harris et al. (1992) and Greenhaff et
al. (1994) indicate that the extent of creatine uptake into the muscle is inversely related to an
individual’s initial muscle creatine content. The higher the initial intramuscular creatine
concentration, the more difficult it is to increase stores (Harris et al., 1992; Greenhaff et al.,
1994). Therefore, it is possible that our amateur runners had a greater capacity to increase
their intramuscular stores of creatine than their elite counterparts (Greenhaff et al., 1993;
Mujika et al., 1996; Kinugasa et al., 2004; Mendes et al., 2004), who may already have had
maximal intramuscular creatine concentrations. However, in this study intramuscular stores
of creatine were not measured.
Based on the role of creatine supplementation in elevating intramuscular phosphocreatine
stores and sustaining ATP production during muscle contraction (Kreider, 2003), the
expectation was that creatine supplementation would have decreased both 100 m and 200 m
performance. However, a significant improvement in mean 200 m times was not apparent.
This may have been due to the large intersubject variability and small sample size.
Participants of this study were, however, also in the collegiate amateur category. It is
therefore possible that their poor technique and coordination may have been affecting
performance results. Since the 100 m is shorter than 200 m, performance difference in 100 m
would be less. It is therefore likely that large intersubject variability and or poor technique
and coordination may have had less of an effect during the 100 m event. The small observed
changes may however be meaningful for competitive running performers.
As creatine supplementation results in a rapid increase in body mass and fat-free mass
(Rawson & Persky, 2007; Gotshalk et al., 2008), it has been hypothesised that creatine
induces muscle hypertrophy through endocrine mechanisms. Blood concentrations of GH and
testosterone stimulate muscle protein accretion (Kraemer et al., 2007) as GH stimulates
protein synthesis by activating ribosomal initiation factors and improving translational
efficiency (Bush et al., 2003). Testosterone also increases protein synthesis by binding to the
androgen receptor for the complex to become a transcription factor and thirdly by possibly
activating muscle satellite cells, which is important because gene transcription is an initial
target for the modulation of protein synthesis (Herbst & Bhasin, 2004; Olsen et al., 2006).
SAJR SPER, 32(2), 2010 Creatine supplementation, sprinting and anabolic hormones
37
No significant effects of creatine supplementation on serum GH, testosterone and cortisol
responses at rest were found. The unchanged GH and cortisol after creatine supplementation
is also consistent with other reports. For example, Op‘t Eijnde and Hespel (2001) found that
creatine supplementation (20 g/day for five days) could not alter cortisol and GH responses to
a single bout of heavy resistance exercise. Moreover, Volek et al. (1997) assessed
testosterone and cortisol immediately post-exercise (five sets of bench presses and jump
squats) in creatine (25g/day for seven days) and placebo-supplemented subjects, and found no
effect of creatine on testosterone and cortisol hormones status. Results of this study and
previous data indicate that it is unlikely that creatine supplementation is hormonally
mediated. Furthermore, it is possible that creatine supplementation may affect other protein
synthesis factors. Deldicque et al. (2005) reported that creatine supplementation (21g/day for
five days) can facilitate muscle anabolism through increase of IGF-I (30%) and IGF-II (40%)
mRNA in muscle.
Six days of creatine supplementation resulted in a small but significant increase in both body
mass (0.79 ± 0.11 kg) and fat-free mass (0.54 ± 0.05 kg). These results are similar to the
previous findings of Gotshalk et al. (2002 & 2008). A limitation of the current study was that
muscle mass and body water were not measured. Nevertheless, the acute increase in body
mass is most likely due to an increase in total body water (Ziegenfuss et al. 1998) and not an
increase in muscle protein or muscle mass (Gotshalk et al., 2008).
In conclusion, the data suggest that short-term creatine supplementation increases sprint
running performance in amateur runners. An association between creatine supplementation
and serum testosterone or decreased serum cortisol concentrations was, however, not found
and the possibility that creatine supplementation is hormonally mediated by, a systemic
change in these hormonal alterations is not supported.
ACKNOWLEDGEMENT
Thanks to Mr. Rahman Rahimi for his support throughout the course of this project. We
gratefully acknowledge the volunteers involved in this study.
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Mr. Hassan Faraji: Department of Physical Education & Sport Science, Azad University Branch of
Marivan, Marivan, Iran. Tel: +98 918 876 3846, E-mail: farajienator@gmail.com
(Subject editor: Prof. E. Peters-Futree)
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Full-text available
Creatine supplementation is a widely used and heavily studied ergogenic aid. Athletes use creatine to increase muscle mass, strength, and muscle endurance. While the performance and muscle- building effects of creatine supplementation have been well documented, the mechanisms responsible for these muscular adaptations have been less studied. Objective: The purpose of this review is to examine studies of the mechanisms underlying muscular adaptations to creatine supplementation. Data sources: PubMed and SPORTDiscus databases were searched from 1992 to 2007 using the terms creatine, creatine supplementation, creatine monohydrate, and phosphocreatine. Study selection: Studies of creatine supplementation in healthy adults were included. Data extraction: Due to the small number of studies identified, a meta-analysis was not performed. Data synthesis: Several potential mechanisms underlying muscular adaptations to creatine supplementation were identified, including: metabolic adaptations, changes in protein turnover, hormonal alterations, stabilization of lipid membranes, molecular modifications, or as a general training aid. The mechanisms with the greatest amount of support (metabolic adaptations, molecular modifications, and general training aid) may work in concert rather than independently. Conclusions: Creatine supplementation may alter skeletal muscle directly, by increased muscle glycogen and phosphocreatine, faster phosphocreatine resynthesis, increased expression of endocrine and growth factor mRNA, or indirectly, through increased training volume. Keywords: dietary supplement, creatine monohydrate, phosphocreatine, muscle, sport nutrition
Article
Creatine has become a popular nutritional supplement among athletes. Recent research has also suggested that there may be a number of potential therapeutic uses of creatine. This paper reviews the available research that has examined the potential ergogenic value of creatine supplementation on exercise performance and training adaptations. Review of the literature indicates that over 500 research studies have evaluated the effects of creatine supplementation on muscle physiology and/or exercise capacity in healthy, trained, and various diseased populations. Short-term creatine supplementation (e.g. 20 g/day for 5–7 days) has typically been reported to increase total creatine content by 10–30% and phosphocreatine stores by 10–40%. Of the approximately 300 studies that have evaluated the potential ergogenic value of creatine supplementation, about 70% of these studies report statistically significant results while remaining studies generally report non-significant gains in performance. No study reports a statistically significant ergolytic effect. For example, short-term creatine supplementation has been reported to improve maximal power/strength (5–15%), work performed during sets of maximal effort muscle contractions (5–15%), single-effort sprint performance (1–5%), and work performed during repetitive sprint performance (5–15%). Moreover, creatine supplementation during training has been reported to promote significantly greater gains in strength, fat free mass, and performance primarily of high intensity exercise tasks. Although not all studies report significant results, the preponderance of scientific evidence indicates that creatine supplementation appears to be a generally effective nutritional ergogenic aid for a variety of exercise tasks in a number of athletic and clinical populations.
Article
This study investigated the influence of oral creatine monohydrate supplementation on hormone responses to high-intensity resistance exercise in 13 healthy, normally active men. Subjects were randomly assigned in double-blind fashion to either a creatine or placebo group. Both groups performed bench press and jump squat exercise protocols before (T1) and after (T1) ingesting either 25 g creatine monohydrate or placebo per day for 7 days. Blood samples were obtained pre- and 5 min postexercise to determine serum lactate, testosterone, and cortisol concentrations. Creatine ingestion resulted in a significant (p < 0.05) increase in body mass but no changes in skinfold thickness. Serum lactate concentrations were significantly higher at 5 min postexercise in both groups compared to resting values. From T1 to T2 there were no significant differences in postexercise lactate concentration during both exercise protocols in the placebo group, but the creatine group had significantly higher lactate concentrations after the bench press and a trend toward lower concentrations during the jump squat at T2. There were significant increases in testosterone concentration postexercise after the jump squat, but not the bench press, for both groups; 5-min postexercise cortisol concentrations did not differ significantly from preexercise values for both groups for either protocol. Creatine supplementation may increase body mass; however, test-osterone and cortisol may not mediate this initial effect. (C) 1997 National Strength and Conditioning Association
Article
Simple voltammetric determination of thiodiglycolic acid (TDGA) offers the possibility to follow individual deviations in metabolism of thiocompounds and one-carbon (1c) and two-carbon (2c) units, which take part in endogenous synthesis of creatine (CR). In three groups of young men the levels of TDGA in urine were followed after application of CR given as food supplement in 5 g daily doses. In the first group (7 men) it was found that the level of TDGA increased independently of the day time of application of CR. In the second group (9 men) the level of TDGA increased within an interval of 3–8.5 h after CR application and then dropped during 2 h to the normal level (20 mg L−1). In the third group (11 men), in 4 days’ study the effects of CR were compared in alternation to vitamin B12. Vitamin B12 was given in the evening of the 1st and 3rd day and CR in the morning of the 3rd and 4th day. CR increased the excretion of TDGA in all men, while B12 only in four men independently of CR application.
Article
1. The present study was undertaken to test whether creatine given as a supplement to normal subjects was absorbed, and if continued resulted in an increase in the total creatine pool in muscle. An additional effect of exercise upon uptake into muscle was also investigated. 2. Low doses (1 g of creatine monohydrate or less in water) produced only a modest rise in the plasma creatine concentration, whereas 5 g resulted in a mean peak after 1 h of 795 (sd 104) μmol/l in three subjects weighing 76–87 kg. Repeated dosing with 5 g every 2 h sustained the plasma concentration at around 1000 μmol/l. A single 5 g dose corresponds to the creatine content of 1.1 kg of fresh, uncooked steak. 3. Supplementation with 5 g of creatine monohydrate, four or six times a day for 2 or more days resulted in a significant increase in the total creatine content of the quadriceps femoris muscle measured in 17 subjects. This was greatest in subjects with a low initial total creatine content and the effect was to raise the content in these subjects closer to the upper limit of the normal range. In some the increase was as much as 50%. 4. Uptake into muscle was greatest during the first 2 days of supplementation accounting for 32% of the dose administered in three subjects receiving 6 × 5 g of creatine monohydrate/day. In these subjects renal excretion was 40, 61 and 68% of the creatine dose over the first 3 days. Approximately 20% or more of the creatine taken up was measured as phosphocreatine. No changes were apparent in the muscle ATP content. 5. No side effects of creatine supplementation were noted. 6. One hour of hard exercise per day using one leg augmented the increase in the total creatine content of the exercised leg, but had no effect in the collateral. In these subjects the mean total creatine content increased from 118.1 (sd 3.0) mmol/kg dry muscle before supplementation to 148.5 (sd 5.2) in the control leg, and to 162.2 (sd 12.5) in the exercised leg. Supplementation and exercise resulted in a total creatine content in one subject of 182.8 mmol/kg dry muscle, of which 112.0 mmol/kg dry muscle was in the form of phosphocreatine.
Article
Anthropometry is the method of choice for estimating body composition in the clinical setting. The method can be accurate, and requires little time, space, equipment, or financial outlay. Although used extensively in epidemiological research, height/weight indices are not as accurate as skinfold and circumference measures for estimating body composition. The validity of estimating body density is enhanced by using a combination of skin-fold and circumference measures in a multiple-regression model. Some recently developed generalized equations may have a broader application for use in varied populations than several population-specific equations. The newer equations take into account the potential change in ratio of internal to external fat and bone density with age, and the nonlinear relationship between skinfold fat and body density. The validity of using skinfolds for estimating body density can be significantly affected by caliper selection and measurement procedures. Inter-observer errors appear to be the most problematic, with improper skinfold site selection causing the greatest variation among observers. To improve the validity of the anthropometric technique for use in the clinical setting, more precise standards and description of methods need to be developed.
Article
Biopsy samples were obtained from the vastus lateralis muscle of eight subjects after 0, 20, 60, and 120 s of recovery from intense electrically evoked isometric contraction. Later (10 days), the same procedures were performed using the other leg, but subjects ingested 20 g creatine (Cr)/day for the preceding 5 days. Muscle ATP, phosphocreatine (PCr), free Cr, and lactate concentrations were measured, and total Cr was calculated as the sum of PCr and free Cr concentrations. In five of the eight subjects, Cr ingestion substantially increased muscle total Cr concentration (mean 29 +/- 3 mmol/kg dry matter, 25 +/- 3%; range 19-35 mmol/kg dry matter, 15-32%) and PCr resynthesis during recovery (mean 19 +/- 4 mmol/kg dry matter, 35 +/- 6%; range 11-28 mmol/kg dry matter, 23-53%). In the remaining three subjects, Cr ingestion had little effect on muscle total Cr concentration, producing increases of 8-9 mmol/kg dry matter (5-7%), and did not increase PCr resynthesis. The data suggest that a dietary-induced increase in muscle total Cr concentration can increase PCr resynthesis during the 2nd min of recovery from intense contraction.