| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Nuclear Magnetic Resonance Center, Department of Medical Biochemistry and Genetics, Panum Institute, University of Copenhagen, and Copenhagen Muscle Research Center, DK-2100 Copenhagen, Denmark; and Group of Biomedical Applications of Magnetic Resonance, Department of Biochemistry and Molecular Biology, University Autonoma of Barcelona, 08193 Bellaterra, Spain
 |
ABSTRACT |
|---|
 TOP
 ABSTRACT
 INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
The purpose of this study was to examine with 31P-magnetic resonance spectroscopy energy metabolism during repeated plantar flexion isometric exercise (Ex-1-Ex-4) at 32 ± 1 and 79 ± 4% of maximal voluntary contraction (MVC) before and during a creatine (Cr) feeding period of 5 g/day for 11 days. Eight trained male subjects participated in the study. ATP was unchanged with Cr supplementation at rest and during exercise at both intensities. Resting muscle phosphocreatine (PCr) increased (P < 0.05) from 18.3 ± 0.9 (before) to 19.6 ± 1.0 mmol/kg wet wt after 9 days. At 79% MVC, PCr used, Pi accumulated, and pH at the end of Ex-1-Ex-4 were similar after 4 and 11 days of Cr supplementation. In contrast, PCr utilization and Pi accumulation were lower and pH was higher for exercise at 32% MVC with Cr supplementation, suggesting aerobic resynthesis of PCr was more rapid during exercise. These results suggest that elevating muscle Cr enhances oxidative phosphorylation during mild isometric exercise, where it is expected that oxygen delivery matches demands and predominantly slow-twitch motor units are recruited.
nuclear magnetic resonance; oxidative phosphorylation; skeletal muscle; phosphocreatine; inorganic phosphate
| |
INTRODUCTION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
RECENT STUDIES (4, 19, 21, 22, 43) have demonstrated that human muscles retain ~10-35% of the 20-30 g of creatine (Cr) per day supplemented to the habitual diet for 3-6 days, and a recent report showed that 14 days of Cr feeding (3 g/day) raised the total Cr storage in human muscle as much as ingesting doses of 20 g/day for 6 days (22). The enlarged intramuscular total Cr storage after Cr supplementation has been associated with increments in the work performed in one and repeated bouts of intense muscle contractions (3, 4, 9, 10), although no alteration of performance has been observed in some cases (11, 33, 43). The improved muscle performance during repeated exercise after Cr supplementation was suggested to be due to a higher phosphocreatine (PCr) concentration and to an accelerated rate of PCr resynthesis during the recovery periods (4, 10, 19), and there is recent evidence that muscle mass might increase during Cr feeding, which might also play a role in the improvements in muscle work (42, 45). However, a role for Cr as a controller of oxidative phosphorylation, enabling higher rates of oxidative metabolism during muscle contraction, has been basically ignored.
If Cr enhances muscle oxidative phosphorylation during recovery from ischemic exercise, as suggested by the results of Greenhaff et al. (19), enhancement of PCr resynthesis should also occur during the exercise periods after Cr supplementation unless by some unexplained mechanism this physiological event can only occur during recovery from muscular contraction. One important condition for the enhancement of PCr resynthesis during exercise is that there is no limitation of oxygen supply, because the resynthesis of PCr in human muscle appears to occur solely in the presence of oxygen (36). Also, control of oxidative phosphorylation in slow-twitch (ST) and fast-twitch (FT) fibers might be different (25, 31, 32). Recent reports have shown that ADP is restricted in the outer mitochondrial membrane in cardiac myocytes and ST skeletal muscle fibers (37) and that Cr addition enhanced aerobic phosphorylation only in these fibers (26, 46). Therefore, after Cr supplementation, enhancement of PCr resynthesis during aerobic exercise should result in a lesser fall in muscle PCr. These differences should be detected in human muscle during protocols of different recruitment pattern and oxygen availability.
In the present study, the effect of a relatively low Cr dosage (5 g/day) on muscle metabolism was examined with 31P-magnetic resonance spectroscopy (31P-MRS) at rest, during four bouts of isometric plantar flexion at light [32% maximal voluntary contraction (MVC)] and high (79% MVC) intensities, and during recovery after each bout. The 79% MVC protocol was expected to have more restriction of oxygen supply and to recruit relatively fewer ST fibers than would the other because of the higher intensity of the isometric contraction. It was hypothesized that aerobic phosphorylation during the exercise periods would be enhanced after Cr supplementation during light but not intense exercise. The results support this hypothesis, as evidenced by a smaller net utilization of PCr during exercise, and suggest that Cr supplementation enhanced aerobic phosphorylation for light exercise where oxygen delivery could match demand in ST fibers being recruited.
| |
METHODS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Subjects. Eight trained male subjects ranging in age from 23 to 30 yr participated in this study. Subjects were engaged in endurance training at least three times a week, and one of them competed in elite handball. The study was approved by the Ethics Committee of the University of Copenhagen. Informed consent was obtained from all subjects after they received a detailed explanation of the procedures and the risks and discomforts of the experiment.
Experimental design. In a preliminary visit to introduce the subjects to the experimental protocols and setup, three maximal voluntary isometric plantar flexion contractions (MVC) of 3-s duration separated by 2 min were performed. The highest value of the three trials was taken as the MVC. After being accustomed to the equipment set up (5), subjects came to the laboratory on several occasions to complete four exercise bouts (Ex-1-Ex-4) of 3-min 20-s duration separated by 4 min of rest. Subjects warmed up for 5 min at 10% MVC followed by 10 min of rest before performing the repeated exercise bouts. The intensity of the exercise was adjusted accordingly in subsequent visits until the target intensity was identified. The aim was for the subjects to endure four exercise bouts, developing the same tension in each bout and reaching near exhaustion by the end of the fourth bout so that they were unable to complete a fifth bout. Similar procedures were followed for the higher intensity protocol, which consisted of four exercise bouts of 40-s duration separated by 2 min of rest. These procedures required at least two to three visits for each protocol.
Once the intensities were identified for each subject, two additional visits before the Cr supplementation period (Bas) were scheduled for each protocol to test the reproducibility of measurements and to rule out a training effect. The two protocols were performed alternatively on separate days with 1-3 days in between and with 4-6 days between the two tests for each protocol. The average load for the high-intensity protocol was 79 ± 4% MVC and that for the low-intensity protocol was 32 ± 1% MVC. During the Cr supplementation period, the 79% MVC protocol was performed on days 4 (Cr-4) and 11 (Cr-11), and the 32% MVC protocol was performed on day 9 (Cr-9). During the exercise bouts, force was recorded by a calibrated strain gauge. Subjects kept force at target level by watching the strain-gauge readout and by continuous feedback from the experimenter. The same duration and tension for each exercise bout were applied, thus keeping the total time × tension integral constant before and after Cr supplementation in both protocols. During the Cr supplementation period, subjects were given 5 g/day of Cr monohydrate (Ergomax, Copenhagen, Denmark) for 11 days. The subjects were requested to ingest the daily dose in three doses after breakfast (1 g), lunch (2 g), and dinner (2 g) dissolved in 300 ml of warm water.MRS. Subjects positioned their dominant leg in the ergometer in a 2.9-T, 26-cm-bore-diameter, and 80-cm-bore-length Magnex magnet that was interfaced to an Otsuka VivoSpec spectrometer. A two-turn inductively driven surface radio frequency coil, 39 mm in diameter, was located over the belly of the gastrocnemius muscle. The area of the muscle described by the circumference of the surface coil was marked, and the distance from the fossa poplitea was measured the first day. In subsequent visits, the coil was placed exactly at the same location. Shimming was performed by preshimming on the proton signal from muscle water and fine shimming on the PCr signal. Spectra of phosphorus containing metabolites were obtained at 49.85 MHz. For spectra acquisition, a pulse width of 60 ms (90°) with an interpulse delay of 5 s was employed. Data were collected in 2,048 data points and with a spectral width of 10 kHz. Four free induction decays (FIDs) were collected for each spectrum during exercise at 32% MVC and only one FID for exercise at 79% MVC. During the recovery from the 79% MVC protocol, a spectrum consisted of the sum of two FIDs. Before Fourier transformation, the data were multiplied by 5-Hz exponential line broadening. Baseline correction was obtained by convolution difference. Integration of the peak areas was performed by a least-squares fitting routine assuming a Lorentzian line shape and then corrected for partial saturation. Saturation factors were obtained on all subjects at rest with an interpulse delay of 25 s. A total of nine saturation factor measurements were obtained for each subject. The average saturation factor for Pi, PCr, and ATP was 1.25 ± 0.02, 1.37 ± 0.02, and 1.14 ± 0.01, respectively.
The unsaturated areas for all metabolites were converted to concentrations by assuming average integrated ATP signal for all subjects during the baseline period to correspond to a resting concentration of 5.5 mmol/kg wet wt. Intracellular pH during the exercise periods was calculated from the chemical shift difference of the Pi peak with respect to the PCr peak (2). The parameters for the time course of PCr resynthesis were determined by fitting the points to a monoexponential growth curve.Statistics. Values are expressed as means ± SE. Differences between results of the two protocols during the first and second visits of the Bas and between before and after Cr for each protocol were analyzed by repeated-measures analysis of variance. A post hoc Scheffé's F-test was used to analyze any significant difference. Differences were considered significant at the 5% probability level. Because no significant differences between the rates of PCr breakdown and recovery, Pi accumulation, and pH changes were found between the two baseline visits for either of the protocols, the average of all the values for all parameters for these two visits was taken for comparison with the values during the supplementation period.
| |
RESULTS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Resting muscle metabolite concentrations.
Muscle ATP and Pi remained unchanged during the
supplementation period (Table 1). Average
resting muscle PCr during baseline increased (P < 0.05 and
P < 0.01, respectively) after the 9th and 11th days. Assuming
a PCr-to-total Cr (TCr) ratio of 0.65 and 0.61 before and after the
supplementation period, respectively (values obtained from 84 subjects
of Refs. 3, 9, 14, 24; assuming 77% muscle water), the free Cr was
calculated to be 9.9 ± 0.5 mmol/wet wt at Bas and 12.5 ± 0.6 and 12.4 ± 0.6 mmol/kg wet wt after Cr-9 and Cr-11, respectively.
The calculated increase in TCr amounted to 14% of the resting value.
|
Muscle metabolism.
The ATP changes during exercise were not significantly altered by Cr
supplementation in either of the protocols. The dynamic changes of PCr
during the exercise periods during the 79% MVC protocol are shown in
Fig. 1. The net PCr utilization during
Ex-1-Ex-4 (11.9 ± 0.8, 13.9 ± 1.1, 14.9 ± 1.3, and 15.9 ± 1.3 mmol/kg wet wt, respectively) did not change after Cr-4 and Cr-11.
However, during the 32% MVC protocol, the net PCr breakdown during
Ex-1 and Ex-2 (4.6 ± 0.5 and 7.7 ± 0.8 mmol/kg wet wt,
respectively) was significantly lower (P < 0.05 and P < 0.01, respectively) after Cr-9 (3.5 ± 0.6 and 5.7 ± 0.8 mmol/kg
wet wt, respectively; Fig. 2). Also, during
Ex-3, the net muscle PCr utilized was lower between 50 s and the end of
exercise after Cr-9, although the differences were only significant at
72.5 (P < 0.05), 92.5 (P < 0.05), and 172.5 s
(P < 0.05), and there was a strong tendency at 52.5 (P = 0.05) and 192.5 s (P = 0.06) into the exercise.
During Ex-4, PCr used was also significantly lower at 92.5 (P < 0.05) and 112.5 s (P < 0.05). After this time, the net
PCr utilized was not significantly lower after Cr-9 compared with Bas.
During the 79% protocol, the half time of PCr resynthesis was
lengthened (P < 0.05) after Cr-11 compared with Bas during
recovery from Ex-1 and Ex-4, whereas it was lengthened (P < 0.05) during recovery from Ex-2 after Cr supplementation during the
32% MVC protocol (Tables 2 and
3).
|
|
|
|
|
|
|
|
1 · s1 after Cr-11,
and during the last 20 s of contraction it was 0.171 ± 0.028 and
0.204 ± 0.034 mmol · kg wet
wt1 · s1 in Bas and
Cr-11, respectively. H+ was not significantly changed (Fig.
9A).
|
|
|
1 · s1) was
also lower (P < 0.01) after Cr-9 (0.016 ± 0.006 mmol · kg wet
wt1 · s1; Fig.
8B). The rate of Pi accumulation from ~120 s to
the end of exercise tended to be lower (P = 0.06) after Cr-9
(0.048 ± 0.006 vs. 0.033 ± 0.006 mmol · kg wet
wt1 · s1). The
rates of H+ buffered (0-50 s) and accumulation
(50-120 s) to ~120 s did not change after Cr-9, but the rate of
H+ accumulation from 120 s until the end of contraction was
significantly lower (P < 0.01) after Cr-9 (0.41 ± 0.08 vs.
0.22 ± 0.09 nM/s; Fig. 9B).
| |
DISCUSSION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
The main aims of this study were to investigate the effects of Cr supplementation at a daily dose of 5 g on resting muscle metabolites and muscle energy metabolism during repeated exercise of different intensities. It was hypothesized that an effect of Cr on aerobic metabolism would occur during the exercise periods for light but not for heavy isometric exercise. The results support this hypothesis, as evidenced by the lower PCr breakdown, Pi accumulation, and pH drop in the lower intensity protocol after Cr feeding.
During the Cr supplementation period, the ATP values remained unchanged, which is in agreement with the results of other studies (4, 10, 13, 19, 21, 22, 43). Despite the comparatively low daily dose of Cr given in the present study, intramuscular PCr increased 1.3 mmol/kg wet wt after 9 days of Cr feeding. It is also very likely that in this study the muscle free Cr increased more than PCr did, as has been demonstrated in all the recent studies (4, 10, 13, 19, 21, 22, 43). Calculations showed that, after Cr supplementation, ~2.5 mmol/kg wet wt of free Cr were deposited in the muscle examined. Assuming 30 kg muscle mass and the same uptake in all muscles as occurred in the gastrocnemius, ~16 g of Cr would be retained by the 11th day, which corresponded to 29% of the dose given. Studies have shown that 10-35% of the Cr supplement is retained for doses ranging from 3 to 30 g during periods of up to 44 days (4, 10, 13, 19, 21, 22, 35, 43). It is clear from these experiments that Cr entry into and retention by muscle can be accomplished by different regimens, but a large part of the Cr supplement is lost. Human muscle cells take up Cr from blood by a Na+-dependent and Na+-independent specific transport process (27). The Na+-dependent transport is downregulated by physiological plasma Cr (27), which might be a limitation when very high doses are given for a prolonged period. Insulin (23), exercise (21), vitamin E (15), and high-carbohydrate feeding have been shown to have a positive influence on the uptake of Cr in muscle (16, 17). The subjects' diet and activity were not recorded in the present experiment, but they were requested to keep the same activity and food intake patterns during the course of the study. Nevertheless, the significant gain in muscle PCr of ~7% indicates the supplementation was successful.
The effect of Cr supplementation on muscle energy metabolism was investigated noninvasively during two protocols of repeated isometric contraction: one at high intensity (79% of MVC) and another at low intensity (32% of MVC). During high-intensity isometric contraction, a large number of fibers (both ST and FT) must be recruited, and above 50-70% of MVC, a large reduction in blood flow during exercise is expected. For instance, during contraction of the quadriceps at 50% MVC, lower blood flow and muscle oxygen uptake were observed compared with contraction at 25% MVC (14). Furthermore, endurance time of the quadriceps muscle during contraction at 67% of MVC was the same with or without circulatory occlusion (12), indicating that above ~67% MVC local ischemia occurs. Because PCr resynthesis is dependent on adequate blood flow and oxygen delivery (36), Cr supplementation would not be expected to enhance PCr resynthesis during exercise at 79% MVC where such a limitation is likely to occur. The findings at this high intensity are consistent with this hypothesis. That is, the PCr decrease, Pi accumulation, and pH change during the four exercise bouts at Bas were not different from those after Cr-4 and Cr-11. In contrast, the 32% MVC protocol recruits a fewer number of fibers, causing significantly less restriction of blood flow and muscle oxygenation (14). Supplementation, in this case, is expected to enhance the resynthesis of PCr, thereby reducing the PCr loss, Pi accumulation, and pH fall during light exercise as found in the present study.
It has been shown that the rate of PCr degradation of rat and human muscle follows a monoexponential decay during submaximal isotonic exercise of different intensities (28, 29). In the present study, PCr degradation during isometric exercise at 32% MVC was more complex. Up to ~120 s of exercise, the PCr decline followed a monoexponential pattern, but from then on its decay was linear. Furthermore, the data showed a progressive tendency for the monoexponential decay to be linear with the number of bouts. Cr supplementation tended to attenuate this pattern. The explanation for this complex response currently is unknown. A possibility is a progressive change in the type and number of muscle fibers recruited during light isometric exercise as fatigue develops. At low exercise intensities, there is an orderly recruitment of ST, FTa, and FTb fibers as time progresses to fatigue (47). The recruitment of a larger number of FT fibers with time and in repeated bouts could have produced a progressive limitations in blood flow and oxygen delivery to working muscle, thereby changing PCr kinetics from monoexponential to a linear dynamic. Experiments on isolated mitochondria have shown that PCr decreases linearly when mitochondrial respiration exhausts the oxygen available and oxidative phosphorylation becomes oxygen limited (20). Alterations in H+ per se do not appear to be involved. The finding that Cr supplementation affected the net PCr utilization and Pi accumulation but did not affect pH during the monoexponential decay period excludes any effect of H+ on the kinetics of PCr during this time. Furthermore, H+ accumulation was lower from 120 to 200 s after Cr supplementation, suggesting that the rate of H+ production through anaerobic glycolysis was lower, but the PCr degradation rate was not changed by supplementation during this later period of low-intensity exercise. In other studies, Balsom et al. (4) found a lower muscle lactate accumulation at the end of repeated 6-s bouts of supramaximal cycling, whereas Febbraio et al. (13) found no change in glycogen degradation or lactate accumulation after five 1-min bouts after Cr supplementation. These controversial findings would need to be clarified in future research. Thus it is proposed that, whereas the oxygen delivery was not impeded and a larger relative proportion of ST fibers was recruited, oxidative phosphorylation during the exercise periods was likely enhanced after Cr supplementation.
Contrary to the present suggestion of an increment in oxidative phosphorylation during the exercise periods, Balsom et al. (4) proposed that the lower net PCr breakdown at the end of repeated bouts of maximal exercise was due to higher resynthesis of PCr during the recovery periods as demonstrated by Greenhaff et al. (19) during recovery from ischemic exercise. However, other results obtained in Greenhaff's laboratory with 31P-MRS and biochemical analysis have shown that the amount of PCr resynthesized during recovery from ischemic and nonischemic exercise in tibialis and vastus lateralis, respectively, did not change after Cr supplementation (10, 18), whereas no explanation for the discrepant results has been given (10). Also, Balsom et al. (4) measured PCr from muscle biopsies obtained only before the first bout and after the fifth bout, and the recovery periods between exercise bouts were 30 s, whereas the results of Greenhaff et al. (19) showed no change in the rate of PCr resynthesis during the first minute of recovery. A recent study showed that the amount of PCr resynthesized during 2 min of recovery from a 20-s sprint was not affected but that a significant relationship was found between the percent increase in TCr and the percent change in PCr after 2 min of recovery after Cr supplementation (43). If the amount of PCr is increased after Cr supplementation only after ~2 min of recovery from exercise, the half time of PCr resynthesis would be lengthened. Indeed, estimation of the half time of PCr resynthesis from the PCr changes in vastus lateralis muscle of the responders to Cr in the study of Greenhaff et al. gave values of ~28 s before Cr supplementation and of ~40 s after Cr supplementation. Slower resynthesis rates of PCr in tibialis muscle after Cr supplementation have also been shown with 31P-MRS during 6-min recovery from different workloads (24). In the present study, the results of the average of the four recovery bouts indicate that PCr resynthesis might be enhanced during the latter part of the recovery from high-intensity isometric exercise in agreement with the results of Greenhaff et al. during recovery from ischemic exercise. The lengthening of the PCr resynthesis rate cannot be explained by an effect of pH, because the end-exercise pH was not different from resting values in this protocol. In support of the absence of an effect of pH on PCr resynthesis rate is that, during the 32% MVC protocol, the half time of PCr resynthesis was not different with repeated bouts of exercise despite a progressive lower end-exercise pH. Greenhaff et al. also discarded this possibility when they observed higher muscle lactate at the end of exercise after Cr loading. To explain the enhancement of PCr resynthesis after only 2 min of recovery, Greenhaff et al. (19) argued that, immediately after maximal exercise, free Cr is above the Michaelis-Menten constant (Km) of creatine kinase (CK) for Cr and that consequently a higher rate of PCr resynthesis is not expected after Cr supplementation. They reasoned that small changes in free Cr concentration as the free Cr starts decreasing toward the Km value can play a larger role in the rate of PCr resynthesis. Also, if the Cr that is taken up after supplementation and that is released from the breakdown of PCr has much greater access to the site of phosphorylation than does any other free Cr (39), any effect of free Cr on oxidative phosphorylation during the recovery period was more likely to be present during the 79% MVC protocol in the present study because the Cr released from PCr degradation was not different after Cr supplementation. On the other hand, the Cr released from PCr breakdown during exercise in the 32% MVC protocol was likely lower after Cr supplementation. Therefore, the total free Cr at the end of exercise in this protocol was probably not different compared with before supplementation. Following the previous argument of fiber-type recruitment during exercise and the arguments of Greenhaff et al. and Savabi (39), it is also possible to reconcile why Cr might have affected oxidative metabolism only during the exercise period of the 32% MVC protocol and during the recovery of the 79% MVC protocol in the present study, as evidenced by the pooled data of the four exercise and recovery periods.
The mechanism by which oxidative phosphorylation in human muscle might have been increased after Cr supplementation might not differ from that of animal muscle. The enhancement of respiration by Cr in muscle was first observed by Thunberg and supported by findings of Katz (in Ref. 8) and was strengthened by the observations of Belitser and Tsybakova (6). The phenomenon was proposed to occur via CK in the mitochondrial intermembrane space (Mit-CK) and a Cr-PCr shuttle, which, by some mechanism yet undiscovered, carried Cr to mitochondria and provided PCr to myofibrils, sarcolemma, and sarcoplasmic reticulum where the energy is needed during muscle contraction (7, 8, 38). Later investigations on skeletal muscle cell cultures and cardiomyocytes also confirmed that additional Cr increased the rate of oxidative phosphorylation and highlighted the role of the CK system in the transport of intracellular energy from mitochondria to myofibrils and other sites of energy utilization (8, 37, 38, 41). In cardiomyocytes, the higher respiration rates and higher rates of PCr production observed after Cr addition were suggested to be caused by an amplification of the sensitivity of respiration to ADP (Km: 300 µM before Cr vs. 36 µM after Cr) (40) because of the coupling of Mit-CK, adenine nucleotide translocase, and oxidative phosphorylation (37). In skeletal muscle, differences in regulation of oxygen consumption in FT and ST muscle were first suggested by Meyer et al. (31) and Kushmerick et al. (25). Meyer et al. (31) proposed that perhaps the mitochondria in the two fiber types were not the same. It was latter reported that ADP was restricted in the outer mitochondrial membrane in cardiac myocytes and ST skeletal muscle fibers (37) and that this restriction could be the explanation for the controlling role of Cr on oxidative phosphorylation in these fibers and not in FT fibers (26, 46). Meyer and Foley (32) have also reported differences in the regulation of oxygen consumption in ST and FT fibers. Moreover, the Mit-CK of the human gastrocnemius muscle has been shown to qualitatively and kinetically resemble that of heart muscle (1, 40). The M-CK activity is also higher in human trained vs. untrained muscle (1) and higher in ST compared with FT muscle (48). Therefore, there is a higher likelihood to observe an effect of Cr on oxidative phosphorylation during exercise demanding larger relative involvement of ST fibres in highly active humans. The present results show that this was likely the case. In contrast, after assuming that the increase in TCr concentration after Cr supplementation was larger in FT fibers, Casey et al. (10) proposed increased mitochondrial ATP production in this fiber type (10). However, their own data do not support larger increases in TCr concentration in FT fibers after Cr supplementation (Table 2 in Ref. 10). Also, results from animal muscle showed that depletion of up to 90% of TCr had no effect on aerobic metabolism in FT fibers (30), and it was suggested that in FT fibers the CK system acts as a simple buffer of adenine nucleotide levels (29, 30). Furthermore, in support of the contention that the effect of Cr on oxidative metabolism is confined to the ST fibers are the results of a recent report that showed a correlation between the percentage of ST fibers and the enhancement of oxidative phosphorylation after Cr was added to human skinned fibers obtained after exercise (44). An additional or sinergistic possibility is the proposed regulation of PCr/Cr on AMP-activated protein kinase (AMPK) as the control mechanism of CK in muscle (34). According to this novel mechanism, during the 32% MVC protocol a larger decrease in PCr/Cr during exercise after Cr feeding would have inhibited PCr breakdown and enhanced oxidation of fatty acids by the dual control of AMPK inhibiting MM CK isoform and acetyl-CoA carboxylase, the latter eventually causing a drop in malonyl-CoA relieving the inhibition of carnitine palmitoyltransferase I. The possible ischemic conditions during the exercise periods of the 79% MVC protocol would have prevented oxidative phosphorylation from taking place. However, because PCr/Cr was lower after Cr feeding, particularly during the latter phase of recovery, this might have enhanced the oxidation of fatty acids and therefore increase the rate of PCr resynthesis. Possible differences in the control of AMPK in ST and FT fibers by PCr/Cr remain to be discovered, which might add to explain further the role of Cr in human muscle energy metabolism.
In conclusion, the results of this study demonstrate that adding a daily dose of 5 g Cr to the habitual diet increases muscle PCr in 9 days. Net muscle PCr utilization, Pi accumulation, and pH drop were reduced during repeated bouts of relative low-intensity exercise leading to exhaustion after Cr supplementation, indicating that muscle oxidative phosphorylation during contraction is increased by Cr supplementation. This did not occur at high-intensity exercise. This difference is likely the result of better matching of oxygen delivery with demand and greater recruitment of ST fibers.
| |
ACKNOWLEDGEMENTS |
|---|
During the completion of this research project, J. Rico-Sanz was partly funded by the Copenhagen Muscle Research Center, and by the Spanish Ministry of Education and Culture under project SAF96-0147 of the Spanish Interministerial Commission of Science and Technology.
| |
FOOTNOTES |
|---|
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: J. Rico-Sanz, Group of Biomedical Applications of Magnetic Resonance, Dept. of Biochemistry and Molecular Biology, Facultat de Ciencies, Universitat Autonoma de Barcelona, 08193 Bellaterra, Barcelona, Spain (E-mail: j.rico-sanz{at}proton.uab.es).
Received 2 October 1998; accepted in final form 28 October 1999.
| |
REFERENCES |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
1.
Apple, F. S.,
and
Tesch P. A.
CK and LD isozymes in human single muscle fibers in trained athletes.
J. Appl. Physiol.
66:
2717-2720,
1989
2.
Arnold, D. L.,
Matthews P. M.,
and
Radda G. K.
Metabolic recovery after exercise and the assessment of mitochondrial function in vivo in human skeletal muscle by means of 31P-NMR.
Magn. Reson. Med.
1:
307-315,
1984[Web of Science][Medline].
3.
Balsom, P. D.,
Ekblom B.,
Söderlund K.,
Sjödin B.,
and
Hultman E.
Creatine supplementation and dynamic high-intensity intermittent exercise.
Scand. J. Med. Sci. Sports
3:
143-149,
1993.
4.
Balsom, P. D.,
Söderlund K.,
Sjödin B.,
and
Ekblom B.
Skeletal muscle metabolism during short duration high intensity exercise: influence of creatine supplementation.
Acta Physiol. Scand.
154:
303-310,
1995[Web of Science][Medline].
5.
Bangsbo, J.,
Johansen L.,
Quistorff B.,
and
Saltin B.
NMR and analytic biochemical evaluation of CrP and nucleotides in the human calf during muscle contraction.
J. Appl. Physiol.
74:
2034-2039,
1993
6.
Belitser, V. A.,
and
Tsybakova E. T.
The mechanism of phosphorylation associated with respiration.
Biochimiya
4:
516-534,
1939.
7.
Bessman, S. P.,
and
Fonyo A.
The possible role of mitochondrial bound creatine kinase in regulation of mitochondrial respiration.
Biochem. Biophys. Res. Commun.
22:
597-602,
1966[Web of Science][Medline].
8.
Bessman, S. P.,
and
Geiger P. J.
Transport of energy in muscle: the phosphorylcreatine shuttle.
Science
211:
448-452,
1981
9.
Birch, R.,
Noble D.,
and
Greenhaff P. L.
The influence of dietary creatine supplementation on performance during repeated bouts of maximal isokinetic cycling in man.
Eur. J. Appl. Physiol.
69:
268-270,
1994[Web of Science].
10.
Casey, A.,
Constantin-Teodosiu D.,
Howell S.,
Hultman E.,
and
Greenhaff P. L.
Creatine ingestion favorably affects performance and muscle metabolism during maximal exercise in humans.
Am. J. Physiol. Endocrinol. Metab.
271:
E31-E37,
1996
11.
Cooke, W. H.,
Grandjean P. W.,
and
Barnes W. S.
Effect of oral creatine supplementation on power output and fatigue during bicycle ergometry.
J. Appl. Physiol.
78:
670-673,
1995
12.
Edwards, R. H. T.,
Nordesjö L. O.,
Koh D.,
Harris R. C.,
and
Hultman E.
Isometric exercise
factors influencing endurance and fatigue.
In: Muscle Metabolism During Exercise: Advances in Experimental Medicine and Biology, edited by Pernow B.,
and Saltin B.. New York: Plenum, 1971, vol. II, p. 357-360.
13.
Febbraio, M. A.,
Flanagan T. R.,
Snow R. J.,
Zhao S.,
and
Carey M. F.
Effect of creatine supplementation on intramuscular TCr, metabolism and performance during intermittent, supramaximal exercise in humans.
Acta Physiol. Scand.
155:
387-395,
1995[Web of Science][Medline].
14.
Gaffney, F. A.,
Sjøgaard G.,
and
Saltin B.
Local and central hemodynamic response to sustained static contraction in man.
Acta Physiol. Scand.
138:
249-258,
1990[Web of Science][Medline].
15.
Gerber, G. B.,
Gerber G.,
Koszalka T. R.,
and
Emmel V. M.
Creatine metabolism in vitamin E deficiency in the rat.
Am. J. Physiol.
202:
453-460,
1962.
16.
Green, A. L.,
Hultman E.,
Macdonald I. A.,
Sewell D. A.,
and
Greenhaff P. L.
Carbohydrate ingestion augments skeletal muscle creatine accumulation during creatine supplementation in humans.
Am. J. Physiol. Endocrinol. Metab.
271:
E281-E286,
1996.
17.
Green, A. L.,
Simpson E. J.,
Littlewood J. J.,
Macdonald I. A.,
and
Greenhaff P. L.
Carbohydrate ingestion augments creatine retention during creatine feeding in humans.
Acta Physiol. Scand.
158:
195-202,
1996[Web of Science][Medline].
18.
Greenhaff, P. L.,
Bodin K.,
Harris R.,
Hultman E.,
Jones D. A.,
Mcintyre D. B.,
Söderlund K.,
and
Turner D. L.
The influence of oral creatine supplementation on muscle phosphocreatine resynthesis following intense contraction in man (Abstract).
J. Physiol. (Lond.)
467:
75P,
1993.
19.
Greenhaff, P. L.,
Bodin K.,
Söderlund K.,
and
Hultman E.
Effect of oral creatine supplementation on skeletal muscle phosphocreatine resynthesis.
Am. J. Physiol. Endocrinol. Metab.
266:
E725-E730,
1994
20.
Gyulai, L. Z.,
Roth J. S.,
Leigh J. R.,
and
Chance B.
Bioenergetic studies of mitochondrial oxidative phosphorylation using 31phosphorus NMR.
J. Biol. Chem.
260:
3947-3954,
1985
21.
Harris, R.,
Söderlund K.,
and
Hultman E.
Elevation of creatine in resting and exercise muscles of normal subjects by creatine supplementation.
Clin. Sci. (Colch.)
83:
367-374,
1992[Medline].
22.
Hultman, E.,
Söderlund K.,
Timmons J. A.,
Cederblad G.,
and
Greenhaff P. L.
Muscle creatine loading in men.
J. Appl. Physiol.
81:
232-237,
1996
23.
Koszalka, T. R.,
and
Andrew C. L.
Effect of insulin on the uptake of creatine-L-14C by skeletal muscle in normal and x-irradiated rats.
Proc. Soc. Exp. Biol. Med.
139:
1265-1271,
1972[Medline].
24.
Kreis, R.,
Koster M.,
Kamber M.,
Felbinger J.,
Slotboom J.,
Walker G.,
Hoppeler H.,
and
Boesch C.
Effect of creatine supplementation upon muscle metabolism studied by 1H- and 31P-MRS, MRI, exercise performance testing and clinical chemistry.
In: Proceedings of the International Society of Magnetic Resonance in Medicine Annual Meeting New York April 2-May 3 1996. Berkeley, CA: International Society of Magnetic Resonance in Medicine, 1996, vol. 1, p. 25.
25.
Kushmerick, M.,
Meyer R. A.,
and
Brown T. R.
Regulation of oxygen consumption in fast- and slow-twitch muscle.
Am. J. Physiol. Cell Physiol.
263:
C598-C606,
1992
26.
Kuznetsov, A. V.,
Tiivel T.,
Sikk P.,
Kaambre T.,
Kay L.,
Danahsrad Z.,
Rossi A.,
Kadaja L.,
Peet N.,
and
Saks V. A.
Striking differences between the kinetics of regulation of respiration by ADP in slow-twitch and fast-twitch muscles in vivo.
Eur. J. Biochem.
241:
909-915,
1996[Web of Science][Medline].
27.
Loike, J. D.,
Zalutsky D. L.,
Kaback E.,
Miranda A. F.,
and
Silverstein S. C.
Extracellular creatine regulates creatine transport in rat and human muscle cells.
Proc. Natl. Acad. Sci. USA
85:
807-811,
1988
28.
McCann, D. J.,
Molé P. A.,
and
Caton J. R.
Phosphocreatine kinetics in humans during exercise and recovery.
Med. Sci. Sports Exerc.
27:
378-387,
1994.
29.
Meyer, R. A.
A linear model of muscle respiration explains monoexponential phosphocreatine changes.
Am. J. Physiol. Cell Physiol.
254:
C548-C553,
1988
30.
Meyer, R. A.
Linear dependence of muscle phosphocreatine kinetics on total creatine content.
Am. J. Physiol. Cell Physiol.
257:
C1149-C1157,
1989
31.
Meyer, R. A.,
Brown T. R.,
and
Kushmerick M. J.
Phosphorus nuclear magnetic resonance of fast- and slow-twitch muscle.
Am. J. Physiol. Cell Physiol.
248:
C279-C287,
1985
32.
Meyer, R. A.,
and
Foley J. M.
Testing models of respiratory control in skeletal muscle.
Med. Sci. Sports Exerc.
26:
52-57,
1994[Web of Science][Medline].
33.
Odland, L. M.,
MacDougall J. D.,
Tarnopolsky M.,
Elorriaga A.,
and
Borgamann A.
The effect of oral Cr supplementation on muscle [PCr] and short-term maximum power output.
Med. Sci. Sports Exer.
29:
216-219,
1997[Web of Science][Medline].
34.
Ponticos, M.,
Lu Q. L.,
Morgan J. E.,
Hardie D. G.,
Partridge T. A.,
and
Carling D.
Dual regulation of the AMP-activated protein kinase provides a novel mechanism for the control of creatine kinase in skeletal muscle.
EMBO J.
17:
1688-1699,
1998[Web of Science][Medline].
35.
Rose, W. C.,
and
Dimmitt F. W.
Experimental studies on creatine and creatinine. VII. The fate of creatine and creatinine when administered to man.
J. Biol. Chem.
XXVI:
345-353,
1916.
36.
Sahlin, K.,
Harris R.,
and
Hultman E.
Creatine kinase equilibrium and lactate content compared with muscle pH in tissue samples obtained after isometric exercise.
Biochem. J.
152:
173-180,
1975[Web of Science][Medline].
37.
Saks, V. A.,
Belikova Y. O.,
Kuznetsov A. V.,
Khuchua Z. A.,
Branishte T. H.,
Semenovsky M. L.,
and
Naumov V. G.
Phosphocreatine pathway for energy transport: ADP diffusion and cardiomyopathy.
Am. J. Physiol.
Suppl. (Oct.) 261:
30-38,
1991.
38.
Saks, V. A.,
Rosenshtraukh L. V.,
Smirnov V. N.,
and
Chazov E. I.
Role of creatine phosphokinase in cellular function and metabolism.
Can. J. Physiol. Pharmacol.
56:
691-705,
1978[Web of Science][Medline]
39.
Savabi, F.
Free creatine available to the creatine phosphate energy shuttle in isolated rat atria.
Proc. Natl. Acad. Sci. USA
85:
7476-7480,
1988
40.
Schneider, C.,
Stull G. A.,
and
Apple F. S.
Kinetic characterization of human heart and skeletal muscle CK isoenzymes.
Enzyme
39:
220-226,
1988[Web of Science][Medline].
41.
Seraydarian, M. W.,
Artaza L.,
and
Abbott B. C.
Creatine and the control of energy metabolism in cardiac and skeletal muscle cells in culture.
J. Mol. Cell Cardiol.
6:
405-413,
1974[Web of Science][Medline].
42.
Sipilä, I.,
Rapola J.,
Simell O.,
and
Vamas A.
Supplementary creatine as a treatment for gyrate atrophy of the choroid and retina.
N. Engl. J. Med.
304:
867-870,
1981[Abstract].
43.
Snow, R. J.,
McKenna M. J.,
Selig S. E.,
Kemp J.,
Stathis C. G.,
and
Zhao S.
Effect of creatine supplementation on sprint exercise performance and muscle metabolism.
J. Appl. Physiol.
84:
1667-1673,
1998
44.
Tonkonogi, M.,
Harris B.,
and
Sahlin K.
Mitochondrial oxidative function in human saponin-skinned fibers: effects of prolonged exercise.
J. Physiol. (Lond.)
510:
270-286,
1998.
45.
Vanderberghe, K.,
Goris M.,
Van Hecke P.,
Van Leemputte M.,
Vangerven L.,
and
Hespel P.
Long-term creatine intake is beneficial to muscle performance during resistance training.
J. Appl. Physiol.
83:
2055-2063,
1997
46.
Veksler, V. K.,
Kuznetsov A. V.,
Anflous K.,
Mateo P.,
van Deursen J.,
Wieringa B.,
and
Ventura-Clapier R.
Muscle creatine kinase-deficient mice. II. Cardiac and skeletal muscles exhibit tissue-specific adaptation of the mitochondrial function.
J. Biol. Chem.
270:
19921-19929,
1995
47.
Vøllestad, N. K.,
and
Blom P. C.
Effect of varying exercise intensity on glycogen depletion in human muscle fibres.
Acta Physiol. Scand.
125:
395-405,
1985[Web of Science][Medline].
48.
Yamashita, K.,
and
Yoshioka T.
Profiles of creatine kinase isoenzyme compositions in single muscle fibres of different types.
J. Muscle Res. Cell Motil.
12:
37-44,
1991[Web of Science][Medline].
This article has been cited by other articles:
|
|
 |
|
  A. M. Jones, D. P. Wilkerson, and J. Fulford Influence of dietary creatine supplementation on muscle phosphocreatine kinetics during knee-extensor exercise in humans Am J Physiol Regulatory Integrative Comp Physiol, April 1, 2009; 296(4): R1078 - R1087. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. M. Damon and J. C. Gore Physiological basis of muscle functional MRI: predictions using a computer model J Appl Physiol, January 1, 2005; 98(1): 264 - 273. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. A. Smith, S. J. Montain, G. P. Zientara, and R. A. Fielding Use of phosphocreatine kinetics to determine the influence of creatine on muscle mitochondrial respiration: an in vivo 31P-MRS study of oral creatine ingestion J Appl Physiol, June 1, 2004; 96(6): 2288 - 2292. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. E. Huso, J. S Hampl, C. S. Johnston, and P. D. Swan Creatine supplementation influences substrate utilization at rest J Appl Physiol, December 1, 2002; 93(6): 2018 - 2022. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. Jones, H. Carter, J. S. M. Pringle, and I. T. Campbell Effect of creatine supplementation on oxygen uptake kinetics during submaximal cycle exercise J Appl Physiol, June 1, 2002; 92(6): 2571 - 2577. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B Walsh, M Tonkonogi, K Soderlund, E Hultman, V Saks, and K Sahlin The role of phosphorylcreatine and creatine in the regulation of mitochondrial respiration in human skeletal muscle J. Physiol., December 15, 2001; 537(3): 971 - 978. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
